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					NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


Objective

1.   From a list, identify geotechnical tests as index or engineering property
2.   Explain the difference between index properties and engineering properties
3.   Explain the difference between quantitative and qualitative analyses
4.   List the engineering analyses associated with each engineering property test

Introduction

Two broad categories of soil properties are often discussed by soils engineers. One
category is termed Index Properties, and the other, Engineering Properties.

 Index Properties are measurements of soils' gradation, Atterberg limits, specific
gravity, dry unit weight, water content, dispersion properties, and others. These
properties give indications of a soils' probable behavior, but give no numerical values
useable in an engineering analyses such as a slope stability analysis. Index properties
permit only qualitative estimates. Engineering behavior may be quantitatively predicted
from index properties and USCS classifications. The Unified Soil Classification System
uses index properties to group soils on the basis of the probable engineering behavior.
Field classification of soils without actually measureing index properties such as
gradation, Atterberg limit, or dry unit weight and water content will be less accurate than
estimates based on actual index property tests.

Engineering Properties consist of measured physical constants that are useable in
engineering calculations. A soil's coefficient of permeability, its unconfined compressive
strength value, and the compression index from a consolidation test are examples of
engineering properties.

The engineering property categories are as follows:

PERMEABILITY                          COMPRESSIBILITY
SHEAR STRENGTH                        SHRINK-SWELL POTENTIAL

Each of the engineering property tests are quantitative measurements of a soil’s behavior
that may be entered into a quantitative analyses summarized as follows:

Shear Strength – Slope Stability, including Finite Element Analyses

        Values of the strength of a soil sample are measured under the appropriate
        laboratory conditions that simulate field conditions. The test parameters are used
        in analyses to predict a safety factor for the design being evaluated.




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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


Consolidation – Settlement Analysis, including Finite Element Analyses

Values of the compressibility characteristics of a soil sample are measured under the
appropriate laboratory conditions that simulate field conditions. The test parameters are
used in analyses to predict the settlement caused by the loads imposed by a structure
being evaluated.

Permeability – Seepage Analysis, including Finite Element Analyses

       Values of the permeability characteristics of a soil sample are measured under the
       appropriate laboratory conditions that simulate field conditions. The test
       parameters are used in analyses to predict the seepage quantities, head losses, and
       hydraulic gradients caused by water flowing through or under a structure being
       evaluated.

Shrink/Swell – Swell or Heave Analysis, including Finite Element Analyses

       Values of the shrink/swell characteristics of a soil sample are measured under the
       appropriate laboratory conditions that simulate field conditions. The test
       parameters are used in analyses to predict the swell pressures, predicted vertical
       heave, or shrinkage caused by thermal stresses imposed on a soil/structure system.

Limitations of Predicting Engineering Behavior from Index Tests

Estimating soils' engineering behavior only from its USCS classification and other
limited data has limitations. The 15 major USCS classes include a variety of soils.
Significant factors affecting the engineering properties of the soils are not included in this
classification system. Important variables such as density, degree of saturation, stress
history, and others with which you will become familiar are very important to the
engineering properties of soils. Substantial variation in engineering properties may occur
within USCS classes.

The pitfalls to relying only on classification for engineering interpretations are expressed
well by Lambe and Whitman in their 1969 text, Soil Mechanics. The following quotation
is important to remember:

       Soil classification has proved to be a valuable tool to the soil engineer. It helps
       the engineer by giving him general guidance through making available in an
       empirical manner the results of field experience.

       The soil engineer must be cautious, however, in his use of soil classification.
       Solving flow, compression, and stability problems merely on the basis of soil
       classification can lead to disastrous results.

       ...empirical correlations between index properties and fundamental soil behavior
       have many large deviations.



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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests

Qualitative evaluation of soils' engineering properties is important in much NRCS
engineering work. Frequently, projects do not justify extensive site investigation and
laboratory testing. Field classifications based on augered holes are useful if done
properly. Estimates of soils' engineering behavior on the basis of USCS classification
and limited data is best used when:

       1. Grouping soils to select representative horizons and depths for sampling or
           further testing.

               For instance, a sand horizon may be defined from several borings beneath
               a planned waste storage pond. Based on field classification, the horizon is
               determined to be very uniform. A representative sample may be obtained
               for gradation analysis to estimate its permeability. Based on borings and
               field classification, a nearby borrow area is determined to have two soil
               types. Field classifications may be used to select samples for testing to
               determine which soil type is best for a soil blanket.

       (2) Qualitatively evaluating several potential sites for a project or structure to
       determine which has fewer problems and is more suitable.

               For instance, borings at one site indicate that soils at grade are very silty
               sands, SM, while at a nearby location, soils at grade are CL. Qualitative
               behavior characteristics will influence which site is most suitable,
               depending on what type of structure is being planned. One site may be
               most suitable if a pond is being located, while the other may be preferable
               if a concrete structure is being planned.

       (3) Preliminary design of a site, evaluating alternatives for design of the site.
       Field classifications of horizons at a planned pond site may determine what depth
       of cutoff is required, what horizons are better for the clay core of the
       embankment, and other important design decisions may be based on borings in
       the foundation and borrow area of the structure.

Examples of Estimates Based on Index Properties:

Estimating Standard Proctor Test Results:

                       d max = 130.3 –0.82* LL + 0.3* PI

                       wopt (%) = 6.77 + 0.43* LL – 0.21* PI

Qualitatively Evaluating Shrink Swell Potential ( see chart on following page)




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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


                             Prediction of Shrink-Swell Class


      80
      70
      60
      50                                         Very High
 PI




      40
      30
                                          High
      20                   Medium

      10                                                 Low

       0
           0        10        20        30        40         50       60          70   80
                                       Percent 2 microns
                   PI                               Shrink/Swell Potential
                  < 20                                      Low
                 12-34                                    `Medium
                 23-45                                      High
                  > 32                                   Very High

Empirical Estimate of Swell Pressure

                    1.858  0.0208  LL  0.01065   dry  0.0269 * w (%)
 P( tsf )  10
Estimating Compression Index from Consolidation Test




                   Cc  0.0035  LL  e0  0.4 

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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests




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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


LIMITATIONS OF ESTIMATES BASED ONLY ON CLASSIFICATION

PROBLEM:

For each of the following situations, recommend whether a design should be based on
index property tests or whether samples should be submitted for engineering property
tests.
Field classification of all samples during the site investigation using the Unified Soil
Classification System is assumed. Recommend one of three options for each situation
discussed,

A. Rely only on field logging of drill holes or backhoe pits, with no samples submitted to
      the laboratory.

B. In addition to A. obtain a few small samples and submit them to a soil laboratory for
       gradation analyses, Atterberg limit, dispersion, and natural water content tests.

C. In addition to A and B, obtain large samples for compaction tests and undisturbed
       samples. Request a soils lab to perform engineering property tests in addition to
       the tests requested in A and B.

1. A small grade control structure is planned. The maximum height of water stored in
the structure will be about 15 feet. Soils in the area are known to be fine-grained. No
problems have been detected with dispersion


2. An irrigation reservoir is planned for a site. The site will store about 20 feet of
permanent water. The hazard classification is "b" due to a county road downstream. The
embankment will contain about 20,000 cubic yards of fill.


3. A waste storage lagoon is planned. It will be about 1.5 acres in size. The planned
depth of water is 8 feet. The site is in a recharge area for an aquifer used locally for rural
water wells.

4. A large concrete tank is to be installed. The proposed site is in a flood plain where
soft clay soils are known to exist. The concrete tank has an estimated construction cost
of $ 45,000.

5. A stream bank restoration project is being planned. Slopes show signs of instability.
   The length of the project is two miles, and the depth of the channel is 10 feet.

Refer to the following page for a discussion of each situation.




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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


PROBLEM DISCUSSION:

(1) Level A recommended. Designing on the basis of soil classification without
sampling and testing is satisfactory. Complex tests would not be required. Field testing
for dispersive clays, covered later in other modules could be a recommendation.

(2) Level C recommended. Designing this size and hazard class structure solely on the
basis of field classification with no samples would be inadvisable.

(3) Level C is recommended. State regulations may control investigative requirements
for many such structures. If particularly unfavorable soils are indicated by the
preliminary investigation, samples and laboratory tests may be required, particularly if
any type of clay blanket is required for the design.

(4) Level C recommended. Due to the cost of the structure and the possibility of
unfavorable bearing strength in the alluvial clays, a detailed investigation with sampling
and laboratory testing is recommended.

(5) Level B is recommended. Characterizing the soils present together with observations
on the stream mechanics and geomorphology and groundwater observations should
provide adequate basis for designing the planned works.


PROBLEM:

For each of the following described properties/test values listed below, categorize the
described item as one of the following,

INDEX PROPERTY or ENGINEERING PROPERTY

1. An intact clod of soil is obtained and the dry unit weight and water content of the
     sample are obtained. From an assumed value of specific gravity, the percent
     saturation is determined. Percent saturation is a(n)
     ___________________________________________.

2.    During augering a horizon, the consistency of the soil and the relative water content
     are noted and described. Such descriptions are examples of:
     ________________________________________________

3.    Measurements are performed of the amount of water which flows out of a cased drill
     hole in a site investigation. A coefficient of permeability is calculated from the
     measurements. The coefficient of permeability is an example of:
     ________________________________________________

4. To perform a slope stability analysis, one must have estimates or test data measuring
     the ________________________________________ of a soil. .



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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


PROBLEM SOLUTION:

1. An intact clod of soil is obtained and the dry unit weight and water content of the
   sample are obtained. From an assumed value of specific gravity, the percent
   saturation is determined. Percent saturation is an index property. While this value
   may be used for other calculations, it is not used directly in analyses such as slope
   stability, settlement, or seepage quantity estimates. It is not an engineering property
   as defined.
2. Descriptions of consistency and relative density are examples of index data for
   samples. Indirectly, one is evaluating the density of the soil and its plasticity, both
   index properties. Engineering property parameters such as  angle, coefficient of
   permeability, etc., are not obtained.

   (3) A coefficient of permeability is an engineering property of a soil.

   (4) To perform a slope stability analysis, one must have estimates or test data
   measuring the engineering properties (shear strength) of a soil. To evaluate
   whether one soil may be preferable over another, one only needs to evaluate the
   qualitative engineering behavior of the soils.




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NPEG – Geotechnical Engineering, Module 1, Index and Engineering Property Tests


Systems of Measurement and Conversion Factors
             Length                  1 in.            = 25.40 mm
                                                      = 2.540 cm
                                                      = 2.540 x 10-2 m
                                     1 ft             = 30.48 cm
                                                      = 3.048 x 10-1 m
                                                     -3
                                     1 micron= 1 x 10 mm
                                     1m               = 39.37 in.
                                                      = 3.28 ft

             Area                    1 sq in .        = 6.452 cm2
                                     1 sq ft          = 9.29 x 102 cm2
                                                      = 9.29 x 10-2 m2
                                     1 cm2            = 1.55 x 10-1 sq in.
                                     1 m2             = 10.76 sq ft

             Volume 1 cu in .        = 16.387 cm3
                                     1 cu ft          = 2.832 x 10-2 m3
                                     1 cm3            = 1 ml
                                                      = 6.10 x 10-2 cu in.
                                     1 m3             = 35.31 cu ft

             Mass                    1 lb             = 453.6 g
                                                      = 4.536 x 10-1 kg
                                     1 kip            = 1 x 103 lb
                                                      = 4.536 x 102 kg
                                     1 kg             =2.2046 lb
                                                      = 2.2046 x 10-3 kips
             Time                    1 day            = 8.6400 x 104 s
                                     1s               = 1.157 x 10-5 day

             Pressure(mass)          1 psi            = 7.03 x 10-2 kg/cm2
                                     1 psf            = 4.88 x 10-4 kg/cm2-
                                     1 ksf            = 4.88 x 10-1 kg/cm2
                                     1 kg/cm2 =       2.048 x 103 psf

             Pressure(force)         1 psi            = 6.89 kPa
                                     1 kPa            = 0.1451 psi

             Unit weight (density)   1 pcf            = 1.602 x 10-2 g/cm3
                                     1 g/cm3          = 62.4 pcf

             Permeability            1 fps            = 30.48 cm/s
                                     1 fpd            = 3.53 x 10-4 cm/s
                                     1 cm/s           = 2.8346 x 103 fpd

             Angle                   1 deg            = 1.745 10-2 rad
                                     1 rad            = 57.3 deg




                                               9
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

Objectives - Geotechnical Analyses

1. List methods for performing slope stability analyses
2. List methods for performing settlement analyses
3. List methods for performing seepage analyses
4. List parameters needed for each type of Geotechnical Analyses
       Slope Stability
       Settlement
       Seepage
       Shrink/Swell
       Lateral Earth Pressure Computations

Slope Stability Methods Used
       Charts - Navdocks example
       Empirical guidelines
       Computerized Analyses
               UTEXAS3
               WINSTABL and PCSTABL6
               SLOPE/W
Others
Infinite Slope Equations for Saturated Sands and Silts
Chart for Estimating Safety Factor of Excavated Slope in Clay (Navdocks)
Example Problem Excavated Slope in Clay (Navdocks)
Given:
Slope Height = 22 feet
c parameter = 450 psf
Saturated Unit Weight = 123 pcf
Compute safety factor for 3:1 slope
If FS is less than 1.4, determine what slope is required to achieve a FS of 1.4
Solution Problem Excavated Slope in Clay (Navdocks)
First calculate parameter d = D  H
d = 11  22 = 0.5
From Chart, Read No = 7

Solution Problem Excavated Slope in Clay (Navdocks)
Usually, safety factor of 1.4 is desirable for excavated slope
Determine what slope would be stable
Rearrange equation to solve for No
Solution Problem Excavated Slope in Clay (Navdocks)
From chart with d = 0.5, read across from No value of 8.4 and read slope cotangent is
about 4:1


                                             1
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

NPEG Stability Chart

Empirical Guidelines

      Experience is that well compacted earth fills on competent foundations are stable
      on 3:1 slopes up to heights of about 30 feet.

      Exception to empirical guidelines are highly plastic clay embankments - may
      require slopes from 4:1 to 6:1

      Saturated zones of fine slightly silty sand require flatter slopes  4:1

Computerized Analyses

      Least expensive is WINSTABL
      Most expensive is SLOPE/W
      Steep Learning Curve
      Experience needed to assess input parameters
      Most important use is to compare effect of alternatives on safety factor




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NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses


            Introduction to Slope Stability Analyses for Cohesionless Soils

Slope stability in purely cohesionless, sands and silts is studied with 3 equations referred
to as infinite slope equations. These equations relate the steepness of the slope, the unit
weight of the soils in the slope, the friction angle of the soils, and seepage forces at the
slope face, to calculate a safety factor. Because the assumption for this analysis is that
the soils have zero cohesion, the height of the slope is not a factor. The same safety
factor is calculated for any height of slope. A safety factor of 1.1 is commonly regarded
as acceptable for this condition, because the failures are shallow sloughing types of
failures and not usually disastrous in nature. The general acceptance of a lower safety
factor for this type of analysis is detailed in the last section of this Appendix. Infinite
slope equations are explained, with their applications in more detail as follows:

Infinite Slope Equations

       Moist Slope Equation

       If no seepage is exiting the slope face being examined, the safety factor for that
       slope is simply stated as:

                                          FS  mtan'
       where,
                m       =      slope cotangent
                ’      =      internal friction angle of cohesionless slope soil

       Consider the example for 3:1 side slopes and soils with an effective ’ angle of 26
       degrees, the calculated safety factor is:

                                          FS  3 tan 26

                                             FS  1.46


       Seepage Parallel to Slope

       When seepage exits the slope face and the direction of the flow is parallel to the
       slope face, this equation is applicable. This pattern of seepage would be predicted
       in very homogeneous soils with little or no horizontal layering. This assumption
       is typically not used to represent soil that has been compacted in layers or in
       alluvial soils. The equation is:

                                                 b  tan' 
                                         FS 
                                                 sat  tan
       or, rewritten,



                                              3
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

                                                   b
                                       FS  m           tan' 
                                                   sat
       where,
                       m       =       Slope Cotangent (slope angle,)
                       b      =       Buoyant Unit Weight
                       sat    =       Saturated Unit Weight
                       ’      =       Effective Friction Angle

HORIZONTAL SEEPAGE

       This equation assumes that the seepage forces acting on the soils in the slope are
       due to flow along horizontal planes.


                                FS 
                                      sat  cos2    w  tan' 
                                             sat  sin cos
       or, rewritten

                                   FS 
                                         b  m 2   w  tan' 
                                                   m  sat

Analyses where the Effective Cohesion is Significant

In silty, clayey coarse-grained soils, or for soft clay deposits, a significant cohesion
property may be present in effective stress parameters. For this assumption,
computerized slope stability analyses can be used to calculate safety factors by the
method of slices. This type of computer analyses is not appropriate for zero cohesion
soils, because the critical failure arcs will be very shallow on the slope face, with safety
factors approaching those obtained using the infinite slope equations.

Documentation of Adequacy of Lower Safety Factors for Infinite Slope Analyses

In evaluating the adequacy of a design, geotechnical engineers have target safety factors
by which a design is judged adequate. In an infinite slope analyses involving
cohesionless soils, safety factors of from 1.0 to 1.1 are commonly used as criteria by the
engineering profession. This is documented with the following four references. This
criterion is contrasted to the normally required safety factor of 1.5 used to judge the long-
term downstream steady seepage case for soils with cohesion. Although this different
criterion for infinite slope stability is well accepted, some administrative codes have not
included this important facet of slope stability analyses. The absence of this detail from
codes does not change the accepted geotechnical practice, however.




                                              4
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

1. Soil Conservation Service, TR-60, “Earth Dams and Reservoirs,” October, 1985, page
5-5, footnote to Table 5-2,
                Use infinite slope stability analysis whenever the c or c’ intercept strength
                is zero for soils that are tested to simulate low confining pressures. This
                situation exists for failure surfaces located near the embankment surface.
                Minimum factor of safety for the Infinite slope stability analysis is 1.1
2. Lambe, T. William and Robert V. Whitman, Soil Mechanics, John Wiley and Sons,
New York. 1969. Page 193.
                The only unknown factor in the stability of an infinite slope is the
                appropriate value for the angle of internal friction. This quantity can be
                estimated with reasonable accuracy and, furthermore, the consequences of
                failure of such a slope are slight. Hence the safety factor does not need to
                be large. Usually an engineer will be conservative in his choice of  = cv,
                and will use FS = 1.
3. Sherard, James L, et al, Earth and Earth-Rock Dams, John Wiley and Sons, New
York, 1963. p. 155,
                Almost all slides during construction and all deep upstream and
                downstream slides after construction have occurred in dams underlain by
                foundations of clay relatively high in plasticity and natural water content.
                .. From these statistics and from experiences common to many engineers,
                there seems to be justification for the statement that rolled-earth dam
                embankments have not failed by sliding unless the embankments or the
                foundations consisted of relatively fine-grained soils.

4. Casagrande, Arthur, “Notes on the Design of Earth Dams, Journal of the Boston
Society of Civil Engineers, October, 1950, Volume xxxvii, Number 4.

While I am discussing questions pertaining to stability analysis, I should like to stress an
important difference in the meaning of factor of safety as applied to sand and gravel or to
clay. A slope consisting of sand which is in such a condition that it cannot liquefy (that
is, either compact enough, or else not subject to saturation) and which rests on a stable
foundation, will stand safely with such steep slopes that the factor of safety is unity. In
such a case a factor of safety = 1.0 indicates that any additional material which is dumped
on the slopes will merely roll down the slope without producing a failure condition within
the dam. In contrast, when we deal with clay, a factor of safety of unity means that a
major failure of the dam is imminent. When carrying out stability analyses, it is
important to keep this difference in mind, and to remember that it is illogical to apply the
same criteria to the numerical value of the factor of safety for compacted sand and
gravels




                                              5
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

Corps of Engineers Equation for slightly cohesive sands

                                                          
                                  z   b  cos   tan ' 
                                                                    c'
                                                                  cos 
                           FS 
                                           z   sat  sin  




         z                Soil with strengthunit weight
                          band sat




                      

Infinite Slope Analyses

       Applicable to relatively clean sands and gravels
       Predict safety against shallow sloughing of slope
       Different equations used depending on seepage forces




                                            6
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

Consolidation

      Methods Used
      Finite Element
      Empirical guidelines
      Computerized Analyses including spreadsheets
      Terzaghi equations
      Taylor’s equations
      Joint gap estimates for conduits (TR-18)

Finite Element Analyses

      Corps of Engineer Publication Engineering Technical Letter 1110-2-544 has good
      basic explanations - Appendix A, Geotechnical Analysis by the Finite Element
      Method
      Examples of evaluations
      Potential for cracking of dams
      Potential for hydraulic fracture in dams
      Settlement and horizontal movements
      Conventional Settlement Analyses
      Conventional Settlement Analyses
      Conventional basic explanations - Appendix A, Geotechnical Analysis by the
      Finite Element Method
      Examples of evaluations
      Potential for cracking of dams
      Potential for hydraulic fracture in dams
      Settlement and horizontal movements

Lateral Earth Pressure

      Methods Used – NRCS publication TR 74, Lateral Earth Pressure
      Corps of Engineers EM 1110-2-2502
      NAVDOCKS Design Manual 2, Chapter 3
      CE Sheet Pile Program CWALSH
      Empirical guidelines
      Active and Passive Earth Pressure Coefficients
             Active – Wall moves away from the soil
             Passive – Soil is compressed horizontally – only applies to cohesionless
             soils
             Based on Friction Angle of Backfill
             Determined from estimated relative density and soil classification


Seepage

      Methods Used
      Finite Element
      Empirical guidelines


                                          7
 NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

       Manual Flow nets - See Soil Mechanics Note 5
       Uplift Calculations - See Soil Mechanics Note 7
       Finite Element Analyses
       Corps of Engineer Publication Engineering Technical Letter 1110-2-544 has good
       information on Finite Element Analyses

 Empirical Guidelines

       Lane’s Creep Ratio
       Soil Type                    Creep Ratio
       Very fine sand or silt          8.5
       Fine Sand                       7.0
       Medium Sand                     6.0
       Coarse Sand                     5.0
       Fine Gravel                     4.0
       Medium Gravel                   3.5
       Coarse gravel
          including cobbles            3.0
       Boulders with some cobbles
          and gravel                   2.5
       From E.W. Lane
       Lane, E.W., Security from under-seepage masonry dams on earth foundations,
       Transactions, ASCE, 100, pp. 1235-1351.




              HW
                                                                         TW




                                                           Lw
    K                                             Cw 
Lw  v  Lh  Lv                                         HW  TW
    Kh



                                          8
NPEG – Geotechnical Engineering, Module 2, Geotechnical Analyses

Uplift Analyses – Soil Mechanics Note 7 discusses calculations of embankments or
levees where a less permeable clay horizon overlies a more pervious sand horizon. The
uplift pressures in the sand horizon can create sand boils, and relief wells are sometimes
used to solve the problem. Soil Mechanics Note 7 covers the mathematics of analyzing
the problem and Soil Mechanics Note 3 covers design of relief wells. The Corps of




Engineers also has an excellent design manual for relief wells, EM 1110-2-19.




                                             9
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays


OBJECTIVES

1. List important parameters used to characterize clay soils

2. Use index data to estimate the consistency of clay soils

3. Use correlations to estimate the undrained shear strength of clay soils

INTRODUCTION. Consistency descriptions for fine-grained soils should be limited to
those soils with appreciable plasticity, usually with a PI of 10 or higher. Nonplastic silts
behave more similarly to sands and should be examined and described in terms of relative
density rather than consistency. For purposes of this discussion, a term used to describe
these fine-grained soils is cohesive. Cohesive means that soils have plasticity indices
greater than 10, with a relatively low percentage of sand or gravel. The Unified Soil
Classification System groups to which these concepts apply are primarily CL, CH, and a
few MH soils.

IDENTIFY ORIGIN

Weathered Bedrock (Shale, Limestone, etc.)
Residual
Colluvial
Alluvial
Lacustrine
Glaciated Till
Windblown

IDENTIFY INDEX PROPERTIES

1. Percent clay (% finer than 2m)

Determined from hydrometer analysis on part of sample smaller than # 10 sieve
In evaluating percent clay for Atterberg limit comparisons, regrade on the # 40 sieve

2. Percent 2 microns

Atterberg limit tests are performed on the portion of a sample that is finer than a #40
sieve. With gravelly samples, you must mathematically eliminate the oversize particles to
determine the clay size
Example - The percent finer than the #40 sieve is 67 percent and the percent clay is 37
percent. What is the corrected % finer than 2 m ?

To correct, divide by the percent finer than the # 40 sieve. This will obtain the percent of
the minus # 40 sieve that is finer than 2 microns

Correlation between clay content and Atterberg limits is shown on Next Page




                                             1
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays


                    Estimating LL and PI from Percent and Type of Clay
                    (Note use percent of minus #40 sieve for Evaluation)

                Montomorillonitic            Mixed Class w/               Mixed Class w/
 Percent             Class                Considerable 2:1 clays       Considerable 1:1 clays
2 microns       LL           PI             LL            PI             LL            PI
   10           26            9             21             4             16             3
   12           28           11             23             6             18             4
   14           30           12             25             7             20             5
   16           32           14             26             8             21             6
   18           34           15             28             9             23             7
   20           36           17             30            11             25             8
   22           38           19             32            13             27             9
   24           40           20             34            14             29            10
   26           42           22             35            15             30            11
   28           44           23             37            16             32            12
   30           46           25             39            18             34            13
   32           48           27             41            20             36            14
   34           50           28             43            21             38            15
   36           52           30             44            22             39            16
   38           54           31             46            23             41            17
   40           56           33             48            25             43            18
   42           58           35             50            27             45            19
   44           60           36             52            28             47            20
   46           62           38             53            29             78            21
   48           64           39             55            30             50            22
   50           66           41             57            32             52            23
   52           68           43             59            34             54            24
   54           70           44             61            35             56            25
   56           72           46             62            36             57            26
   58           74           47             64            37             59            27
   60           76           49             66            39             61            28

  These correlations were developed in the 1960's by NRCS soil scientists from regression
                                         analyses.

The scientists suggest not using the correlations for kaolinitic type clays.




                                         2
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays

Characterizing Clays

2 - Liquid Limit
Water content at which groove closes for 1/2”under 25 blows of cup

3 - Plastic Limit

Water content at which 1/8” thread can be rolled and just begins to crack

4 - Plasticity Index - The numerical difference between the Liquid Limit water content
and the Plastic Limit water content

                                            PI = LL - PL
BACKGROUND. Clays can exist at a variety of density conditions. The density of a
clay soil is directly related to its stress history. When clay soils are first deposited in a
low energy environment, they have a water content above their liquid limit water content
value, usually. If the clays are subjected to consolidation pressures due to addition of
overburden or desiccation, they become more dense and have a lower saturated water
content. Clays may become consolidated from the weight of additional material
deposited on top of them. Over time, the added weight of the overburden consolidates
the clays. Another way that clays can become consolidated is from glaciation. The
weight of an ice sheet several hundred feet thick is considerable. One of the most
common ways that clays become consolidated is from desiccation. While the process of
desiccation is not strictly speaking a consolidation, the effect is the same, the clay
becomes more dense as water is withdrawn by the thermal energy of the sun. At water
contents above the liquid limit, clays have very soft consistency. At water contents less
than the soil's plastic limit, clays are very stiff in consistency. The saturated consistency
of a clay deposit gives clues to its stress history. Normally consolidated clays are usually
soft to very soft. Preconsolidated clays are stiff to very stiff in saturated consistency.

FIELD CONSISTENCY EVALUATION – Clays should only be evaluated for
consistency in a saturated condition to have the same frame of reference. Consistency
will vary with water content, and a saturated condition furnishes the only datum from
which all soils can be compared. You should rely on other methods, covered below, for
attempting to qualitatively evaluate the consistency of clays above the water table.
However, if you are examining a soil deposit in a saturated state, the following rules of
thumb are useful in qualitatively describing the consistency of the soil. The saturated
consistency has a strong influence on the probable engineering characteristics of a clay
soil.

Very soft clays are very low in shear strength, high in compressibility, have poor
workability, a high shrinkage potential, and a lower resistance to erosion than more firm
clays. Very stiff clays have high shear strength, with exceptions, low compressibility,
and low shrinkage potential. They have a high potential for swell. Very stiff clays are
often weakened by a network of fine cracks and a blocky structure. This causes them to
have low shear strength in excavated slopes. They are much more permeable than their
Unified Classification would indicate.


                                              3
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays



SATURATED
CONSISTENCY                     DESCRIPTION

Very Soft               Thumb will penetrate soil more than 1 inch
                        Extrudes from between fingers when squeezed in fist

Soft                    Thumb will penetrate soil about 1 inch. Easily molded in fingers.

Firm                    Thumb will not penetrate soil, but will indent soil about 1/4 inch.
                        Molded by strong finger pressure is Firm. Cannot be molded by
                        finger pressure, but can be indented by thumb is Stiff.

Hard                    Thumb will not indent soil but thumbnail will.
                        Also referred to as Very Stiff.

Very Hard               Thumbnail will not indent soil

Note: Some engineers use the terms Stiff and Very Stiff to modify the term Firm in the
above table.

 CONSISTENCY DIAGRAM - Another method of evaluating saturated consistency of
clay soils is to relate the saturated water content of the soil to its liquid limit and plastic
limit water contents. Very soft soils exist at saturated water contents greater than their
liquid limits. Hard to very hard soils (stiff to very stiff) exist at saturated water contents
below the plastic limit water content.

This method is essential when examining soils above the water table, since the saturated
consistency cannot be visually/manually evaluated. To use this method, you must have
measured or estimated values of the soil's dry unit weight, liquid limit, and plasticity
index. Field tests are available for measuring dry unit weight, but the liquid limit and
plasticity index tests are usually performed by a soil laboratory. The method is
summarized as follows:

        Step 1 - Measure, or estimate the dry unit weight of the soil horizon. If you know
                the moist unit weight and the water content, the dry unit weight is
                calculated as[ m/(1+(w%/100)], where m is the moist unit weight,
                expressed in either pounds per cubic foot or grams per cubic centimeter
                and w% is the water content in percent.
        Step 2 - Calculate the theoretical saturated water content of the soil from the
        following equation. For a value for Gs, specific gravity, assume a value of 2.70.
        This assumption is not critical.
                                                       1 
                                   w sat (%)   water       100
                                                 dry
                                                        Gs 
                                                            

        Step 3 - Construct a scaled sketch of water content, showing the liquid limit,
                plastic limit, and saturated water content as shown on the following page


                                               4
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays




                                                             5
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays

EXAMPLE 1:

       GIVEN: A soil has a moist unit weight of 122.5 pounds per cubic feet and a water content
       of 18.2 percent. The soil has a liquid limit of 38 and a PI of 16. Assume the soil has a
       specific gravity of 2.70.


       FIND: The saturated consistency of the sample.

       SOLUTION:

       Step 1. Calculate the dry unit weight of the sample. Use the equation
       d = [ m/(1+(w%/100)] = [122.5/(1.182)] = 103.6 pcf

       Step 2. Calculate the theoretical saturated water content,


                           1 
       w sat (%)   water       100
                     dry
                               
                             Gs 



       wsat (%)  
                    62.4    1 
                  103.6  2.68   100
                               

              =       23.2 %

       Step 3. Construct a consistency diagram        wsat = 23.2 % - therefore the saturated
       consistency is stiff.

PROBLEM:

GIVEN: You are evaluating the foundation at two sites. You determine that the soil at both sites
has a dry unit weight of 1.45 grams/cm3. However, the soil at site 1 has a LL = 70 and PI = 40, and
the soil at site 2 has a LL = 42 and PI = 24.

FIND: The saturated consistency of both soils and state generally which soil has the poorer
engineering properties.




                                                  6
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays

PROBLEM SOLUTION:

Step 1. Calculate the theoretical saturated water content (the same for both samples):

                                                         1 
                                    w sat (%)   water       100
                                                 d      Gs 


                                                      1 
                                   wsat (%)   water      31 .9%
                                               1.45 2.7 

Step 2 Construct a consistency diagram for the soil at site 1:

PL = LL-PI = 70-40 = 30 %

 wsat = 31.9 % - therefore the saturated consistency is stiff.

       Step 3. Construct a consistency diagram for the soil at site 2:

       PL = LL-PI = 42-24 = 18 %


        wsat = 31.9 % - therefore the saturated consistency is medium.

       The soil at site 1 has a more stiff consistency than the soil at site 2. It should have higher
       shear strength and lower compressibility. Due to its higher plasticity, it will have more swell
       potential when wetted. Since the soil at site 1 is a stiff clay of high plasticity, it may have a
       blocky structure and be unstable in excavated slopes.


Liquidity Index

Another method for characterizing the saturated consistency of clays rather than using a consistency
diagram is to calculate a term called liquidity index. Liquidity Index is defined as follows:


                        w sat  PL   w sat  LL  PI
            LI                    
                             PI             PI




                                                    7
NPEG – Geotechnical Engineering, Module 3, Characterizing Clays


     Liquidity                 Saturated
     Index                     Consistency
       <0                      Very Stiff
     0 to 0.33                 Stiff
     0.33 to 0.67              Medium
     0.67 to 1.00              Soft
       > 1.00                  Very Soft

Example of Problem Type Clay

Soft Clays.

 The average Liquid Limit value of Mexico City Clay is 260%. The average water content of the
soils is 256% . Groundwater withdrawal has caused subsidence

Stiff Fissured Clays.

Clays that have a saturated water content that is near their plastic limit water content % are often
fissured. These fissures can cause instability in excavated slopes

Sensitive Clays

The relation between liquidity index and saturated consistency depends on the sensitivity of the
clays. Sensitive clays behave very differently than insensitive clays. Sensitive clays are marine
deposited clays that have been leached of their salt content and glacial lake clays. Sensitive clays
usually have LI values >> 1

Sensitivity Definition

Sensitive clays become very weak when they are remolded. The definition of sensitivity is the
undrained strength of an undisturbed sample to that of a remolded sample at the same water content

Liquidity Index and Pc. Effective Overburden Pressure

Pc is the pressure that has acted on the clay sometime in its geologic history

See next page for estimate of Preconsolidation Pressure related to liquidity index.




                                                   8
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

Objectives

1. List parameters most often used to characterize coarse-grained soils

2. Use provided index data to estimate relative density of coarse-grained soils

3. Use correlations to estimate shear strength from relative density values

Characterizing Coarse-Grained Soils

Identify origin
Weathered Bedrock (Sandstone, etc.)
Residual
Colluvial
Alluvial
Glacial Till
Windblown

Characterizing Sands and Gravels

The most important factors are:
Gradation % sand, % gravel, and % fines
Gradation - Well graded and poorly graded
Mode of deposition
Angularity
Relative density

Identify Index Properties
1 - Percent Fines (% Finer than the #200 sieve)
2 - Percent Gravel (% Finer than 3”minus % finer than #4 sieve)
3 - Percent Sand (% Finer than #4 sieve minus % Finer than the #200 sieve % finer than)

Characterizing Sands and Gravels

Classify as Clean, Dirty, or Dual
       Clean is less than 5 % finer than #200 sieve
       Dirty is more than 12 % finer than #200 sieve
       Dual is 5 to 12 % finer (inclusive) finer than #200 sieve

For Clean Sands or Gravels, identify major constituent (Is there more sand or gravel?)

For Clean Sands or Gravels, identify whether poorly graded or well graded

Poorly Graded Sands and Gravels are either mostly one size particle, or they are gap-graded




                                                2
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils


Characterizing Sands and Gravels

Well Graded Sands and Gravels have a wide range of particle sizes and about equally distributed


Dirty Sands and Gravels should be evaluated for the plasticity of their fines.

Liquid Limit test performed on the portion of the total sample finer than the #40 sieve

Plastic Limit test performed on the portion of the total sample finer than the #40 sieve

Plasticity Index - The numerical difference between the Liquid Limit water content and the
Plastic Limit water content PI = LL - PL

Clean Sands and Gravels (< 5% fines)

Clean Poorly Graded Gravels GP
Clean Well Graded Gravels GW
Clean Poorly Graded Sands SP
Clean Well Graded Sands SW

Dirty Sands and Gravels ( >12 % fines)

Dirty Gravels with Plastic Fines GC
Dirty Gravels with Nonplastic Fines GM
Dirty Gravels with Hatched Zone Fines
GC-GM

Dirty Sands and Gravels ( >12 % fines)

Dirty Sands with Plastic Fines SC
Dirty Sands with Nonplastic Fines SM
Dirty Sands with Hatched Zone Fines
SC-SM

Dual Class Sands and Gravels
between 5 and 12 % fines, inclusive




                                                3
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

Example Class Problem - Given the following summary information, classify each sample

             % Finer                                  Well or Poorly
                                       LL      PI                           CLASS
  #200         #4             3"                         Graded
   4           89            100       NA NA               poor
   3           41            100       NA NA               well
   9          100            100       22 4                poor
   28          78             98       30 16                NA
   38          58             97       42 26                NA

Characterizing Coarse-Grained Soils Relative Density

Relatively clean, coarse-grained soils for the purposes of this discussion are sands and gravels
with very few fines, or with non-plastic fines, if the percentage of fines is significant. The
Unified Soil Classification System groups to which these discussions apply are primarily
SP, GP, SW, GW, SP-SM, GP-GM, SW-SM, GW-GM, SM, and GM.

The degree of compactness of these soil types may be described both qualitatively and
quantitatively in terms of relative density. In general terms, relative density of a coarse-grained
soil describes the relationship of the soil at its present density compared to its maximum possible
and minimum possible densities. The maximum and minimum densities of a coarse-grained soil
depend on the size, shape, and particle distribution of the soil. The relative density of soils may
be of interest when the soils are in compacted fills or in foundations of structures.

To illustrate this, consider the minimum and maximum possible densities for an entirely uniform
arrangement of spherical particles. In the loosest possible arrangement, the spheres rest directly
on the peak of the other spheres, and the porosity, or percent of total volume that is void space, is
47.6 percent. In the densest arrangement of particles, the spheres rest in the valleys between
adjacent spheres, and the porosity is reduced to 26.0 percent. These values are for hypothetical,
perfect spheres.

Coarse-grained soils in nature have a range of possible densities between about 75 and 145
pounds per cubic foot. Poorly graded, or very uniform, coarse-grained soils cannot exist in as
dense a condition as a similar, well-graded soil. In a well-graded soil, small particles occupy
void space between the larger particles, and a more dense soil results.

QUALITATIVE DESCRIPTION OF RELATIVE DENSITY:

To qualitatively describe the relative density of a sand or gravel deposit in the field, the
following guidelines are suggested. These descriptions may be implemented if surface methods
such as a backhoe trench or other method allow access to the soil. Visual examination plus very
simple field tests are the most basic way of evaluating relative density. If drilling methods are
available, following sections in this activity describe methods for quantifying relative density
descriptions more accurately.


                                                  4
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils


RELATIVE DENSITY
DESCRIPTION
                              EVALUATION PROCEDURE AND TYPICAL REACTION
                              A reinforcing rod can be pushed several feet into the soil.
VERY LOOSE
                              Corresponds to relative density of 0-15 %.
                              Can be excavated with a spade. A wooden peg 2 inches by 2
LOOSE                         inches can be easily driven to a depth of at least 6 inches.
                              Corresponds to relative density of 15-35 %.
                              No description available. Infer as between above and below
MEDIUM
                              descriptions. Corresponds to relative density of 35-65 %.
                              Requires a pick for excavation. A wooden peg 2 inches by 2
DENSE                         inches is hard to drive beyond six inches. Corresponds to relative
                              density of 65-85 %.
                              No description available. Infer from above definition of dense.
VERY DENSE
                              Corresponds to relative density of over 85 %.

QUANTITATIVE DESCRIPTION OF RELATIVE DENSITY:

If data is available from tests or estimates, relative density may be quantitatively
estimated as well as qualitatively. Quantitative definition of relative density is from the
equations that define relative density, covered below. A soil that is at a void ratio mid-
way between the maximum and minimum possible void ratios for the soil is at a relative
density of about 50 percent. The precise calculation of relative density uses an equation
derived from the classical equation for relative density, in terms of void ratio. From this
equation, another equation that is more useful can be derived, using terms of density
rather than void ratio. The equation relating relative density to the field density,
maximum index density, and minimum index density is follows:

                                         d max  dfield   min 
                            Rd (%)                                  100
                                        dfield  d max   d min 

This is illustrated in the following example. If a soil has a minimum index density of
92.0 pounds per cubic feet and a maximum index density of 112.0 pounds per cubic feet,
and if the soil deposit in the field has a measured dry density midway between these
densities, or at 102.0 pounds per cubic feet, the calculated value of Rd is:

                                   112 .0102 .0  92 .0
                        Rd (%)                           100  54 .9%
                                    102 112 .0  92 .0




                                                     5
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils


ESTIMATING RELATIVE DENSITY FROM MEASURED DENSITY AND
CLASSIFICATION:

If one does not know actual values of minimum and maximum index densities for a soil
being examined, a relative density percentage can be estimated if the dry density of the
deposit being evaluated is known. Chart 2 shows relationships between soils' in-place
dry unit weight and their relative density for two soil types. To determine the relative
density of a soil deposit using these curves, one must know the in-place dry unit weight
of the soil. Field density measurement techniques include the sand cone test, nuclear
density measurements, and others. This chart was developed in a study of soils for the
Alaska pipeline project. The correlations have considerable scatter and you should
realize that the estimate is very approximate.

EXAMPLE:

Given: A soil being examined is a silty sand field classified as SM. A field density test
is performed with a nuclear density meter, and the in place dry unit weight is determined
to be 102.5 pounds per cubic foot.

Find: What is the relative density, in percent, and in qualitative terms?

Solution: Using Chart 2, locate the band labeled "sand and silty sand". Using a value of
dry density of 102.5 on the vertical axis, read horizontally to the middle of the sand and
silty sand band, intersect, and read upwards to the relative density scale. Read a value of
relative density of about 60 %. Qualitatively, from a following table, this is a medium
relative density.




                                             6
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




                                     Relative Density Estimates for Two Soil Types

                      140



                      130



                      120                                                             Gravelly sand
   Dry Density, pcf




                                                                                                  sand and silty sand

                      110



                      100



                       90                         Reference - Donovan, N.C. and Sukhmander Singh, "Liquefaction
                                                  Criteria for the Trans-Alaska Pipeline." Liquefaction Problems in
                                                  Geotechnical Engineering, ASCE Specialty Session, Philadelphia, PA,
                                                  1976.
                       80
                            0   10    20     30          40         50           60        70         80        90      100
                                                           Relative Density, %

                                                              7
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




                                               Saturated water content versus Relative Density for Silty Sands (SM)

                                45


                                40


                                35
   Saturated Water Content, %




                                30
                                                                                                                      Average

                                25


                                20


                                15
                                         Reference ? Donovan, N.C. and Sukhmander Singh, "Liquefaction Criteria for
                                         the Trans-Alaska Pipeline." Liquefaction Problems in Geotechnical
                                10       Engineering, ASCE Specialty Session, Philadelphia, PA, 1976.



                                 5
                                     0    10          20         30          40           50            60      70          80   90   100
                                                                                  Relative Density, %


                                                                                    8
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




                                                              9
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

In the case of a drilled hole, obtaining a sample from beneath the water table may be
useful in back-calculating a dry unit weight. If one assumes that a sample obtained from
below the water table is saturated, then the dry unit weight may be calculated from the
equation:
                                                       water
                                        dry 
                                                 wsat (%)       1
                                                            
                                                  100           Gs
Where,

         Dry Density is in the same units as used for the unit weight of water. The unit
         weight of water is 1.0 grams per cubic centimeter or 62.4 pounds per cubic feet)

         wsat(%) is obtained from oven drying the sample, and

         Gs is the specific gravity of the soil solids
         (usually may be assumed to be 2.66)

EXAMPLE:

GIVEN: A deposit of field classified SM soil is investigated for the foundation of an
earth embankment. A sample is obtained from a depth of 10 feet, and the saturated water
content is determined to be 21.5 percent.

FIND: Estimate the relative density of this soil.

SOLUTION:

Step 1. Back-calculate the value of dry unit weight represented by the saturated water
content of 21.5 %, using the equation:

                                                             water
                                             dry 
                                                       wsat (%)       1
                                                                  
                                                        100           Gs

                                               62.4
                                   dry               105.6 lb 3
                                            21.5    1           ft
                                                 
                                            100 2.66




                                                  10
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

Step 2. Using Chart 2, read a relative density of 60 percent for the middle of the sand and
silty sand band. Alternatively, you could read directly from Chart 3, and you would read
from the 21.5 percent saturated water content to a relative density value of about 60
percent. Both Charts 2 and 3 will give the same answer because they are mathematically
related.

STANDARD PENETRATION TESTS:

Another means of assessing the relative density of coarse-grained soils is from results of
standard penetration tests. In a standard penetration test, a 140-pound weight is dropped
a distance of 30 inches onto a drill rod with a 2-7/8 inch diameter sampler on the end of
the drill rod at the depth of interest. The number of drops of the weight required to
advance the sampler a distance of 1 foot is recorded and is termed the N value for the
coarse-grained soil.

Relative density may be qualitatively described on the basis of standard penetration test
results as follows:

STP BLOW COUNT RELATIVE DENSITY
  0-4               Very Loose ( 0-15 % )
  4-10              Loose ( 15-35 % )
 10-30              Medium ( 35-65 % )
 30-50              Dense ( 65-85 % )
Over 50             Very Dense ( > 85 % )


Another way of estimating relative density values is to perform a one point
Standard Proctor Test on a sample of air dried sand. This procedure was developed from
a testing program at the Fort Worth laboratory. From the testing program, correlation
equations were developed. These equations allow you to estimate a value of 50 percent
relative density or one of 70 percent relative density from the field 1 point Proctor test.
Tests were performed on ASTM C-33 concrete sand gradations, commonly used as a fine
filter in drainage systems.

The equations developed by Fort Worth are:

       RD70 =         1.075 x d 1pt - 9.61, for RD70 and d 1pt in lb/ft3

       RD50 =         1.07 x d 1pt - 12.5, for RD50 and d 1pt in lb/ft3




                                            11
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




             125

             120

             115
   50 % Rd




             110

             105

             100

              95

              90
                   90      95            100           105           110         115   120   125   130
                                                        Field 1 pointdry density




                                                             12
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




                           130

                           125

                           120
   70 % Relative Density




                           115

                           110
                                                                                            Line of
                                                                                            Equality
                           105

                           100                                      Best Fit Linear
                                                                    Regression
                            95                                      Line for Data


                            90
                                 90   95   100        105           110               115          120   125   130
                                            Field 1 Point Proctor Test Dry Density, pcf




                                                             13
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

The way that one could use this information is as follows, illustrated with an example:

1. First, measure the in place dry density of the foundation. You could do this by a direct technique
   such as a sand cone or nuclear method. OR, you could measure the water content of a saturated
   sample. For example, say the measured dry density is 105.0 pcf (the saturated water content
   would be 21.8 %).

2. Second, take the sample and perform a 1 point Standard Proctor trial. For example, say the test
   measured a one point dry density of 108.5 pcf.

3. Estimate value of 50 % Relative Density using the above equation:

        RD50 =         1.07 x d 1pt - 12.5, for RD50 and d 1pt in lb/ft3

        RD50 =         1.07 x 108.5 - 12.5 = 103.6 pcf


4. One could also estimate a value for 70 percent relative density using the above equation:

        RD70 =         1.075 x d 1pt - 9.61

        RD70 =         1.075 x 108.5 – 9.61 = 107.1 pcf

5. The measured dry density of 105.0 pcf then is between the 50 % and 70 % relative density
   values. But, if one wants to have a more precise estimate of the relative density of the soil, the
   following procedure can be followed.

Knowing the value for 50% relative density is 103.6 pcf and the value for 70 % relative density is
107.1 pcf, you can write simultaneous equations from the relative density equation:

                                                 d max  dfield   min 
                                  Rd (%)                                    100
                                                dfield  d max   d min 

When you do this for the values in this example, as follows:


dfield = 105.0

50 % Rd = 103.6

70 % Rd = 107.1

Solving the relative density equations simultaneously, as shown on Attachment 1, you obtain an
estimated value for maximum index density of 112.8 pcf and an estimated value for minimum index
density of 95.7 pcf.




                                                       14
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

Substitute the value for measured field density given of 105.0, a value for maximum index density of
112.8, and a minimum index density of 95.7 into the relative density equation to calculate a more
precise estimate of the relative density of the soil:

               d max  dfield   min 
Rd (%)                                    100
              dfield  d max   d min 



              112 .8105 .0  95 .7 
Rd (%)                                100  58 .4%
              105 .0112 .8  95 .7 

The derivation of this procedures is shown below

          d m ax 103 .6   m in 
0.5 
        103 .6 d m ax   d m in 

51.8 dmax – 51.8 dmin = 103.6 dmax - dmax * dmin

-51.8dmax– 51.8 dmin = - dmax * dmin



          d m ax 107 .1   m in 
0.7 
        107 .1 d m ax   d m in 

75.0 dmax – 75.0 dmin = 107.1 dmax - dmax * dmin

-32.1 dmax – 75.0 dmin = - dmax * dmin

Then, because each term is equal to - dmax * dmin

-51.8dmax– 51.8 dmin = -32.1 dmax – 75.0 dmin
Combining terms,

19.7 dmax = 23.2 dmin

then,

            19.7
 d min           d max  0.849 d max
            23.2




                                                       15
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils


Substituting this into one of the equations:

-51.8dmax– 51.8 dmin = - dmax * dmin

-51.8dmax - 51.8(0.849dmax) =- dmax * 0.849dmax

-51.8dmax - 51.8(0.849dmax) = - 0.849dmax2

Combining terms, then,

0.849dmax2 - 95.78dmax = 0

From the quadratic equation, then

              b  b 2  4a  c
 d m ax 
                   2a

               ()95 .78   95 .78 2  40 .849  0
 d max 
                           2  0.849

dmax = 112.8

Then dmin = 0.849 x dmax = 0.849 x 112.8 = 95.7 pcf


      METHODS FOR ESTIMATING PERMEABILITY OF COARSE-GRAINED SOILS

Important Factors in Determining Permeability of Coarse-grained Soils

         Percentage of Fines. A figure on following pages shows how the presence of fines
         drastically reduces the permeability of coarse-grained soils. Permeabilities shown on the
         chart are for a coarse sand to which various amounts of clay and silt type fines have been
         added. The chart shows that clay fines reduce permeability more than silty fines. The chart
         is not useful as a design tool, but it does demonstrate quantitatively how the percentage of
         fines and the character of those fines affects the permeability of coarse-grained soils.

         Effective grain size (D10) The D10 size of a soil is the diameter of the particle size such that
         10 percent of the total sample, by dry weight, is smaller than this size particle. The value is
         obtained from a soil gradation curve plotted as percent finer versus sieve size or log of grain
         size as shown in figure 3. The data for plotting such curves is obtained from a gradation
         analysis, or mechanical analysis of a soil sample.

         In figure 3, read horizontally from 10 percent to intersect the gradation curve, read
         downwards to the scale at the bottom of the curve the D10 size for the soil using the scale in


                                                    16
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils


      millimeters. For the example soil number 1 shown in figure 3, read a D10 size of 0.18
      millimeters.

      Several empirical estimates have been developed based on correlations of permeability
      measurements and gradations of tested soils. These are discussed as follows.


             a. Hazen's equation.

             The following equation is based on experiments on relatively clean filter sands in a
             loose state. This chart is applicable only to soils that have a D10 size between 0.1 and
             3 millimeters. USCS classes can include SP, SP-SM, SW, and SW-SM. If the ratio
             of the D10 size to the D5 size of the sample is greater than 1.4, the estimate given by
             the equation will be too high.

                                            k, (fpd) = 2,835 x D102
                    Where,
                                    k is the coefficient of permeability, in feet per day
                                    D10 is effective grain size, in mm.

             For the example soil number 1 shown on figure 3 with a D10 of 0.18 millimeter,
             calculate an estimated permeability of 92 feet per day
             (3.25 x 10-2 cm/sec). For this soil, the ratio of D10 to D5 is 1.5. Since this ratio is
             above the maximum guideline given of 1.4, the estimate for this soil is probably high.

             b. Lincoln Filter Study

             The following equation was developed by the Lincoln NRCS soil lab in testing they
             performed on granular filter sands and gravels. It is applicable for these types of soils
             – clean sands and gravels that are not gap graded. The equation correlating
             permeability to D10 size is:

                                                 K = 992 x D102




                                                17
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

             c. Slichter's chart.

             These charts are developed for undisturbed soils. The charts, shown on figures 4A
             and 4B, correlate the permeability of soils with two factors; the D10 of the soil, and its
             dry unit weight. The ordinates of the charts are the dry density of the soil, in grams
             per cubic centimeter. The abscissas are the permeability, in feet per day. The charts
             have a series of curves for various D10 sizes of soils. Figure 4A is useful for soils
             that have a D10 size between 0.01 and 0.4 millimeters, while figure 4B is for soils that
             have a D10 size between 0.5 and 5.0 millimeters.

             Using example soil number 1 in figure 3, estimate the permeability of the soil
             assuming a dry density of 1.60 grams per cubic centimeter. With a D10 size of 0.18
             millimeters, read a permeability estimate of about 40 feet per day (1.41 x 10-2
             cm/sec).

      4. Estimates based on D20 size of soil.

      The chart shown in figure 5 correlates the D20 size, in millimeters, of soils with the
      coefficient of permeability, in feet per day. The chart is specifically for undisturbed, water
      deposited soils. To estimate the permeability of a soil using this chart, determine the D20
      size of a soil from its gradation curve, read vertically in figure 5 to the diagonal line, and read
      the left scale value for the coefficient of permeability. For example, using soil 1 in figure 3,
      with a D20 of 0.33 millimeters, read a coefficient of permeability of 80 feet per day (2.82 x
      10-2 cm/sec) using figure 5 .

      Because this chart is based on the D20 size and does not adequately consider the importance
      of the presence of any silt or clay fines in the soil, permeability estimates of the chart can be
      high. Permeability estimates should be regarded as probably high if the coefficient of
      uniformity (Cu) of the soil is greater than 5. Cu is defined as the D60 size, in millimeters,
      divided by the D10 size, in millimeters. Soils that have low Cu values are poorly graded, and
      usually more permeable than soils that have higher Cu values.

      For the soil 1 in figure 3, the calculated value of Cu is 5.6, and, therefore, the estimate
      obtained is probably slightly high.




                                                  18
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils

      Permeability Estimates – Slichter Method. The charts shown on a following page can be
      reduced to a single equation. The equation uses values of porosity (n) and D10 size to
      estimate a k value. Porosity n can be calculated if you know or assume a value for dry unit
      weight. The method for calculating n is as follows:

      First, calculate a value for void ratio given the assumed or know value for dry density as
      follows:

                                                    Gs   water
                                               e                1
                                                        dry

      Next, calculate porosity as follows:

                                                                      e
                                               n(decimal) 
                                                                     1 e

      Slichter’s equation then is as follows:

                                                         9.3071n
                             k ft          29.692  e             100     2
                                                                           D10
                                    day

      Where e = natural logarithm base




                                                    19
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




                                                        D10 size
                           0.01         0.10                             1.00    10.00
                                                                                     1.00E+02


                                                                                    1.00E+01


                                                                                    1.00E+00
    Permeability, cm/sec




                                                                                    1.00E-01


                                                                                    1.00E-02


                                                                                    1.00E-03


                                                                                    1.00E-04


                                                                                    1.00E-05

                                           Log K vs. Log D10 size


                                                             20
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils



                                                   Justin Hinds Craeger Chart


                1.00E+01


                1.00E+00


                1.00E-01


                1.00E-02
    k, cm/sec




                1.00E-03


                1.00E-04


                1.00E-05


                1.00E-06
                        0.00             0.01                     0.10           1.00   10.00
                                                           D20 Size, mm



                                                             21
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils



                                               Effect of Fines Content on Permeability

                                1000




                                100
   Permeability, feet per day




                                 10




                                  1




                                 0.1
                                       0   1     2         3           4           5      6   7   8
                                                         Percent Finer than # 100 sieve




                                                                22
NPEG – Geotechnical Engineering, Module 4, Characterizing Coarse-Grained Soils




                                Generalized Permeability Characteristics of Soils

cm/sec           100 10         1          10-1      10-2      10-3      10-4      10-5      10-6      10-7      10-8      10-9
ft/day       283,500 28,350     2,835      284       28        2.8       .3        .03       .003      .0003     .00003    3 e-5


Drainage                                Good                                     Poor                 Practically Impervious

                                                               Very fine sands, organic and inorganic
                                Clean Sands, Clean sand
                                                               silts, mixtures of sand silt and clay,       Impervious clays, I.e.,
                                and gravel mixtures
Soil Types     Clean Gravel                                    glacial till, stratified clay deposits, etc. homogeneous clays below
                                                                                                            zone of weathering
                                                     Impervious soils modified by effects of
                                                     vegetation and weathering

Reference - After Casagrande and R.E. Fadum




                                                             23
NPEG – Geotechnical Engineering, Module 5, Soil Mechanics Center Laboratories


Objectives

   1. Explain services of Soil Mechanics Center laboratories

   2. List sample size requirements for most commonly performed tests

   3. Explain methods for shipping samples to lab


INTRODUCTION

The Soil Mechanics Center laboratories at Lincoln, Nebraska, and Fort Worth, Texas, provide soil
testing services for the NRCS. The Soil Mechanics Centers have provided soil testing and design
recommendations for over 40 years, to the various programs of NRCS. The Soil Mechanics Center
laboratories are a resource you should consider in your CO-01 work. The laboratories use state-of-
the-art equipment and methods to assist with the design of sewage lagoons and waste storage
structures, as that type of structure begins to play a more important role in our Agency's emphasis on
water quality.

There is no direct reimbursement for tests or analyses performed by the Soil Mechanics Center
laboratories. Usually, test results on samples submitted for index tests only can be returned within a
short time after receipt of the samples, unless the laboratory has a backlog of workload. If more
complicated testing, including permeability tests of proposed clay liners is needed, you need to
coordinate with the laboratories to determine the current required turn around time. When
laboratories have a high backlog of testing requests, the time to complete requested testing may be as
much as 6 months. Ordinarily, and if a quick turnaround is needed, the turnaround time is less than
this.

Index Tests

Many engineers rely upon field classification to judge the preliminary potential for leakage at waste
water storage sites and lagoons. Many recommendations, such as those in Appendix 10D of the Ag
Waste Management Field Handbook rely upon accurate classifications of soils. It is especially
important to have a good idea of the percentage of fines in soils and the plasticity of the fines.
Laboratory tests are preferable to field estimates for these important properties. Index test data could
also be obtained on samples from a particular site to document a verification of field estimates. If
problems were to develop at a site, such documentation could be very valuable.

Laboratory tests on representative soil types from a given area can aid engineers and technicians in
developing experience in estimating these properties. It may be very worthwhile to submit samples
to the Soil Mechanics Center to have gradation analyses and Atterberg limit tests performed on
common soil types in a given area. A sample should be large enough to retain some of the soil at the
field office for future training. This sample, together with the data furnished by the lab, could then
be used to train others in the area and to maintain expertise in estimating these important soil
parameters.

Table 1 shows the size of sample you should submit to the NSMC laboratory for gradation analysis
and Atterberg limits.




                                                   1
NPEG – Geotechnical Engineering, Module 5, Soil Mechanics Center Laboratories

Compaction Tests

If a clay liner may be required for a site because of high permeability soils at grade, and local
sources of clay are available, samples of the clay source could be obtained and submitted for tests.
In addition to the normal index tests, the Soil Mechanics Center laboratory would probably
recommend performing Standard Proctor compaction tests to determine desirable placement
densities and water contents for the clay liner. Experience has shown the beneficial effect of
compacting clays at water contents several percentage points above optimum water content to
achieve the lowest possible permeability.

Refer to Table 1 for the size of sample the Soil Mechanics Center laboratories need to perform
compaction tests.

Permeability Tests

If the permeability of a proposed clay soil to be used for a liner is in question, permeability tests may
be performed on samples of the clay compacted to different degrees of Proctor density, at various
water contents. Permeability tests might be performed, for instance, at densities of about 90 percent
and at 95 percent of maximum Proctor density, at a water content 2 percent wet of optimum. Based
on results of these tests, one could decide whether special compaction equipment such as tamping
rollers would be required to construct a quality liner.

Permeability tests may also be requested when local clay sources are not available, and soils at grade
at the site are excessively permeable. Often, bentonite treatment of the soils at grade can provide a
greater assurance of protection against excessive leakage. The Soil Mechanics Center laboratories
can perform permeability tests on sandy soils with various amounts of bentonite to determine the
minimum amount needed to achieve the desired permeability.

Refer to Table 1 for recommended sample sizes. L size samples are needed if compaction tests are
requested.

PROCEDURES FOR SUBMITTING SAMPLES

The Lincoln laboratory performs normal testing for the Northeast, Midwest, Northwest, and
Southwest Regions. The Fort Worth laboratory performs testing for the South Central and Southeast
Region States.

Large samples may be shipped to the Soil Mechanics Centers by normal truck freight lines. To ship
large samples by US mail, FedEx, or UPS, you can split large samples into several smaller samples
for shipment. Address samples to:

Soil Mechanics Laboratory              or     Soil Mechanics Laboratory
Building 23                                   512 South 7th Street
Fort Worth Federal Center                     Lincoln, NE 68508
501 Felix Street
Fort Worth, TX 76115




                                                    2
NPEG – Geotechnical Engineering, Module 5, Soil Mechanics Center Laboratories

 Methods for labeling and tagging samples for shipment to the Soil Mechanics Center are important.
Using indelible ink on paper tags and writing on plastic bags with permanent ink felt tip markers are
methods of labeling samples that ensure easy identification by the laboratories. It is always wise to
have redundant labeling, with a sample tag inside the bags as well as having the outside of the bag
labeled. You should submit with the sample shipment a sample list. Table 2 below is an example of
a format for a sample list to submit with sample shipments. This is needed so the Soil Mechanics
Center can check that all samples submitted are actually received, and for our record keeping
procedures. The Soil Mechanics Center labs each receive 1,000 samples per year, and standardized
procedures for labeling and identifying samples are required to prevent errors.

Include a copy of a letter detailing the tests requested, sample and site identification information.
Also include a name and address to contact with any questions, and names and addresses of those to
receive a copy of the test report with the shipped samples. A copy of this information should also be
mailed separately from the sample shipment. Copies of the letter may also be sent to those who
should be aware of this activity administratively.

Sturdy plastic bags of at least 8-mil thickness should be used for the samples. This prevents bag
rupture and spillage during shipment. If thinner bags are used, double the bags. You should use
sturdy corrugated paper boxes with reinforcement tape at the seams for shipping.

Summary of Procedures for Submitting Samples to Soil Mechanics Center Laboratories

1. Prepare a Sample List showing field sample number, depths, and size of samples.

2. Prepare a letter detailing what kinds of tests are requested, the name and phone number of a
contact person, addresses and names of those who should receive a copy of Soil Mechanics Center
reports, and project name and identification information.

3. Send a copy of the letter and sample list to the Soil Mechanics Center separately from the sample
shipment. Also includes copies with the sample shipment. Send copies of the transmittal letter to
any one who should be aware of this activity administratively.

4. Pack samples carefully to protect from damage during shipment and send to above address.




                                                  3
NPEG – Geotechnical Engineering, Module 5, Soil Mechanics Center Laboratories

TABLE 1 - SUGGESTED SIZE OF SAMPLES FOR SOIL MECHANICS TESTS

Introduction

The size of sample you need to submit depends mainly on two things:

       (1) What tests you are requesting, and

       (2) The amount of gravel in the sample and the size of any gravel particles in the
        sample.

If you are submitting samples only for index tests, gradation and Atterberg limits, you need to send a
sample size designated "S" in Table 1.

If you are requesting compaction tests and/or permeability tests using bentonite, you should send a
sample size designated "L" in Table 1. The Soil Mechanics Laboratories often receive samples that
are too small for the requested tests to be performed, and you should be sure to obtain sufficient
quantity of soil for the requested tests.

                                                TABLE 1

DESCRIPTION OF              LARGEST                    TYPE          MINIMUM
GRAVEL IN                   SIZE GRAVEL                OF            SAMPLE
SAMPLE                      IN SAMPLE                  SAMPLE        SIZE (lbs)

Sample has less                  < 3/4 "                "S"             1
than 10 % gravel                   3"                   "S"            10
                                   3"                   "L"            50

Sample has over                    3"                   "S"            20
10% but less than                                       "L"            75
50 % gravel

Sample has more                    3"                   "S"            40
than 50 % gravel                                        "L"            100




                                                   4
NPEG – Geotechnical Engineering, Module 5, Soil Mechanics Center Laboratories


              TABLE 2 - SAMPLE LIST FOR SOIL MECHANICS CENTER

STATE:____________        SITE NAME: ___________________________

CONTACT PERSON: ________________ PHONE: _____________________

      FAX: _______________________
Laborator    Field
y Sample     Sample                                                  Depth,     Size of
Number       Number        Description or Location                   (feet)     Sample




                                              5
NPEG – Geotechnical Engineering, Module 6, Compaction


Objectives

1. Outline the procedures for performing standard compaction tests
2. Explain the role of compaction testing and field density testing in sampling, design,
   and construction quality control of earth fills
3. Explain the difference between quality control and quality assurance

Introduction. The coverage of compaction of soils in this introductory course is very
brief and cursory. If you will be involved in compacting soils and using testing to verify
the adequacy of compacted fill, it is essential that you complete more thorough training in
compaction.

In a National Bulletin, Number 360-9-74, dated July 5, 1989, the NRCS Director of
Engineering strongly suggested that all project engineers and construction engineers
complete Soil Mechanics Module 5 on Compaction. A prerequisite to this Module is
Module 4 on volume-weight relationships.

The Bulletin suggests reviewing the course material about every 5 years to ensure
retention of the technical points in the training.

Completing this module will take about 1 week of uninterrupted time to be set aside for
this purpose. This bulletin strongly suggests that supervisors set aside time for this
purpose if the training is needed for an employee.

You will also find the information in these modules very helpful if you will be involved
in construction of clay liners in waste storage facilities. Knowledge of the principles of
compacting soils is basic to many NRCS projects.

Definitions. Compaction is the mechanical densification of a soil mass. It involves
applying physical forces to a soil to drive air from the soil. The result is a more dense
mass. Usually, unless the soil has few fines, very little water is expelled from the soil
during compaction. In constructing earth fills, soils are usually borrowed from one
location, transported to another location, and the soils are then compacted in the new
location. Sometimes, soils are compacted in place. The soils are disced, water content
adjusted as needed, and then compaction equipment is operated on the prepared soils.

Basic Principle of Compaction. The basic principle of soil compaction, developed by
R.R. Proctor, is that for a given energy, if a given soil is compacted at different water
contents, the resulting dry density of the compacted soil will vary. Because at very dry
water contents, the particles are not lubricated and are difficult to rearrange, the dry
density of soils compacted at low water contents is low. At high water contents, the
presence of so much water between the soil particles interferes with compacting the soils.
Because water is incompressible, the energy is not effective in rearranging the soil
particles into a more dense mass, and the compacted density is low then. In summary,
then, the principle can be illustrated with the following sketch:


                                           1
                                NPEG – Geotechnical Engineering, Module 6, Compaction



                                                                                          At intermediate water contents, the
                                                                                          highest densities result
Compacted Dry Density, lb/ft3




                                                                                                               At high water contents,
                                                                                                               low dry densities result




                                                                 At low water contents, low dry densities
                                                                 result




                                                           Water Content, Percent


                                Purposes of Compaction. Soils are compacted to produce a uniform fill with
                                predictable engineering properties. The engineering properties of the compacted fill are
                                affected by the degree of compaction (density) and the water content at which the
                                compaction is done. Compaction may have both desirable and undesirable results,
                                depending on the purpose of the earth fill. The following table summarizes how the
                                increased density resulting from compaction affects engineering properties of soils, and,
                                generally, whether the effect is desirable or undesirable. The judgement of whether an
                                effect is desirable or not is based on constructing an earth fill for a water impounding
                                structure such as a small earth dam. If soil were compacted for another purpose, such as
                                a road base, these judgements might be different.

                                                  Effect of Higher Densities on Engineering Properties

                                Property              Effect of Higher Density                    Beneficial/Detrimental
                                Shear Strength        Increases                                   Beneficial, especially for
                                                                                                  fills over 20 feet high
                                Compressibility       Decreases                                   Beneficial
                                Permeability          Decreases                                   Beneficial
                                Flexibility           Decreases                                   Detrimental
                                Shrink/Swell          Increases Swell Potential                   Beneficial
                                                      Decreases Shrinkage Potential               Beneficial

                                             Effect of Higher Water Contents on Engineering Properties



                                                                            2
                        NPEG – Geotechnical Engineering, Module 6, Compaction


                        Property           Effect of Higher Density             Beneficial/Detrimental
                        Shear Strength     Decreases                            Detrimental, especially for
                                                                                fills over 20 feet high
                        Compressibility    Increases                            Detrimental
                        Permeability       Decreases                            Beneficial
                        Flexibility        Increases                            Beneficial
                        Shrink/Swell       Decreases Swell Potential            Beneficial
                                           Increases Shrinkage Potential        Detrimental

                        Compaction Curve for constant energy
Compacted dry density




                                                At high water contents and
                                                low densities, structure is
                                                puddled or dispersed


                                              At low water contents and
                                              high densities, structure is
                                              flocculated



                                              Compacted water content




                                                                  3
NPEG – Geotechnical Engineering, Module 6, Compaction

Equipment. A variety of equipment may be used in compacting an earth fill. Strictly
speaking, only one piece of equipment that is used to actually compact the soil is the
compaction equipment. However, other auxiliary equipment is important to compact
soils properly. These other equipment used may include:

   1) A water wagon with sprayer bar
   2) A disc, usually a tandem type, for mixing soils and bonding successive lifts, as
      well as blending water into soils.
   3) A grader for smoothing out dumped soil to have lifts of soils about the same
      thickness.
   4) A transported used for carrying soils from the borrow area to the fill. May be
      scrapers (usually) or loaded dump trucks, etc.

NRCS Specifications. The standard specification in NRCS procedures is 23. This
standard recognizes 3 different classes of compaction. They are classes A, B, and C.
These methods for specifying fill placement are discussed as follows:

Class C (Method Specification). This class of compaction specifies the type of
equipment that will be used to compact the soils, and how the equipment will be
operated. The specification does not require any minimum density to be obtained so long
as the equipment is used as specified. It is always used when soils are difficult to test, or
where experience has shown that the specification produces acceptable fills. An example
specification is:

Using a maximum loose lift thickness of 9 inches, compact each layer of fill by at least 4
passes of a rubber-tired roller with tire inflation pressures of 60 to 80 psi, having a wheel
load of between 18,000 and 25,000 pounds. A minimum water content of 10 percent is
required on the mass.

Reference Test Specification. (Class A Compaction) This method of specifying soil
compaction is used for soils with less than about 25 percent gravel. The specification
requires a soil be compacted to a percentage of a reference test maximum density, at a
water content range referenced to the reference test optimum water content. Every
significantly different soil type at a fill project must be tested to determine the values of
maximum density and optimum water content to use this specification. NRCS uses the
Standard Proctor, ASTM D698 test method for most of its earth fill projects. Many earth
fills constructed for road foundations and building foundations are referenced to the
Modified Proctor, ASTM D1557 test.




                                            4
NPEG – Geotechnical Engineering, Module 6, Compaction

The engineer responsible for designing the earth fill selects the appropriate control test
and the degree of compaction, or percentage of maximum density required for the fill
compaction. The selection is based on previous favorable experience and engineering
property tests performed in a laboratory. Because the compaction water content as well
as the compacted density determine the engineering properties of the fill, a specification
will also contain a minimum and maximum acceptable water content for the fill.

Reference Tests – ASTM D698 (Standard Proctor) R. R. Proctor, a California
engineer in the 1930’s developed his theory of soil compaction. Simple stated it is that:

   Using a constant energy to compact a given soil, if the water content is varied, the
   resulting dry density of the compacted soil will vary. A plotted curve of dry density
   versus water content has a parabolic shape.

Test Methods. Three variations of the Proctor test are available, depending on the gravel
content of the soil being compacted. The most frequently used method is Method A used
for soils with less than 20 percent gravel content (less than 20 percent of the soil is gravel
particles, larger than the #4 sieve, by dry weight). This is Method A, and will be the only
method covered in this review.

Compaction tests are difficult to perform on sands with a low fines content because they
do not readily absorb and retain water. Obtaining test results over a range of water
contents is difficult. Usually, compaction tests are not performed on sands with less than
12 percent fines (minus #200 sieve). A single Proctor test on an air-dry sample may be
used to obtain a reference density. Relative density tests are also used, but time does not
permit coverage of this subject. See Module 5 for details.




                                            5
NPEG – Geotechnical Engineering, Module 6, Compaction

Standard Proctor Test Procedure. Usually, 5 separate samples of a soil are prepared by
first removing any plus #4, or gravels from the sample. Each sample weighs about 2,000
grams dry.

1.     The samples are moistened by spraying with water to 5 increasing water contents.
       Experience is required to determine the range of water contents used, based on the
       appearance and feel of the soil. Each specimen is about 2 percent wetter than the
       previous specimen.

2.     The specimens are allowed to cure for a period of time dictated by the clay
       content of the soil. Soils with a high clay content should be cured overnight
       before performing the test. Soils with a low clay content can be tested more
       quickly.

3.     Each sample of soil that has been prepared is compacted into a steel mold that is
       about 4 inches in diameter with a volume of about 1/30 a cubic foot. The soil and
       mold are weighed, and the wet density of the sample calculated. A representative
       water content specimen is obtained from the compacted sample, and an oven dry
       water content test is performed on the sample. The dry density of each specimen
       can then be calculated from the known values of wet density and water content.

4.     The results of the test are used to plot a curve with water content as the abscissa
       (X coordinate) and the dry density as the ordinate (Y coordinate). If correctly
       performed, the curve obtained by connecting the 5 test specimen values will be a
       parabolic curve.

5.     The peak dry density from the curve is interpolated and reported to the nearest 0.5
       as the maximum dry density for the soil. The value of water content at which the
       peak density occurs is interpolated to the nearest 0.5%, and reported as the
       optimum water content for the soil.

6.     In the D698 test, specimens are compacted into the mold in 3 lifts. Each lift is
       compacted with 25 drops of a 5.5 pound hammer, dropped 12 inches each time.
       The total energy applied to the specimen is 12,375 foot pounds per cubic foot.

7.     In the D1557 test, specimens are compacted into the mold in 5 lifts. Each lift is
       compacted with 25 drops of a 10 pound hammer, dropped 18 inches each time.
       The total energy applied to the specimen is 56,250 foot pounds per cubic foot.

8.     After plotting the results of the compaction test, the next important step is to draw
       a saturated water content versus dry unit weight curve. This is also called the zero
       air voids curve. The steps are as follows:

       a) Examine the range of dry densities from the plotted test and assume three
          values of dry density in the range, example 90, 95, and 100 pcf.
       b) Assume a specific gravity value or use lab test values


                                           6
                  NPEG – Geotechnical Engineering, Module 6, Compaction

                         c) Calculate wsat(%) for each assumed value of dry unit weight
                  Tabulate as follows:
                  Assumed Dry Unit Weight                     Calculated Value of wsat




                                                                 Optimum
                                                                 Water %
Dr density, pcf




                        Maximum
                        Dry                                                               Zero air
                        Density (pcf)                                                     voids curve




                                    Compaction curve




                                                          7
NPEG – Geotechnical Engineering, Module 6, Compaction

Evaluating a Compaction Test. It is important to evaluate the reasonableness of the
data and the quality of the test performed. Strict adherence to ASTM procedures is
required to obtain repeatable data. Following are suggestions for you to follow in
evaluating your completed test.
1.     Does the plotted curve have a smooth parabolic shape?

2.     Construct a zero-air-voids or saturated water content versus dry density curve to
       assist in the next evaluations. See handouts for equation to use.

       a.     Is optimum water content about 80 percent of saturated water content at
              the maximum dry density? The acceptable range is 70-90 percent.

       b.     Determine by using the maximum dry density in the saturated water
              content equation:
                                                 1 
                        wsat (%)  100   water     
                                           dry   Gs 
                                                     

       c.   Compute % saturation using optimum water content:

                      % Saturation at Optimum = wopt  wsat x 100

                       Water content, %


       d. Most Standard Proctor compaction tests will have a percent saturation value
          of about 80 percent – the line of optimums. Rarely is optimum water content
          less than 70 percent saturation and rarely is it greater than 90 percent.

       e. The wet side of a compaction curve will have water contents that are about 90
          percent saturated, for Standard Proctor curves.

       f. Are points on the curve about 2 percent apart in water content, with at least 2
          points dry and 2 points wet of optimum water content? This is required to
          interpolate optimum water content.




                                          8
NPEG – Geotechnical Engineering, Module 6, Compaction


3. Evaluate the reasonableness of the results, compared to similar soils. See Handouts
   for typical results for various soil types. Also, estimate values from following
   equations for CL, CH, and MH soils.

                      d max = 130.3 –0.82* LL + 0.3* PI

                      wopt (%) = 6.77 + 0.43* LL – 0.21* PI

                                                                      Is optimum water %
                                                                      equal to 80%
                                                                      saturated water
                                                                      content?




                                                                                      90% sat ?




                                   2 % apart ?




                                          9
NPEG – Geotechnical Engineering, Module 6, Compaction

                                            REFERENCES

http://www.dot.state.oh.us/construction/OCA/Manuals/default.htm
Compaction Manuals from Ohio Highway Department

http://www.ircmg.com/roadmachinery/compman/compman.html
Compaction manual from Ingersoll Rand manufacturer of compaction equipment

http://www.specialtysalesllc.com/nutra-bond_compaction.htm
Compaction manual from Caterpillear Company

http://www.usace.army.mil/inet/usace-docs/eng-manuals/em.htm
Engineering Manuals from the Corps of Engineers – See Manual 1110-2-2302 on design and construction
of earth fills.

http://www.efdlant.navfac.navy.mil/lantops_15/ - When you go to this page, search for Design Manuals –
soil mechanics – excellent reference from the Navy

                                           REFERENCES

http://www.dot.state.oh.us/construction/OCA/Manuals/default.htm
Compaction Manuals from Ohio Highway Department

http://www.ircmg.com/roadmachinery/compman/compman.html
Compaction manual from Ingersoll Rand manufacturer of compaction equipment

http://www.specialtysalesllc.com/nutra-bond_compaction.htm
Compaction manual from Caterpillear Company

Corps of Engineers Engineering Manual on Design and Construction of Earth Fills:
http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-2300/toc.htm




                                                10
NPEG – Geotechnical Engineering, Module 7, Problem Soils


OBJECTIVES

   1. List major categories of problem soils

   2. Use index properties to identify problem soils

   3. Identify typical distress to engineering structures caused by problem soil
      categories

INTRODUCTION
Many problems with NRCS sites are caused by unusual soils types. If one of these soil
types may be present at a planned site, special designs may be needed. Investigations
should be more intensive, and analysis more detailed when a problem soil type is
involved. The soil types covered below have been responsible for many of the soil
mechanics-related deficiencies and problems in the Natural Resources Conservation
Service Watershed and CO-01 programs.

                                 COLLAPSIBLE SOILS

Introduction

Definition. Collapsible soils are soils that undergo large settlements when saturated after
loading. Most normal soils will settle gradually as load is applied, and saturation does
not produce large additional settlements. Collapsible soils have a structure that allows
them to support loads in a moist condition. But, when saturated, the structure collapses,
and large settlements occur rapidly. This causes cracking of overlying embankments or
concrete structures.

Recognition. Collapsible soils are typically low density, low water content soils of CL,
CL-ML, and ML classifications. Some SC, SC-SM, and SM soils may also be
collapsible. Often these soils are windblown or alluvial fan deposits. Several charts have
been developed by correlation of index properties to collapse properties. Attachment 1 is
a Bureau of Reclamation chart. The chart is a plot of the ratio of in place dry unit weight
to the maximum Standard Proctor dry unit weight versus optimum water content minus
natural water content. If a soil plots to the right, significant collapse potential can be
expected. Attachment 2 is a plot of in place dry unit weight versus liquid limit. If a soil
plots in the collapse prone zone, problems can be expected.

To use either of these charts, the soil's in-place dry unit weight, water content, and liquid
limit are required. To use Attachment 1, a compaction test, or estimated compaction test
results are also needed. In-place density may be measured by a number of methods
including nuclear density meters, sand cone test, clod tests, and others.




                                              1
                        NPEG – Geotechnical Engineering, Module 7, Problem Soils

                        Design measures. Two approaches have been used in designing structures founded on
                        collapsible deposits. If the deposits are relatively shallow, the usual approach is to
                        excavate the deposits from beneath the planned structure. In cases where the deposits are
                        quite deep, the collapsible soils have been irrigated by one scheme or another, so that
                        settlement will occur as load is added, and not at saturation at a later time.


                                 Gibbs and Bara Evaluation of Collapse Potential


                                                               Liquid Limit
                        20           25          30            35         40           45          50           55
                   70


                             Collapsible
                   75



                   80



                   85
Dry Density pcf




                   90
                                                                                            Not Collapsible


                                                 94.224
                   95



                  100

                                                      102.96

                  105



                  110



                  115




                                                                    2
                NPEG – Geotechnical Engineering, Module 7, Problem Soils




                                               Collapse Potential - BUREC Chart


                100%


                             Collapsible Potential
                               Not Significant

                95%
                                                                                       4.73




                90%
Density Ratio




                85%                                                                     5.09




                80%




                75%
                                                                                  Collapsible Potential
                                                                                       Significant



                70%
                       -12                -7                -2                3                8
                                                            wopt - wnatural

                                                                 3
NPEG – Geotechnical Engineering, Module 7, Problem Soils


                                     SOFT CLAYS

Recognition. Soft cohesive soils may be recognized on the basis of "rules-of-thumb"
descriptions as given on Attachment 8, if the deposits are saturated at the time of
investigation. They may also be recognized on the basis of standard penetration tests, if
that equipment is available. A field torvane device ( demonstrated ) is also helpful.
Attachment 8 also shows typical blow counts and cohesive parameters for various
consistency clays. If dry unit weights and Atterberg limit test values can be obtained for
the soils, the saturated consistency may be evaluated as detailed in the Cohesive Soils
Handout for this Course.

Problems. The most likely problem with soft cohesive soils is the problem of excessive
settlement, and even sudden shear-type failure of the foundation as load is added to the
deposit. Structures such as oil storage tanks and grain silos have failed when suddenly
filled when soft and/or sensitive clays were present in foundations. Failure of earth
embankments during construction is a common problem on very soft clays. Long term
settlements may be excessive. If thickness of the deposits are uneven beneath a structure,
differential settlement aggravates the problem. This may occur where bedrock has a
sharp profile, or where alluvial deposition is uneven. The total magnitude of settlement
may be excessive, even if differential settlement is not a problem. Some buildings in
Mexico City have experienced settlements so great that formerly second stories are now
at ground level. Parts of Mexico City are constructed over very soft lake deposits.

Design Approaches. Several approaches have been used. One common approach in
highway work, where a compacted embankment is constructed across a deposit of very
soft clays, is to install sand and wick drains. These drains accelerate the speed of
consolidation. The use of wick drains constructed of geocomposites has largely replaced
the use of sand drains. Preloading the foundation is another approach, often used in
conjunction with sand or wick drains. Removal of the soft soils is an alternative where
the depth of the deposits is not excessive. Very slow loading has been used in some
instances. For severe conditions, penetrating the soft horizon with piles and founding the
structure on a firmer underlying strata is the only feasible measure. Other special
remedial techniques have been developed in recent years, including jet grouting to form
piles, etc.




                                             4
NPEG – Geotechnical Engineering, Module 7, Problem Soils


                                 DISPERSIVE CLAYS.

A section of this module concentrates on dispersive clays. This section covers
recognition, field and laboratory tests, and design problems. Where they occur,
dispersive clays cause many problems with NRCS structures. See Soil Mechanics Note
13 for more discussion.

LOOSE COARSE-GRAINED DEPOSITS

Recognition. Loose sands and gravels are characterized by low blow counts in the
standard penetration test. This test is the most commonly used method of investigation
and correlation when substantial foundation deposits of sands occur. When standard
penetration tests are not available, empirical charts may be used which correlate in-place
unit weight to relative density terms. Loose coarse-grained soils typically have relative
density values of less than 50 percent. Attachment 3 is useful for estimating relative
density of foundations when results of standard penetration tests are available. Use of
this chart was also covered in the Cohesionless Soils Handout of this Course. Other field
tests, such as the cone penetrometer may be useful in correlating deposits.

Problems. Loose coarse-grained deposits may have a high settlement potential. In
seismically active areas, liquefaction during an earthquake may be a serious problem.
The most susceptible soils are very fine, relatively clean loose sands. Loose sands and
gravels will have higher permeabilities than more dense deposits.

Design. Loading loose deposits will cause them to consolidate and gain strength. This is
a practical approach if the overlying structure can tolerate the settlement as the load is
added. If settlements are unacceptable, pre-loading may be one approach that is
workable. A load is added to the deposits, causing them to consolidate and improve.
This load is regarded as temporary, and when the settlement is completed, the surcharge
load is removed and the final structure built.
Another approach that is practical when these deposits are relatively limited in depth is to
remove or excavate the deposits from beneath the planned structure.

In some situations, special techniques for in-place improvement of loose, coarse-grained
deposits have been used. Very heavy weights can be dropped from heights, and the
impact of the weights vibrates and densifies the loose deposits. Special vibratory probes
can be inserted into loose coarse-grained, clean soils to densify them in-place.
Controlled, spaced blasting has also been used to accomplish the same purpose.




                                             5
NPEG – Geotechnical Engineering, Module 7, Problem Soils


                                  EXPANSIVE CLAYS

Recognition. Expansive clays are readily identified on the basis of their Atterberg limits
and percent of clay-size particles. Attachment 4 shows one grouping of soils based on
Plasticity Index and Percent Finer than the 0.002 mm size. Soils are rated as very high to
low in shrink-swell potential. Note that in using this chart, a value is calculated for
Activity of the clay. This definition of Activity is not the traditional definition, but is
used because in this study a better correlation was obtained. Attachment 5 shows another
classification system for classifying the shrink-swell behavior of soils based on the
percentage of 0.002 mm size particles and the PI of the soil.

Problems. Expansive soils probably cause more monetary damage to engineered
structures than any other group of problem soils. Most of this damage is due to
movement of foundations of light buildings, such as residences. The damage is caused
by the differential movement of a foundation caused by moisture migration from beneath
the covered foundation area. Attachment 6 illustrates how building damage occurs in two
situations. Attachment 7 summarizes a study which indicated the importance of trees in
affecting the water content of soils beneath concrete foundations, contributing to
damages.

Another type of problem common to expansive types of clays is the failure of excavated
and compacted slopes in these types of soils. On a long term basis, these types of soils
will develop a highly blocky structure which has very low shear strength. Design of
slopes on the basis of residual effective phi parameter dictates slopes from about 3.5 to 1
to perhaps 8 to 1 flatness.

Pipelines embedded in expansive clay backfills have collapsed from pressure exerted by
swelling expansive clays.

When used as backfill around concrete structures, especially against retaining walls, there
is almost no way to prevent movement of the structure when the expansive clays swell.
Shrinkage during prolonged droughts also produces unwanted movement of structures in
contact with expansive clays. If at all possible, alternate sources of backfill should be
located.

Design Measures. Prevention of movement under concrete structures involves two
approaches. One approach is to construct the concrete structure so strong that it can
support itself in a cantilevered situation. Post-tensioned reinforcement of slabs, highly
reinforced slabs with beams included are several methods used. The other approach is to
install a moisture barrier to prevent moisture movement from beneath the slab. This is
more workable when the initial water content condition of the foundation is very moist.
If the initial water content of the foundation clays is very dry, it will be much more
difficult to provide an effective water barrier. Drainage would be required in addition to
a water barrier. In addition to moisture barriers, limiting high transpiration vegetation
from the proximity of the structure is advisable. Attachment 7 shows results of a study
on slab movements related to height of trees.



                                             6
NPEG – Geotechnical Engineering, Module 7, Problem Soils

Another commonly used method of dealing with expansive clays is to treat the clays with
hydrated lime. The hydrated lime is thoroughly mixed with the clay, usually at the rate of
about 4 to 6 percent, by dry weight; water is added to promote curing; and the treated soil
is then compacted. The lime treated soils will have a plasticity index usually about 1/2 of
the untreated soil.

                     HIGH SOLUBLE SALT CONTENT SOILS

Recognition. Soils with a high naturally occurring salt content are found mostly in the
arid Western United States. The soils are easily recognized on the basis of conductivity
measurements made on saturated pastes or on solutions. Salty soils will have a much
higher conductivity than normal soils. Using a 1:20 solution of soil/water, SCS labs have
found that resistivity meter readings of less than 5,000 ohms-centimeter indicate a
probable salt content of greater than 0.5 % by dry weight. Gravimetric tests are used to
more precisely define the salt content if higher values are encountered. Very salty soils
commonly have a light color. Soils with more than about 5 to 10 percent by weight of
soluble salt content are usually regarded as undesirable in water impounding fills.

Problems. When used to construct impounding fills, such as dikes, diversions, or
embankments, soils with a high soluble salt content have the potential to lose their
integrity if impounded, fresh water dissolves out significant amounts of the salt in the
soil. Voids created could result in subsidence of the fill, and of the foundation on which
the structure is founded.

Design Approaches. The most common design approach to soluble salt soils is to avoid
their used in compacted fills. Usually, an investigation can delineate the area of high salt
content soils, and they can be avoided in the construction of the planned fill. Irrigation
with low salt content water could possibly used in some situations to leach salts out of a
foundation prior to construction. However, this has not been a commonly used method.

                         LOW PIPING RESISTANCE SOILS

Recognition. Soils with very low piping resistance are recognized primarily on the basis
of Unified Soil Classification System grouping, gradation, and Atterberg limit. Dry unit
weights may also affect the piping resistance of some soils. Soils groups with the lowest
piping resistance are fine, poorly graded sands with a low fines content and non-plastic
fines. USCS groups included are SP and SP-SM, and SM soils with less than 20 percent
fines which are non-plastic. The sands with lowest piping resistance have no coarse sand
or gravel fraction. Most of the sample is finer than the number 60 sieve.

Non-plastic silts classifying as ML also may be very low in piping resistance. These soils
will have a high percentage passing the #200 sieve, and a low clay content.




                                             7
NPEG – Geotechnical Engineering, Module 7, Problem Soils

Problems. Soils with a low piping resistance cannot withstand hydraulic gradients
imposed by stored water or water under artesian heads, or groundwater flow. Boils
develop under low heads in seepage exit areas. Continued flow of water results in
movement of soil particles from beneath structures, leading to undermining of the
structures or tunnels in foundations.

Another problem in these types soils is the sloughing of excavated slopes due to
groundwater flow to the excavation. This problem is analyzed with infinite slope
equations. Using typical values of effective phi parameters, stable slopes with seepage
exiting the slopes are typically from 3-1/2 to 4:1.

Designs. Two approaches are used to design against piping. One approach is to interject
a seepage barrier of soil or other material which will consume the head causing piping.
Increasing the length of flow paths is another approach. The second approach is to install
a properly designed filter at the point of seepage exit. The filter allows passage of the
seepage water and dissipation of the pressure without particle movement. Graded filters
and geotextiles both are used successfully.

                                   CALICHE SOILS

Recognition. Caliche soils are common to arid and semi-arid regions. The term refers to
soil layers in which the grains are cemented together by carbonates. The cementing
material is usually calcium carbonate, but may contain magnesium, silica, or gypsum.
Calcium carbonate will fizz strongly when dilute hydrochloric acid is applied. The soils
are characterized by a very light color, and are usually hard and cemented in appearance.

Problems. Thick, hard layers are difficult to excavate. The relative ease of compaction
is difficult to predict. Compacted soils are usually brittle. Recent deposits may be
collapsible.

Design. Testing of these soils must use special procedures. Due to hydrated minerals,
drying must be done at 60 degrees Centigrade rather than 110 degrees. Correlation with
field performance often gives the best indication of predicted performance.




                                            8
NPEG – Geotechnical Engineering, Module 8, References


Types of Geotechnical References

      NRCS Documents
      Other Federal Agencies
      Corps of Engineers Engineering Manuals
      Bureau of Reclamation Manuals
      TADS Modules
      NAVDOCKS DM7
      FERC and FEMA
      Internet Searches
      Google.com Others
      ASCE Journal Geotechnical Engineering
      ASTM Standard Test Methods
      ASTM STP’s
      Text Books
              Terzaghi and Peck - Soil Mechanics in Engineering Practice
              Cedergren, Harry., Seepage, Drainage, and Flow Nets
              Lamb and Whitman
Used Book Stores http://www.powells.com


NRCS Soil Mechanics Documents

Chapter 26, Part 633, NEH - Filter Design (Was Soil Mechanics Note 1)
SM Note 3 - Soil Mechanics Considerations for Embankment Drains
SM Note 4 - Preparation and Shipment of Undisturbed Core Soil Samples
SM Note 5 - Flow Net Construction and Use
SM Note 6 - Definitions and Terminology (obsolete - use ASTM D653)
SM Note 7 - The Mechanics of Seepage Analysis
SM Note 8 - Soil Mechanics Testing Standards - (Only use guide specs for geotechnical
       analyses - use ASTM or Corps of Engineers/Burec Standards for other tests
SM Note 9 -Permeability of Selected Clean Sands and Gravels
SM Note 10 - Supplement to the STABL2 Users Manual … - Obsolete
SM Note 11 - Static Cone Penetrometer (CPT) - Equipment and Using Data
SM Note 12 - Portable Pinhole Device
SM Note 13 - Dispersive Clays
Tr 26 and 27 - Compaction of Soils with Gravel
TR18 - Joint Gap Computations
TR60 - Chapters 5 and 6 - Stability Analysis and Seepage Control
Geology Note 5 - Sample Size Requirements
Appendix 10D to the Agricultural Waste Management Field Handbook - Geotechnical
       Design and Construction Guidelines
Construction Note 2 - field Density and Moisture Content Test - Nuclear Gauge Method
TR74 - Lateral Earth Pressures
TR78 - Characterization of Rock for Hydraulic Erodibility
NEH 19 - Construction Inspection



                                          1
NPEG – Geotechnical Engineering, Module 8, References


Corps of Engineer Documents

Downloadable from internet URL http://www.usace.army.mil/inet/usace-docs/
Examples
EM 1110-1-1801 - Geotechnical Investigations
EM 1110-1-1904 - Settlement Analysis
Em 1110-2-1901 - Seepage Analysis and Control for Dams, CH1
EM 1110-2-1913 - Design and Construction of Levees
EM 1110-2-1911 - Construction Control for Earth & Rock-Fill Dams
EM1110-2-2006 - Roller-Compacted Concrete
EM 1110-2-2300 - Earth & Rock-Fill Dams General Design and Construction
       Considerations
Also See Technical Manuals - for example,

Army TM 5-818-8, Engineering Use of Geotextiles, TM 5-818-1, Slope Stability
       Analysis
See Also Engineering Technical Letters

ETL 1110-2-544 Geotechnical Analysis By The Finite Element Method
ETL 1110-2-286 Publication Number: Engineering and Design - Use of Geotextiles
Under Riprap

Bureau of Reclamation Documents

Earth Manual, Part1 - Downloadable from internet URL
http://www.usbr.gov/tcg/earth/index.html
TADS (Training Aids for Dam Safety) Site http://www.usbr.gov/dsis/tads.html

Engineering Geology Field Manual Downloadable
Chapters 1-12 http://www.usbr.gov/geo/geolman

Ground Water Manual - order from the Superintendent of Documents -
Stock # 024-003-00179-1

Earth Manual - order from the Superintendent of Documents -
Part 1 Stock Number 024-003-00183-0 ($40)
Part 2 Stock number 024-003-00174-1 ($47)

Design of Small Dams order from the Superintendent of Documents
Stock Number 024-003-00164-3 Price $73

Engineering Geology Field Manual order from the Superintendent of Documents
Stock Number 024-003-00185-6 Price $36




                                          2
NPEG – Geotechnical Engineering, Module 8, References


Superintendent of Documents

http://bookstore.gpo.gov/index.html


National Technical Information Service (NTIS)

http://www.ntis.gov/
Caution - on First Screen - the Search button only gives results for publications since
1990. To get other search results, click on Place your order
On the resulting screen, be sure to search either before 1990 or after
Very helpful if you have NTIS number

Example - To find publication “Design and Construction of Compacted Shale
Embankments”, the NTIS number is PB 296506. By following directions on previous
screen, you find book with price of $54.50 (photocopy) and get order screen

If you don’t know order number for publications prior to 1990, you should call the sales
desk 1-800-553-6847 or email a request for the document to info@ntis.gov

Federal Highway Administration Geotechnical Engineering Publications

http://www.fhwa.dot.gov/bridge/geopub.htm


Navy Soil Mechanics Manuals

The US Navy Design Manuals are excellent references and are downloadable from the
internet. First go to the URL http://www.efdlant.navfac.navy.mil/lantops_15/
Click on publications.. Click on Design Manuals (DM). Find 7.01 - Soil Mechanics and
7.02 - Foundations and Earth Structures

Search Engines

Google.com is highly recommended
Enter as precise a search phrase as possible to limit number of returns.
Example - if you are looking for design guidance on geotextiles, first, examine results if
you only enter geotextiles - you get 18,500 results
Now, enter design guidance on geotextiles - you get 1,270 results
Then, enter filter design guidance geotextiles - and get only 375 results




                                             3
NPEG – Geotechnical Engineering, Module 8, References

Internet Bookmarks

Government Information Sources
http://www.usbr.gov/dsis/tads.html – Training Aids for Dam Safety – US Bureau of Reclamation

http://www.mvm.usace.army.mil/Readiness/97flood/flood.htm – Corps of Engineer site with pictures of
problems associated with 97 flood on Mississippi River and tribs

http://www.ntis.gov/ - National Technical Information Service – Source where you can order many
publications – fee

http://www.fhwa.dot.gov/bridge/geopub.htm – Federal Highway Administration Geotechnical Publications

http://www.usace.army.mil/inet/usace-docs/ - Home page for all Army Corps of Engineer Engineering
Publications – most engineering manuals are online and can be downloaded and printed by chapters

http://www.access.gpo.gov/su_docs/ - Government Printing Office

http://www.nalusda.gov/ National Agricultural Library

http://www.nationalacademies.org/trb/bookstore/ - Bookstore – source of many Highway Research
publications

http://www.wes.army.mil/REMR/remr.html – Repair, Evaluation, Maintenance and Rehabilitation
Research Program of the Corps of Engineers – source of good publications on rehab of old structures.

General Links for Geotechnical Topics
http://www.geoindex.com/geoindex – Geo-environmental search site

http://geotech.civen.okstate.edu/wwwvl/ - The virtual library of geotechnical engineering at Oklahoma
State

http://ceenve.calpoly.edu/fiegel/geolink.html – geotechnical links at Cal Poly

http://www.t-telford.co.uk/jolnew/welcome/ - Geotechnical journals from Britain online – subscription
required. Includes magazine Geotechnique

http://www.ggsd.com/ - Geotechnical and environmental software directory

Soil Testing Equipment
http://soiltest.com/ - ELE Soiltest testing equipment

http://www.hmc-hsi.com/ - Humboldt soil testing equipment

http://www.geo-solutions.com/Default3.htm – Information on slurry trench cutoff walls

Seismicity Information
http://geohazards.cr.usgs.gov/eq/ - National Seismic Hazards mapping project

http://www.eeri.org/ - Earthquake engineering research institute




                                                        4
NPEG – Geotechnical Engineering, Module 8, References

http://geohazards.cr.usgs.gov/eqint/html/lookup.shtml Probabilistic earthquake hazard lookup by latitude
and longitude – Some designers use horizontal acceleration with 2 % probability of exceedance in 50 years.
Compaction
http://www.ircmg.com/roadmachinery/compman/compman.html – Compaction primer from Ingersoll Rand

http://www.specialtysalesllc.com/nutra-bond_compaction.htm – Compaction information from Caterpillar

Landslides and Karst
http://cfd4.mit.edu/PGTdemo/karst/karcont.html – totor on karst (solutionized limestones)

http://www.consrv.ca.gov/dmg/pubs/notes/33/index.htm – mudslide hazards in California

http://landslides.usgs.gov/html_files/nlicsun.shtml – National Landslide Information Center (USGS)

http://www.maccaferri-usa.com/ - Gabions information

Saline and Alkaline Soils
http://www.ussl.ars.usda.gov/hb60/hb60.htm – downloadable version of Handbook 60 – out of print
publication on Diagnosis of Saline and Alkaline soils

Geosynthetic Products
http://www.ifai.com/ - International Fabrics Association

http://www.geosource.com/welcome.htm – geosynthetic links page

http://www.geosynthetica.net/ -    geosynthetics links page

http://www.geosynthetic-institute.org/publications.html – publications from Koerner’s geosynthetic
institute

http://www.linqind.com/techtoc.htm – Technical Notes on nonwoven geotextiles – including discussion of
permittivity

http://www.cetco.com/groups/lining/products/gcls.htm – Geosynthetic Clay Liners Information from
CETCO

Associations
http://www.aegweb.org/ - Association of Engineering Geologists

http://www.ngwa.org/ - National Groundwater Association

http://www.nas.edu/trb/ - National Transportation Research Board

http://www.damsafety.org/ - Association of State Dam Safety Officials




                                                     5
NPEG – Geotechnical Engineering, Module 9, Geotextiles

Objectives

1. Distinguish between major types of geosynthetic products
2. List the major functions of geotextiles
3. List the major types of geotextiles and advantages and disadvantages of each
4. Explain how to select a geotextile for a particular application using NRCS

Major Types of Geosynthetics

1. Geotextiles
2. Geomembranes, including GCL’s
3. Geogrids
4. Geocomposites
5. Geofoam
6. Geonets
7. Geocells guidelines

Technical specifications on a variety of synthetic products
      http://www.geosource.com/geosyn.htm

GFR - Geotechnical Fabrics Report - Annual Specifier’s Guide available from
International Fabrics Association International http://www.ifai.com - $47 annual

Engineering Use of Geotextiles - 58 page document
http://www.usace.army.mil/inet/usace-docs/armytm/tm5-818-8/entire.pdf


Geotextiles - includes woven and non-woven geotextiles for filtration, separation,
    drainage, stabilization and reinforcement functions.
Geogrids - includes extruded,woven, flexible and stiff types of geogrids for stabilization
    and reinforcement
Geomembranes - includes HDPE, PVC, CSPE, EPDM, and PP liners
      Geosynthetic Clay Liners - includes geotextile/clay/geotextile composites




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NPEG – Geotechnical Engineering, Module 9, Geotextiles

                                   CONSTRUCTION SPECIFICATION

                                            95. GEOTEXTILE

1. SCOPE
  This work shall consist of furnishing all materials, equipment, and labor necessary for the installation of
  geotextiles.

2. QUALITY
  Geotextiles shall conform to the requirements of Material Specification 592 and this specification.

3. STORAGE
  Prior to use, the geotextile shall be stored in a clean dry place, out of direct sunlight, not subject to
  extremes of either hot or cold, and with the manufacturer's protective cover in place. Receiving,
  storage, and handling at the job site shall be in accordance with the requirements in ASTM D 4873.

4. SURFACE PREPARATION
  The surface on which the geotextile is to be placed shall be graded to the neat lines and grades as shown
  on the drawings. The surface shall be reasonably smooth and free of loose rock and clods, holes,
  depressions, projections, muddy conditions and standing or flowing water (unless otherwise specified in
  Section 7).

5. PLACEMENT
  Prior to placement of the geotextile, the soil surface will be inspected for quality assurance of design
  and construction. The geotextile shall be placed on the approved prepared surface at the locations and
  in accordance with the details shown on the drawings and specified. The geotextile shall be unrolled
  along the placement area and loosely laid (not stretched) in such a manner that it will conform to the
  surface irregularities when material is placed on or against it. The geotextile may be folded and
  overlapped to permit proper placement in the designated area.

  Method 1 The geotextile shall be joined by machine sewing using thread of a material meeting the
  chemical requirements for the geotextile fibers or yarn. The sewn overlap shall be 6 inches and the
  sewing shall consist of two parallel stitched rows at a spacing of approximately 1 inch and shall not
  cross (except for any restitching). The stitching shall be a lock-type stitch. Each row of stitching shall
  be located a minimum of 2 inches from the geotextile edge. The seam type and sewing machine to be
  used shall produce a seam strength, in the specified geotextile that, as a minimum, is 90 percent of the
  tensile strength in the weakest principal direction of the geotextile being used, when tested in
  accordance with ASTM D 4884. The seams may be factory or field sewn.

  The geotextile shall be temporarily secured during placement of overlying materials to prevent slippage,
  folding, wrinkling, or other movement of the geotextile. Unless otherwise specified, methods of
  securing shall not cause punctures, tears or other openings to be formed in the geotextile.




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NPEG – Geotechnical Engineering, Module 9, Geotextiles

  Method 2 The geotextile shall be joined by overlapping a minimum of 18 inches (unless otherwise
  specified), and secured against the underlying foundation material. Securing pins, approved and
  provided by the geotextile manufacturer, shall be placed along the edge of the panel or roll material to
  adequately hold it in place during installation. Pins shall be steel or fiberglass formed as a "U", "L”, or
  "T" shape or contain "ears" to prevent total penetration. Steel washers shall be provided on all but the
  "U" shaped pins. The upstream or up-slope geotextile shall overlap the abutting down-slope geotextile.
  At vertical laps, securing pins shall be inserted through both layers along a line through approximately
  the midpoint of the overlap. At horizontal laps and across slope laps, securing pins shall be inserted
  through the bottom layer only. Securing pins shall be placed along a line approximately 2 inches in
  from the edge of the placed geotextile at intervals not to exceed 12 feet unless otherwise specified.
  Additional pins shall be installed as necessary and where appropriate, to prevent any undue slippage or
  movement of the geotextile. The use of securing pins will be held to the minimum necessary. Pins are
  to be left in place unless otherwise specified.

  Should the geotextile be torn or punctured, or the overlaps or sewn joint disturbed, as evidenced by
  visible geotextile damage, subgrade pumping, intrusion, or grade distortion, the backfill around the
  damaged or displaced area shall be removed and restored to the original approved condition. The repair
  shall consist of a patch of the same type of geotextile being used, overlaying the existing geotextile.
  When the geotextile seams are required to be sewed, the overlay patch shall extend a minimum of one
  foot beyond the edge of any damaged area and joined by sewing as required for the original geotextile
  except that the sewing shall be a minimum of 6 inches from the edge of the damaged geotextile.
  Geotextile panels joined by overlap shall have the patch extend a minimum of 2 feet from the edge of
  any damaged area.

  Geotextile shall be placed in accordance with the following applicable specification according to the use
  indicated in Section 7:

  a. Slope Protection The geotextile shall not be placed until it can be anchored and protected with the
     specified covering within 48 hours or protected from exposure to ultraviolet light. In no case shall
     material be dropped on uncovered geotextile from a height greater than 3 feet.

  b. Subsurface Drains The geotextile shall not be placed until drainfill or other material can be used to
     cover it within the same working day. Drainfill material shall be placed in a manner that prevents
     damage to the geotextile. In no case shall material be dropped on uncovered geotextile from a height
     greater than 5 feet.

  c. Road Stabilization The geotextile shall be unrolled in a direction parallel to the roadway centerline
     in a loose manner permitting it to conform to the surface irregularities when roadway fill material is
     placed on it. In no case shall material be dropped on uncovered geotextile from a height greater than
     5 feet. Unless otherwise specified, the minimum overlap of geotextile panels joined without sewing
     shall be 24 inches. The geotextile may be temporarily secured with pins recommended or provided
     by the manufacturer but they shall be removed prior to placement of the permanent covering
     material.




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NPEG – Geotechnical Engineering, Module 9, Geotextiles


6. MEASUREMENT AND PAYMENT
  Method 1 For items of work for which specific unit prices are established in the contract, the quantity
  of geotextile for each type placed within the specified limits will be determined to the nearest specified
  unit by measurements made of the covered surfaces only, disregarding that required for anchorage,
  seams, and overlaps. Payment will be made at the contract unit price. Such payment will constitute full
  compensation for the completion of the work.

  Method 2 For items of work for which specific unit prices are established in the contract, the quantity
  of geotextile for each type placed within the specified limits will be determined to the nearest specified
  unit by computing the area of the actual roll size, or partial roll size installed. The computed area will
  include the amount required for overlaps, seams, and anchorage as specified. Payment will be made at
  the contract unit price. Such payment will constitute full compensation for the completion of the work.

  Method 3 For items of work for which specific lump sum prices are established in the contract, the
  quantity of geotextile will not be measured for payment. Payment for geotextiles will be made at the
  contract lump sum price and will constitute full compensation for the completion of the work.

  All Methods The following provisions apply to all methods of measurement and payment.
  Compensation for any item of work described in the contract but not listed in the bid schedule will be
  included in the payment for the item of work to which it is made subsidiary. Such items and the items
  to which they are made subsidiary are identified in Section 7 of this specification.




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NPEG – Geotechnical Engineering, Module 9, Geotextiles


Insert page 2 of geotextile material specification




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NPEG – Geotechnical Engineering, Module 9, Geotextiles


Insert page 3 of geotextile material specification




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NPEG – Geotechnical Engineering, Module 9, Geotextiles


Insert page 4 of geotextile material specification




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NPEG – Geotechnical Engineering, Module 9, Geotextiles


Insert page 1 through 10 of the geotextile manual




                                        8
NPEG – Geotechnical Engineering, Module 10, Parametric Analyses



Parametric Analyses


Objectives

   1. Explain reasons parametric analyses are used
   2. Explain use of parametric analyses in slope stability, settlement, and seepage
      studies
   3. Define Safety factor and explain its primary value in Geotechnical Engineering

Reasons for Parametric Analyses

Variability of Natural Soils
Limitations of laboratory scale samples to duplicate field scale deposits
Shear tests on 1.4”diameter specimens
Consolidation tests on 3/4”to 1”thick specimens
Permeability tests on 3”diameter by 3”high specimens

Basis of Parametric Analyses

In a parametric analyses, the value of one parameter is varied to examine the result on the
calculation. Examples follow for Slope Stability, Settlement, and Seepage

Parametric Analysis for Slope Stability

Examine how the predicted safety factor varies for assumed values of foundation shear
strength

Parametric Analysis for Settlement

Examine how the settlement varies for assumed values of foundation preconsolidation

Parametric Analysis for Seepage

Examine how the seepage quantity varies for assumed values of foundation permeability

Parametric Analysis for Seepage

Examine how the location of the phreatic surface varies for assumed values of
stratification of permeability




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NPEG – Geotechnical Engineering, Module 10, Parametric Analyses



Safety Factors in Geotechnical Engineering

After Sherard (One of the most widely respected embankment design engineers)

       The primary value in safety factors is not as an absolute indicator of the safety
       of a particular design, but in comparing the relative safety of several alternative
       designs. This allows a more rational evaluation of design alternatives.

Safety Factors in Geotechnical Engineering

Examples. Compare the safety factor of an embankment with no berm to that for an
embankment with a 40’berm at about 1/4th the dam’s height. Compare the cost of the
embankment with and without the berm and consider the increased safety factor with the
berm in deciding on whether the berm is worthwhile

Added Example of Parametric Analysis for Seepage

Compare the quantity of seepage for varying depths of a cutoff trench

Criterion

Parametric analyses don’t eliminate the need for certain minimum design standards.
These are based on valuable empirical history and should be followed. TR60, others

Example - Seepage computations often consider a safety factor of 10 to allow for poor
      estimates of permeability.

Slope stability safety factors are generally from 1.3 to 1.5 based on few failures occurring
       where designs obtained these values




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