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PILE FOUNDation by hcj

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									    PILE
FOUNDATIONS
          By
     Rajesh Kumar
   Professor Track 1




         1
1.0       Historical background

      Driving of bearing piles to support structures is one of the earliest
examples of the art and science of the civil engineer. Timber pillars were
used as early as in 200BC to 200AD. Timber because of its strength
combined with lightness, durability and ease of cutting and handling,
remained the only material used for piling until comparatively recent times.

        It was replaced by concrete and steel only because these newer
materials could be fabricated into units that were capable of sustaining
compressive, bending and tensile forces for beyond the capacity of a timber
pile of like dimensions. Reinforced concrete, which was developed as a
structural medium in the late nineteenth and early twentieth centuries, largely
replaced timber for high capacity piling for works on land. The partial
replacement of driven precast concrete piles by numerous forms of cast-in-
situ piles has been due more to the development of highly efficient machines
for drilling pile bore holes of large diameter and great depth in a wide ranged
soil and rock conditions, than to any deficiency in the performance of the
precast concrete element. Steel has been used to an increasing extent for
piling due to its ease of fabrication and handling and its ability to withstand
hard driving problem of corrosion in marine structures have been overcome
by the introduction of durable coatings and cathodic protection.

2.0    Establishment of need for a pile

Need of a pile foundation can be justified in the following situations:-

(a)   Upper soil strata are too compressible or generally too weak to support
heavy vertical reaction transmitted by the super structure.

      In this instance piles serve as extensions of columns or piers to carry
       the loads to a deep, rigid stratum such as rock (Point bearings piles).

      If such a rigid stratum does not exist with in a reasonable depth, the
       load must be gradually transferred, mainly by friction, along the pile
       shafts (friction piles)




             Fig.1: Point Bearing Files              Fig.2: Friction Piles

                                        2
(b)    Piles are also frequently required because of the relative inability of
shallow footings to transmit inclined, horizontal, or uplift forces and
overturning moments. Such situations are common in design of earth
retaining structures (walls and bulk heads) and tall structures subjected to
high wind and earthquake forces.

     Piles resist upward forces by negative friction around their shafts (up
      lift piles).




                           Fig.3: Uplift Piles

(c)   Horizontal forces are resisted either by vertical piles in bending or
      by groups of vertical and battered piles (Fig. 4 & 5).




           Fig.4                                    Fig.5




                                       3
(d)   Pile foundations are often required when scour around footings could
cause erosion inspite of the presence of strong, incompressible strata (such
as sand or gravel) at shallow depths (Fig&6).




                        Fig.6

(e)    In areas where expansive or collapsible soils extend to considerable
depth below the soil surface, pile foundations may be needed to assure
safety against undesirable seasonal movements of the foundations (fig.7).




                           Fig.7




                                     4
3.0    Classification of piles:
       Piles can be classified in the following ways:-

3.1    On the basis of Material:
           Timber
           Steel
           PCC
           RCC
           PSC
           Composite

3.2    On the basis of Method of Construction:-
           Driven/displacement precast piles
           Driven/displacement cast in situ piles
           Bored/replacement precast piles
           Bored /replacement cast in situ piles

 3.3    On the Basis of Sectional Area:-
            Circular
            Square
            Tubular
            Octagonal
            H-section

3.4    On the Basis of Mode of Load Transfer:-

            End bearing piles
            Friction piles
            Bearing cum friction piles

3.5    On the Basis of Size of Piles:-
           Micro (Mini) Piles    (<150 mm)
           Small diameter piles    (>150 mm < 600mm)
           Large diameter pile      (>600 mm)




                                      5
3.6   On the Basis of Inclination of Piles:-

           Vertical piles
           Raker (batter piles)




                            End Bearing Pile




                                   Friction Piles




                                     6
   Driven Piles




   Bored Piling




Driven Cast in Situ




    7
4.0     Choice Of Pile Material:

        Principal advantages and disadvantages of different pile materials.

Material            Advantages                         Disadvantages
Timber              Easy to handle or cut off,         Decay above water table,
                    relatively inexpensive material.   especially in marine
                    Readily available, naturally       environment, Limited in size
                    tapered, Light and very durable    and bearing capacity, Prone to
                    below ground level.                damage by hard driving, Noisy
                                                       to drive.
Steel               Easy to handle, cut off, extend.   Subject to corrosion, require
                    Available in any length or size,   protection in marine
                    can penetrate hard strata,         environment. Flexible H-piles
                    boulders, soft rock. Convenient    may deviate from axis of
                    to combine with steel              driving. Relatively expensive
                    superstructure, ability to         material than timber and
                    withstand hard driving, capable    concrete. Noisy to drive.
                    for heavy loads.
Concrete:           Durability in almost any           Cumbersome to handle and
Precast             environment. Convenient to         drive. Cumbersome to handle
                    combine with concrete              and drive. Difficult to cut off or
                    superstructure.                    extend. Noisy to drive

Cast-in-situ:       Allows inspection before           Casting cannot be re-used. Thin
Casting left in     concreting. Easy to cut off or     casing may be damaged by
ground              extend.                            impact or soil pressure.
Casting with-       No store space required. Can       In soft soils shaft may be
drawing or no       be made before excavation.         squeezed by soil cave in. In
casting.            Some types allow larger            case of heavy compaction of
                    displacement in weaker soils.      concrete previously completed
                    Some types have no driving         piles may be damaged. If
                    operation, suitable where noise    concrete is placed too fast there
                    and vibration are prohibited       is danger of creation of a void.
                    (down town).

5.0     Factors Governing Choice Of Type Of Pile:

5.1 The type of Pile shall be selected by considering broadly the
following factors:-

        1.        Availability of space
        2.        Proximity to structures
        3.        Reliability

      The advantages and disadvantages of the various forms of pile affect
the choice of pile for any particular foundation project and these are
summarized as follows:-




                                            8
5.2   Driven Pre cast Piles -

            Advantages:
      •     Material forming pile can be inspected for quality and soundness
            before driving
      •     Not liable to „squeezing‟ or „necking‟
      •     Construction operations not affected by ground water
      •     Projection above ground level advantageous to marine
            structures
      •     Can be driven in very long lengths
      •     Can be designed to withstand high bending and tensile stresses

            Disadvantages:
      •     Unjointed types cannot readily be varied in length to suit varying
            level of bearing stratum
      •     May break during driving necessitating replacement piles
      •     May suffer unseen damage which reduces carrying capacity
      •     Uneconomical if cross-section is governed by stresses due to
            handling and driving rather than by compressive, tensile, or
            bending stresses caused by working conditions
           Noise and vibration due to driving may be unacceptable
           Displacement of soil during driving may lift adjacent piles or
            damage adjacent structures
           End enlargements, if provided, destroy or reduce skin friction
            over shaft length
           Cannot be driven in conditions of low headroom

5.3   Driven-and-cast-in-situ piles -

      Advantages
      •    Length can easily be adjusted to suit varying level of bearing
           stratum
      •    Driving tube driven with closed end to exclude ground water
      •    Enlarged base possible
      •    Formation of enlarged base does not destroy or reduce shaft
           skin friction
      •    Material in pile not governed by handling or driving stresses
      •    Noise and vibration can be reduced in some types by driving
           with internal drop-hammer




                                     9
      Disadvantages
      •     Concrete in shaft liable to be defective in soft squeezing soils or
            in conditions of artesian water flow where withdraw able-tube
            types are used
      •     Concrete cannot be inspected after installation
      •     Length of some types limited by capacity of piling rig to pull out
            driving tube
      •     Displacement may damage fresh concrete in adjacent piles, or
            lift these piles, or damage adjacent structure
            Noise and vibration due to driving may be unacceptable
            Cannot be used in river or marine structures without special
             adaptation
            Cannot be driven with very large diameters
            End enlargements are of limited size in dense or very stiff soils
            When light steel sleeves are used in conjunction with
             withdrawalable driving tube, skin friction on shaft will be
             destroyed or reduced.

5.4   Bored and cast – cast in situ replacement Piles:-

      Advantages
          Length can readily be varied to suit variation in level of bearing
           stratum
          Soil or rock removed during boring can be inspected for
           comparison with site investigation data
          In-situ loading tests can be made in large diameter pile bore
           holes, or penetration tests made in small boreholes
          Very large (up to 7.3m diameter) bases can be formed in
           favourable ground
          Drilling tools can break up boulders or other obstructions which
           cannot be penetrated by any form of displacement pile
          Material forming pile is not governed by handling or driving
           stresses
          Can be installed in a very long lengths
          Can be installed without appreciable noise or vibration
          No ground heave
          Can be installed in conditions of low headroom

            Disadvantages
      •     Concrete in shaft liable to squeezing or necking in soft soils
            where conventional types are used.
      •     Special techniques needed for concreting in water-bearing soils
      •     Concrete cannot be inspected after installation
      •     Enlarged base cannot be formed in cohesionless soils
      •     Cannot be extended above ground level without special
            adaptation


                                      10
        •      Low end-bearing resistance in cohesionless soils due to
               loosening by conventional drilling operations
        •      Drilling a number of piles in group can cause loss of ground and
               settlement of adjacent structures

6.0    Piling equipment and methods:

       Equipments for Installing precast driven piles
       Equipments for installing driven and cast in situ piles
       Equipments for installing bored and cast in situ piles

6.1.   Equipment for installing pre cast driven piles:

       (i)     Pilling frames:- has the function of guiding the piles at its
               correct alignment from the stage of first pitching in position to
               its final penetrations.      It also carried the hammer and
               maintaining it in position co-axially with the pile.
       (ii)    Crane Supported (hanging) Leaders
       (iii)   Trestle guides
       (iv)    Piling hammers:- Selection depends on type and weight of the
               pile, characteristic of ground, volumed energy per blow, the
               striking rate and the fuel consumption. Single and double acting
               hammer are effective in all type of soils.




                         Principle of operation of pile drivers




                                       11
6.2 Equipment for installing driven and cast in situ piles:           Same
equipments which are used for Driven Piles are generally used for installing
Driven and Cast in situ Piles


6.3   Equipment for installing Bored and cast in situ piles:

      (i)    Power augers:- Power driven rotary auger drilled are suitable
             for installing bored piles in clay soils. The “highway” spiral plate
             auger is a lorry mounted machine which can drill holes up to
             1370mm in diameter and to depths up to 12.5m.




                                               ‘Highway’ Lorry-mounted
                                               auger drill




      The range of “Terra Drill” machines manufactured for attachment to
standard crawler cranes, is from 254mm diameter bore hole to a depth of
26m for the smallest size to 3.5m dia meter bore holes to depth of up to
100m. This machine is manufactured by BSP interaction foundations limited




                                      12
Tera Drill
Model




(ii)   Various types of equipments are available for use with rotary
       augers.    The standard and rock augers have scop-bladed
       openings fitted with projecting teeth.




                              Coring Bucket




                              13
           The coring bucket is used to raise a solid core of rock




 Bentonite Bucket is designed to avoid scouring the mud cake, which
 forms, on the wall of the bore holes.




                                Bentonite Bucket


       Enlarged or under reamed bases can be cut by rotating a belling
bucket within the previously drilled straight sided shaft. The bottom hinged
bucket cuts to a hemispherical shape and because it is always cutting at the
base it produced a clean and stable bottom. However the shape is not so
stable as the conical form produced by the top hinged bucket have a
tendency to jam when raising the bucket. But this type requires a separate
cleaning operation of the base after under reaming. Belling buckets normally
form enlargements up to 3.7m in dia but can excavate to a diameter of 6.1m
with special arrangements. Belling bucket requires a shaft diameter of at
least 0.76m. The essential condition for the successful operation of a rotary
auger rig is a cohesive soil which will stand without support or a cohesionless
soil supported by bentomite slurry. In these conditions fast drilling rates of
up to 7M per hour are possible for smaller shaft size.




                                      14
Rotary Bored Piling




Rotary Bored Piling




 Rotary Bored Piling




      15
 Under Reaming Rig




Under Reaming Rig




     16
(iii)   Grabbing Rigs with Casing Oscillators:-             Suitable for
        drilling through sands, gravels and loose rock formations, the
        pile bore holes may required continuous support by means of
        casing. It imparts a semi rotating motion to the casing through
        clamps.




                         Continuous Flight Augur



(iv)    Reverse circulation drilling rigs:-            Operates on the
        principle of the air lift pump. Compressed air is injected near
        the base of the centrally placed discharge pipe. The rising
        column of air and water lifts the soil which has been loosened
        by rotating cuffers and the casting tubes are also rotated to
        keep them freely moving in the soil as they sink down while the
        boring advances. It can drill at a fast rate in a wide range of
        ground conditions including weak rocks. Most effective in
        granular soil.

(v)     Tripod rigs: Small diameter piles with diameter up to 600mm
        installed in soils which requires continuous support by lining
        tubes are drilled by tripod rigs. Suitable if head room is
        restricted for deployment of other auger




                                17
(vi)     Drilling of piles with Bentomite slurry: Lining tubes or
        casings to support the sides of pile bore holes are a requirement
        for most of the bored pile installation methods. Even in stiff
        cohesive soils it is desirable to use casings for support since
        these soils are frequently fissured.

       Casings can be avoided completely (except for a short length
        used at the top hole) by proving support to the pile bore hole in
        the form of a summer of bentomite clay.

       It is used most efficiently in conjunction with reverse circulation
        rigs.

       The slurry is pumped into the outer casing and the slurry soil
        mixture that is discharged from the air lift rise pipe is allowed to
        settle in lagoons to remove soil particles.

(vii) Basic properties of drilling mud (bentonite): Clay of
      montmorillonite group. having exchangable sodium cations. on
      dispersion break down into small plate like particles having a
      negative charge on the surfaces and positive charge on the
      edges. When dispersion is left to stand undisturbed , the particle
      becomes oriented building up a mechanical structure at its own.
      This mechanical structure held by electrical bonds behave like
      jelly material. When the jelly is agitated, the weak electrical
      bonds are broken and the dispersion becomes FLUID.

   LL > 300 % < 450 % ( tested as per IS 2720 (PART V) –1965 )
•   Sand content> 7 %
•   Density of freshly prepared/bentonite suspension 1.034 to 1.10
    kg./lit.
•   Density after contamination upto 1.25 kg. / lit.
•   The marsh viscosity ( tested by a marsh cone ) between 30 to 60
    seconds
•   The marsh viscosity may be upto 90 seconds in special cases but in
    these cases special type of pumping equipments will have to be
    used.
•   The differential free swell > 540 %
•   pH value from 9 TO 11.5




                                 18
7.0    Design and Analysis of Pile Foundations.

      Design and analysis is done based on the following:
•     Code of practice for the design of sub-structures and foundations of
      Bridges issued by Railway Board.
•     Manual on the Design and Construction of well and pile Foundations
      issued by RDSO.

        Design shall be considered in relation to the nature of ground, manner
in which load transfer take place, behavior of group piles and settlement.

7.1    Spacing of Piles:

        Normally centre to centre spacing shall not be more than 4d, where d
is the diameter of the piles. In case of non circular section „d‟ will be the
diameter of the circumscribing circle. Friction pills shall be sufficiently for
apart to ensure that the zones of influence surrounding them do not over lap
to such an extent that their carrying capacities are appreciably reduced.
Generally the spacing shall not be less than 3d. For end bearing piles passing
through relatively compressible strata, the spacing shall not be less than 2.5d
to avoid heaving of soil.

7.2    Load carrying capacity:

The ultimate bearing capacity of a pile may be assessed by means of –

      (a)    Dynamic pile formula, or
      (b)    Using data obtained during driving of piles, or
      (c)    By static formula on the basis of soil test or
      (d)    By a load test.

        For non-cohesive soils, Hiley‟s formula is more reliable than others
(IS:2911 (Part-I) 1969. Hiley‟s formula is not reliable for cohesive soils. The
static formula should be used with careful judgment, as the mechanics of load
transfer from pile to soil is complex. In unknown areas, load test is therefore
more desirable. Where scour is anticipated, resistance due to skin friction will
be available only below the scour line. When piles are installed through
compressible fill or sensitive clay in to under laying hard stratum, a drag down
force is generated in the fill or the clay stratum. This must be added to the
load.




                                      19
7.3          Factor of safety for Pile Foundation:

Factor of safety shall be judiciously chosen after considering the following:

       (a)    Reliability of the soil parameters.
       (b)    Type of superstructure and nature of loading.
       (c)    Possible reduction in the strength of the sub-soil strata arising
              out of the installation technique.
       (d)    Experience of similar structure near the site.

        The minimum factor of safety of static formula shall be 3. The final
selection of the factor of safety shall take in to consideration the total
settlement and differential settlement of the structure. The ultimate safe load
capacity shall be obtained wherever practical from a load test (I.S.
Code:2911=Part-I-1964). A minimum factor of safety shall be 2, on the
ultimate load capacity, if obtained from load test.

7.4    The factor of safety based on load Test shall be increased in
following unfavorable conditions:-

       (a)     Settlement is to be limited or unequal settlement avoided
       (b)     Large impact or vibrating loads are expected
       (c)    The properties of the soil are expected to deteriorate with time
       (d)    The live load on a structure carried by friction piles is a
              considerable portion of the total load.

    The maximum permissible increase over the safe load of a pile on
account of wind load is 25%

7.5    Over Loading of Piles:

        An over loading up to 10% of the pile capacity may be allowed on each
pile. For a group of piles, the maximum over loading on the group shall be
restricted to 40% of the allowable load on a single pile of the group. This over
loading shall not be allowed at the initial design stage.

The bearing capacity of a pile group may be worked out as under:

        Strata                          Type of     Bearing capacity of the Pile
                                        Pile        group
        1) Dense sand not underlain     Driven      No. of piles x SPC*
        by weak deposit
        2) Loose sandy soil                         ½ (Nos. of piles x SPC*)
                                                    2
        3) Sand not underlain by        Bored        /3 (No. of piles x SPC*)
        weak deposit

       SPC = Single Pile Capacity



                                       20
8.0   Construction Aspects of Bored Cast in Situ Piles:

•     IS CODE : 2911 PART I SEC.2
•     Generally used for pile dia up to 2500 mm.
•     In soft clays and loose sands, bailer and chisel method is used.
•     Rotary or percussion type drilling rigs using DMC or RMC method

8.1 The size of the cutting tool should not be less than the dia. Of the pile
by more than 75 mm. Use of drilling mud for stabilising the sides of the bore
hole is also made. Permanent MS liner may be used on top 2-3m to prevent
the bore collapse.

8.2 Reinforcement: minimum area of long reinforcement = 0.4% of the
sectional area (calculated on the basis of outside area of the casing or the
shaft). The minimum clear cover = 40mm. The minimum clear distance
between main reinforcement = 100mm. The minimum dia of the links =
6mm. Minimum clear distance between links = 150mm.

8.3 Pile Cap: The clear overhang of pile cap beyond the outermost pile in
the group = 100mm to 150mm. The pile should project 50mm into the cap
concrete. The minimum clear cover for the main rein in the cap 60mm. The
cap is generally cast over a 75 mm thick levelling course.

       For piles of smaller dia and depth up to 6 met. – minimum quantity of
cement 350 kg./m3. For piles of bigger dia and depth more than 6 met. –
minimum quantity of cement 400 kg./m3 and grade M-20. 10 % extra cement
to be used for under water concreting. Slump of concrete 150 to 180 mm.

8.4 Alignment control - for vertical piles a deviation of not more than
1.5 %. For raker piles a deviation of not more than 4%. Pile should not
deviate more than 75 mm or D/4 whichever is less ( for piles less than or
equal to 600 mm dia.). 75 mm or D/10 whichever is more for more than 600
mm. Dia. Pile.

       In case of single pile in column position, 50mm or D/4 whichever is
less for piles up to 600mm dia. 100mm for piles more than 600mm dia.
Manual chipping of top of the pile may be permitted – after 3 days of pile
casting. Pneumatic chipping after 7 days of pile casting.




                                     21
8.5   Tremie Concreting:




       Concrete should be rich in cement (not less than 370 Kg/m3). Slump
= 150mm to 180mm. In under water – casting for full depth or 2 M if non
collapsible stratum. If under drilling mud – no casing is required except near
the top.

       No leakage at the joints. The tremie pipe should be of min. 200 mm
dia. The first charge of the concrete should be placed with a sliding plug
pushed down the tube ahead of it. The plug should be taken out and not to
be buried into concrete. The tremie pipe should always penetrate well into
concrete with an adequate margin. All tremie pipes should be cleaned
thoroughly after concreting. The concreting of piles should be uninterrupted.
The interruption should not be more than 1 to 2 hours.

The top of the concrete in a pile shall be brought above the cut off level to
permit removal of all laitance and weak concrete. Tremie concreting should
be up to piling platform level or to a min. of one meter above the cut off
level.

      In other cases - Min. 0.3 met. above the cutoff level , if cutoff level is
less than 1.5 met. below the working platform level. For each additional 0.3
met. increase in cut-off level below the working level, the additional coverage
of 50 mm.




                                      22
                            Tremie Concreting

8.6   Rock socketing: For the end bearing piles.

Sound, relatively homogenous rock including granite and gneiss - 1 to 2d.

Moderately weathered closely formed including schist & slate - 2 to 3d.

For Soft rock- 3 to 4d

8.7   Problems in bored cast in situ pile construction
•     Overbreak
•     Base of bore hole
•     Extracting temporary casing
•     Soft ground
•     Drilling mud
                              Necking in Pile




                                      23
Necking in Pile




Necking in Pile




Necking in Pile




Necking in Pile




      24
Necking in Pile




           Necking Pile


   Necking in Pile




      25
8.8        Flow Chart for Pile Selection:-




9.0         Site Investigations:

        As and when a site investigations is planned it is not always certain that
piled foundation will be necessary. Therefore the program for the site work
should follow the usual pattern for a foundation investigation with bore holes
that are sufficient in number to give proper coverage of the site both laterally
and in depth. If it become evident from the initial boreholes that piling is
required, or is an economical alternative to the use of shallow spread
foundations, then special attention should be given to ascertaining the level,
and characteristics of a suitable stratum in which the piles can take their
bearing the bores should be drilled to a depth of 1.5 times the width of the
pile group or 10 mtrs which ever is less below the intended base level of the
pile, or 1.5 times the width of the equivalent raft below the base of the raft.




                                        26
        If the piles can be founded on a strong and relatively incompressible
rock formation then drilling need not be taken deeper than a few meters
below rock head to check that there are no layers or lances of weak
weathered rock which might impair the base resistance of individual piles.
However there must be reliable geological evidence that the bearing stratum
is not under lair by weak compressible rocks or the large boulders is not
mistaken for rocks. Cased shell and auger borings followed by rotary case
drilling to prove the rock conditions can be costly when drilled in large
numbers at the close spacing required to establish a detailed profile.
Geophysical exploration by seismic refraction on land and by continuous
seismic profiling at sea are economical methods for over large areas.
Geophysical methods are not usually economical for small site areas. Trial
pits are often a useful adjunct to bore hole exploration for a piling project.
Cable percussion borings give the most reliable information for piling work.
Cable percussion or flight auger drilling cannot penetrate large and hard
boulders, and it is the usual practical to bring a rotary drill over the hole to
core through the boulders, so obtaining information on its size and hardness.
Rock drilling is desirable to be done by rotary case drilling. The most useful
in situ test for piling investigation is the standard penetration test.




                 Required depth of boreholes for pile groups
                 in compressible soils




                                      27
10.0   Pile Load Test (IS-2911 Prt-IV):

10.1   Stress Testing:
      Maintained load test.
      Constant Rate of penetration test.
      Dynamic load test.
      Horizontal load Test.
      Cyclic Load Test

10.2 Strain Testing:
    Low Strain Integrity Testing
    High Strain Integrity Testing


                                Static Load Test




                                      28
Pile Load Test (Kenteledge Arrangement)




     Pile Load Test (With Anchor Piles)




               29
10.3 Initial Test: To determine ultimate load capacity and safe load
capacity. To study the effect of piling on existing structures. To decide the
suitability of piling system. To have a check on calculated load by dynamic or
static approaches.

       The safe load on a single pile will be least of the following:

       a)    Two third of the final load at which total displacement attains a
              value of 12mm.
       b)    50% of the final load at which the total displacement equals 10%
             of the dia of pile.

       The safe load for group of piles:

       a)     Final load at which total displacement is 25 mm.
       b)     Two third of final load at which displacement is 40 mm.

10.4 Routine Test:
     Test load will be at least 1.5 times the working load.
      Max. Settlement > 12 mm.
      For group of piles max. Settlement > 25 mm.

10.5   Initial and routine test: Settlement should be recorded by min. 2
       dial gauges for single pile (0.01 mm sensitivity). Gauges should be
       positioned on datum bars resting on immovable supports at a distance
       of 3d (Subject to min 1.5 m.) from the edge of pile.


                               Load Settlement Curve




                                        30
10.6   Maintained load test:

      Applicable both for initial and routine test -
      Load is applied in increments
      Displacement is measured
      Next increment will be applied when the rate of settlement is less than
       0.1 mm in 30 min. Or 0.2 mm in 1 hour or till 2 hours whichever occur
       first.
      The test load shall be maintained for 24 hours.

       Load is increased in stages to some multiple, say 1.5 times or twice the
working load with the time settlement curve recorded at each stage of loading
and unloading. The maintained load test is best suited for contract works
particularly for proof loading test on working piles.

       CRP & ML test use the same type of loading arrangements and pile
preparation.


10.7   Constant Rate of Penetration Test:-

       Compressive force is progressively increased to cause the pile to
penetrate the soil at a constant rate until failure occurs. CRP is essentially a
test to determine the ultimate load on a pile and is therefore applied only to
preliminary test piles or research type investigation. The method has the
advantage of speed in execution and because there is no time for
consolidation or creep settlement of the ground, the load settlement curve is
easy to interprete. BS-8004 states that penetration rates of 0.75mm/min are
suitable for friction piles in clay and 1.55mm/min for piles end bearing in a
granular soil.

        The CRP test is not suitable for checking the compliance with
specification requirements for the maximum settlement at given stage of
loading. There is also difficulty of pricing tenders for this form of load testing
since the failure lead on the pile is not known with any certainty until the test
is made.

       More suitable for determining ultimate load bearing capacity in
comparison to maintained load test. Used for initial test only. Two dial
gauges of 0.01mm accuracy are used. Readings of time, penetration and
load should be taken at close intervals to give adequate control of the rate of
penetration. A rate of penetration of 0.75 mm per min. is suitable for
predominantly friction piles. A rate of penetration of 1.5 mm per min. is
suitable for predominantly end bearing piles. A curve between load and
penetration should be drawn to determine ultimate load bearing capacity.




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32
11.0 Durability and protection of timber piles:

11.1 Timber piles permanently below ground water level have an indefinite
life. There are numerous examples of timber piles that are more than 2000
yrs old being found in excavations below the water level. While timber does
not decay from fungal attack if the moisture content is kept below 20%. It is
impossible to maintain it in this dry condition when buried in the ground
above water level. Precaution against fungal attack must be commenced at
the time the timber is felled by properly stacking at proper place. Suitable
methods of preserving timber for piling work involve pressure impregnation
with creosote or a solution of copper sulphate and potassium dichromate
(celcure). The adoption of preservations treatment does not give indefinite
life above ground level, it may be preferable to adopt a composite pile having
a concrete upper section. For timber piles in river and marine structure, the
most destructive agency which can occur in piles immersed in brackish or
saline water is attack by Molluscan or crustacean bores. It may result into
complete destruction of the piles.

      Following methods of protecting timber piles against attack by bores
may be adopted.

        Tipping stone around the piles (this protect only the length covered by
the stores). Sleeving the timber with galvanized iron, copper of aluminum
sheeting. Encasing the piles, jacketing the piles with pre cast concrete tubes
and filling the space between the timber and the tubes with cement grout.
Coating the piles with cement sand mortar, applied with a spray gun (eg. the
„Shotcrete‟ or „Gunite‟ process).

11.2     Durability and protection of Concrete piles.

        Properly mixed concrete compacted to a dence impermeable mass is
one of the most permanent of all constructional material and give little cause
of concern about its long-term durability in a non aggressive environment.
However concrete can be attacked by sulphate and sulfuric acid occurring
naturally in soils, by corrosive chemicals which may be present in industrial
waste in fill materials and by organic acids and carbon dioxide present in
ground water as a result of decaying vegetable matters. Attack by sulphates
is a disruptive process whereas the action of organic acids or dissolved carbon
dioxide is one of leaching. Attack by sulphuric acid combines features of both
process. The severity of attack by soluble sulphates must be assessed by
determining the soluble sulphate content and the proportions of the various
cataions present in an aqueous extract of the soil. These determinations
must be made in all cases where the concentration of sulphate in a soil
sample exceeds 0.5%.




                                      33
        A dense, well compacted concrete provides the best protection against
the attack by sulphater on concrete piles, pile cap and ground beams. The
low permeability of dense concrete prevents or greatly restricts the entry of
the sulphates in to the pore spaces of the concrete. For this reason high
strength pre cast concrete piles are most favorable type to use. However
they are not suitable for all the site conditions and bored cast in situ / driven
cast in situ piles if adopted must be designed to achieve the required degree
of impermeability and resistance to aggressive action. Neither high alumina
cement nor super sulphated cement is favoured for piling work. Instead,
reliance is placed on the resistance of dense impermeable concrete made with
a low water cement ratio. Coating of tar or bitumen on the surface, metal
sheating or glass fibre wrapping impregnated with bitumen may be adopted.

       Pile caps and ground beams can be protected on the underside by a
layer of heavy gauge polythene sheeting laid on a sand carpet or on blinding
concrete. The vertical sides can be protected after removing the form work
by applying hot bitumen spray coats, bituminous paint, trowelled on mastic
asphalt or adhesive plastic sheeting.

       Precautions against the aggressive action by sea water on concrete
need only be considered in respect of precast concrete piles. Cast in situ
concrete is used only as a hearting to steel tubes or cylindrical precast
concrete shell pills. For precast concrete piles for marine condition, a
minimum ordinary port land cement content of 360 kg/m3 and a maximum
water cement ratio of 0.45 by weight should be adopted.

11.3       Durability and protection of Steel piles:

        Corrosion of iron or steel in the electrolyte provided by water or moist
soil is an electro-chemical phenomenon in which some areas of the metal
surface act as anodes and other areas act as cathods. Pitting occurs in
anodic areas, with rust as the corrosion product in cathodic areas. Air and
water are normally essential to sustain corrosion but bacterial corrosion can
take place in the absence of oxygen i.e. in anaerobic conditions. Anoerobic
corrosion is caused by the action of sulphate – reducing bacteria which thrive
below the sea or river bed in polluted waters, particularly in relatively
impermeable silts and clays. Where steel piles are buried in fill or disturbed
natural soil, the thickness of metal in a bearing pile should be such that the
steel section should not over stressed due to wastage of the metal by
corrosion over the period of the useful life of the structure. Maximum rates of
corrosion may be taken as 0.08mm / year.

       In contaminated ground where corrosion of steel may be higher than
normal, some protection over the length of pile above and a depth of 0.6m
below the water table can be given by two coats of coal-tar-pitch paint
applied cold to a metal surface.




                                       34
       Other protective measures in contaminated disturbed ground includes
jacketting the pile with concrete or filling the shafts of hollow piles with
concrete capable of carrying the full load, where water table is shallow the
pile can be extended down to a depth of 0.6m below water level to protect
the steel of the pills. .

11.4 Steel piles for marine structures:

      Steel piles supporting jetties, offshore platforms, and other river or
marine structures must be considered for protection against corrosion in five
separate zones. These are as follows:

Zone                                     Recommended protection
Atmospheric Zone:                        Coal tar epoxide paint to 250mm film
Exposed to the damp conditions of        thickness to give estimated 10 year
the atmosphere above highest water       life.
level or to airborne spray.
Splash Zone: above mean high water                        -do-
level and exposed to waves and spray
and wash from ships.
Intertidal Zone:                         Bare steel to nominal or increased
Between mean high water level and        thickness to allow for corrosion loss
exposed to waves an spray and wash       (because of uncertainty in driving
from ships.                              depths, it may be necessary to
                                         extend the paint treatment from the
                                         splash zone into the intertidal zone)
Continuous immersion zone:               Bare steel or cathodic protection
Below lowest water level.
Underground zone: below the soil         No protection necessary.
line.

12.0       Methods of Contract: Contract procedure - Basic types of
contractual arrangement under which piling may be undertaken.

12.1 Method-1: Railway is responsible for deciding the type or alternative
type of pile, the working loads, and the allowable settlement under test load.
Railway specifies the material to be used, the working stresses, fabrication
methods and penetration depths. Tenders are invited on the basis of a
detailed specification and drawings, accompanied by a site investigation
report, and a site plan showing existing surface levels, proposed regrading
levels, and the operating levels for the piling rigs.

12.2 Method-2: Railway invites tenders for one or an alternative system
of piling from specialist contractors. The invitation to tender is accompanied
by a pile layout showing individual pile loads or column and wall loadings, and
by a detailed specification including such items as materials, working stresses,


                                       35
performance under load test and other criteria of acceptability.       The
contractor decides on the required type (or alternative type) of pile, the
diameter and the penetration depth for the specified working loads, and
bases his tender on his own estimates of performance. Site information as
described for Method 1 should also be supplied.

12.3 Method-3: Railway supplies a drawing to the tendering Contractor
showing the wall and column layout of the structure together with the
loadings; the site information as described for Method 1 is also supplied. No
specification is issued and the Contractor is expected to submit a brief
specification with his tender, and to guarantee the successful performance of
the piles.

12.4 Method-1: has the advantage that the responsibility of each party is
clearly defined. The Contractor has the responsibility only of selecting the
most efficient type of plant to do the job and to install the piles in a sound
manner complying with the specification. The method has the disadvantage
that the knowledge and experience of the Contractor may not be full utilized,
since Railway may not always select the most suitable pile for the job. In
exercising his responsibility or deciding on the pile diameters and penetration
depths, Railway may instruct the Contractor to install preliminary test piles
before making final decisions on the dimensions of the working piles.

12.5 Method-2 provides the widest choice of piling systems and utilizes the
experience of the Contractor to the fullest extent, but greater care is needed
in defining responsibility. In particular, Railway must specify precisely his
requirements for performance under loading tests, both on preliminary and
working piles. While the Contractor is responsible for selecting the type,
diameter and penetration depth of the piles, he should be requested to
submit his calculations for these selections for the approval of the Railway.
The statement concerning working loads on columns, walls or individual piles
should make it clear as to whether or not the loads have been factored in
compliance with the Codal Provisions.

12.6 Method-3 is unsatisfactory in most respects. It is usually stated in
the tender invitation or it is implied that the Contractor assumes responsibility
for all aspects of the work. The Contractor must decide whether or not load
testing is required and the criteria for successful performance under test. The
method can work satisfactorily if Railway invites tenders only from those firms
who have the necessary experience, and can be relied on to act in the best
interests of the Railway.

          However, problems can arise when, because of unforeseen variations
in the ground conditions, the Contractor is obliged to increase substantially the
penetration depth, or to increase the number of piles or even to abandon a
particular system. These problems inevitably lead to claims by the contractor,
and Railway may find it difficult to accept them since it reflects on our ability
in selecting the Contractor.


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12.7 Items of responsibility which must be defined in the
conditions of contract

       The site investigation is undertaken by the Railway before inviting
 tenders for the piling. Railway should include all relevant details in the site
 investigation report in the tender documents. The facilities provided by the
 main contractor, or to be included in the piling contract, should be stated.
 These include such item as access roads, hardstandings for piling plant,
 storage areas, fencing, watching, lighting, and the supply of electrical power
 and water.

       Hardstandings (working platforms) for large piling plant may need to
 be of substantial construction and Railway should state the form in which
 they will be provided including the level of the platform in relation to the pile
 commencing surface and cut-off level. Underground services and
 obstructions can be a contentious item.

       It is normally Railway‟s responsibility to locate all known buried
 services and other obstructions to pile installation. It is unfair to the
 Contractor for the Railway to disclaim all responsibility for the accuracy of
 the location plan, and to expect the contractor to accept the consequences
 of damage to service. The clause in the conditions of contract covering
 underground obstructions needs to be carefully worded to be fair to the
 interests of all parties.

12.8 Piling specifications:        A few matters which require particular
attention are listed below:

(a)    Setting out: The responsibility for setting out is clear if the piling
contractor is the main contractor. If the specification does not define the
responsibility for setting out, the piling sub-contractor must have a clear
understanding with the main contractor on this matter.

(b) Ground heave: In the case of the Method 1 type of contract Railway,
in specifying the type and principal dimensions of the pile, must accept
responsibility for the effects of ground heave.

        However, if the contract is of the Method 2 category the matter is not
so clear, and piling contractors are reluctant to accept responsibility for ground
heave, either for remedial work to risen piles, or for repairing damage to
surrounding structures. It should be clearly defined.

(c)    Loss of ground due to boring:           The responsibilities for these are
similar to those for ground heave.




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(d) Noise and vibration: The Contractor is responsible for selecting the
plant for installing piles and is therefore responsible for the effects of noise
and vibration . If the local authority has regulations limiting noise emissions
these should be stated in specification.

(e)    Piling programme: If Railway wishes to install the piles for the
various foundations in a particular sequence to suit the main construction
programme he should state the sequence in the specification, since it may not
be the most economical one for the piling contractor to follow.

(f)    Tolerance: Tolerances in plan position, vertical deviation from the
required rake, and deviation in level of the pile head, should be specified.

(g) Piling records: Railway should specify the form in which he requires
the Contractor to submit records .

(h) Cutting down pile heads: The specification should define whether it
is the main contractor‟s or the piling contractor‟s responsibility to remove
excess lengths of pile projecting above he nominal cut-off level.

(i)     Method of measurement: The method of measuring pile length as
installed should be defined clearly in the specification.

(j)    Removal of spoil: The respective responsibilities for the removal of
spoil from bored piles, the removal of cut-off lengths of pile, trimming off
laitance and ground raised by ground have, and the disposal of used
bentonite slurry, should be covered in the specification.

13.0 Book of references:-

13.1 Indian Codes

         IS-2911   (Part-I/Sec-1)-1979 Driven Cast in Situ Piles
         IS-2911   (Part-I/Sec-2)-19079 Bored Cast in Situ Piles
         IS-2911   (Part-I/Sec-3)-1979 Driven Precast Piles
         IS-2911   (Part-I/Sec-4)-1979 Bored Precast Piles
         IS-2911   (Part-II)-1980 Timber Piles
         IS-2911   (Part-III)-1980 under Reamed Piles
         IS-2911   (Part-IV)-1985 Pile Load Test
         IS-8009   (Part-II)-1980 Settlement of Deep Foundation

13.2 Foreign Codes

         CP-2004 safety precautions in the construction of large dia
          boreholes for piling and other structures.
         ASTM-D-6760 Cross Hole Sonic Logging for Integrity Testing of
          Piles



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13.3 Web Addresses

         http://www.geoforum.com
         http://www.ndt.net/article/ndtce03/toc.htm#7




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