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FIELD PERMEABILITY TEST

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					Pavements & Structures                                                       TEST METHOD   WA 335.1


                                FIELD PERMEABILITY TEST

SCOPE

This method describes the procedure for the field determination of sorptivity, hydraulic
conductivity and modified permeability of a soil. The modified permeability test enables
rapid comparisons of rates of moisture infiltration through soil types or soil horizons.


APPARATUS

1.        Surface permeameter consisting of the following units:

1.1       Perspex base, graduated cylindrical reservoir, rubber stopper.

1.2       Steel surcharge ring.

1.3       Rubber sealing ring.

1.4       Plastic inner ring.

1.5       Small rubber bung.

1.6       Bentonite paste.

1.7       Fast flow filter papers.

2.        Stop-watch.

3.        Worksheets MRD (optional).


PROCEDURE

1.        Test Preparation

1.1       Obtain a test site in accordance with Test Method WA 100.1 (Note a).

1.2       Place sufficient bentonite paste onto the bottom of the rubber ring to ensure a good
          seal.

1.3       Place the rubber ring with the bentonite paste on the test site.

1.4       Insert the plastic inner ring into the rubber ring and using the steel surcharge ring
          apply pressure on top of the rubber ring.

1.5       Scrape of the excess bentonite from inside the rubber ring and remove the steel
          surcharge ring (Note b).

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1.6       Place the small rubber bung into the air inlet hole of the perspex base and invert the
          permeameter.

1.7       Fill the reservoir with water up to the top of the perspex base.

1.8       Place a filter paper on top of the reservoir tube (Note c).

1.9       Invert the water filled permeameter and carefully place it on top of the rubber ring
          making certain it is seated properly (Note d).

1.10      Place the steel surcharge ring around the cylindrical reservoir and seat it on top of the
          perspex base.

2.        Testing

2.1       Determination of Sorptivity and Hydraulic Conductivity.

2.1.1 Remove the rubber bung from the air inlet hole in the perspex base to begin the test.

2.1.2 Take an initial reading of water level and simultaneously start the stop watch, as soon
      as the turbulence ceases and a reading can be determined.

2.1.3 Take readings every 10 seconds for the first 2 minutes to obtain the sorptivity.

2.1.4 Continue to take readings at suitable intervals of time (Note e).

2.1.5 Check for leaks between the sealing ring and the soil surface. If leaks are present
      discontinue the test (Note f).

2.1.6 Continue the test until a steady state infiltration rate is obtained (Note g).

2.1.7 Determine the field dry density in the near vicinity of the sample site in accordance
      with Test Method WA 324.1 or WA 324.2.

2.1.8 Determine the moisture content of the centre of the test area and from material
      adjacent to the test site in accordance with Test Method WA 110.1 or WA 110.2.

2.2       Determination of Modified Permeability.

2.2.1 Remove the rubber bung from the air inlet hole in the perspex base to begin the test.

2.2.2 Take an initial reading of water level and simultaneously start the stop watch, as soon
      as the turbulence ceases and a reading can be determined.

2.2.3 Take readings at suitable intervals of time (Note e).

2.2.4 Check for leaks between the sealing ring and the soil surface. If leaks are present
      discontinue test (Note f).

2.2.5 Continue the test until a steady state infiltration rate is obtained. (Note g).


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Pavements & Structures                                                      TEST METHOD   WA 335.1

CALCULATIONS

1.        Determination of Sorptivity and Hydraulic Conductivity.

1.1       Determine the cumulative flow V, (Note i) of water into the soil after each elapsed
          time by subtracting the water level readings from the initial water level reading.
          Tabulate the cumulative flow against the corresponding elapsed time.

1.2       Multiply V by the calibration factor (Note j) to convert the cumulative flow to cubic
          metres and designate it now as Q.

1.3       Determine the cumulative infiltration after each elapsed time by dividing the
          cumulative flow by the area of the base using the following formula:

                                  Q
                         I   =
                                 π r2

          where          I   = Cumulative infiltration in metres
                         Q   = Cumulative flow in cubic metres
                         r   = Radius of base in metres

1.4       Prepare a table showing cumulative infiltration I, against elapsed time t.

          Determine sorptivity S, by plotting Q/πr2 (m) versus the square root of time in
          seconds. The slope of the linear portion at early time is the sorptivity in m/s½.

1.5       Determine the steady state infiltration rate by plotting Q/πr2 (m) versus time in
          seconds. The slope of the linear portion at long time is the steady state infiltration
          rate, and can be express in metres per second as:

                         q/πr2

          where          q = flow measurement in cubic metres per second.

1.6       Calculate the initial volumetric moisture content expressed as a ratio σ n by using the
          following formula:

               Dry Densityof soil(t/m 3 ) x InitialM.C(%)
          σn =
                                 100

1.7       Calculate the final volumetric moisture content expressed as a ratio σ 0 by using the
          following formula:

                  Dry Density of soil (t / m3 ) x Initial M.C(%)
          σ0 =
                                       100




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1.8       Calculate Hydraulic Conductivity using the formula:

                   2rS 2 
          K = q -           /π r 2
                  σ0 −σ n 
                           

          where          K     =   Hydraulic Conductivity in m/s
                         q     =   Flow measurement converted to m3/s
                         r     =   Base radius in m
                         S     =   Sorptivity in m/s½
                         σ0    =   Final volumetric moisture content expressed as a ratio
                         σn    =   Initial volumetric moisture content expressed as a ratio

2.        Determination of Modified Permeability

2.1       Determine the cumulative flow V (Note i) of water into the soil after each elapsed time
          by subtracting the water level readings from the initial water level reading. Tabulate
          cumulative flow against the elapsed time.

2.2       Multiply V by the calibration factor (Note j) to convert the cumulative flow to cubic
          metres Q.

2.3       Determine the cumulative infiltration I, after each elapsed time by dividing the
          cumulative flow by the area of the base using the following formula:

                         I =       Q/πr2

          where          I =       Cumulative infiltration in cubic metres
                         Q =       Cumulative flow in metres
                         r =       Radius of base in metres

2.4       Graph the cumulative infiltration rate in metres versus the time in seconds and
          determine the modified permeability Kmod as the slope of the linear portion of the
          graph, ie., the change in I divided by the change in t.


REPORTING

1.        Report the following values:

1.1       Hydraulic conductivity (m/s).

1.2       Sorptivity (m/s½).

1.3       Initial and final volumetric moisture contents expressed as ratios.

1.4       Modified permeability (m/s).




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Pavements & Structures                                                                 TEST METHOD      WA 335.1
2.        The following general information may be reported as appropriate:

2.1       Identification and description of the sample site.

2.2       Location of the sample site.

2.3       Proposed use of material tested.

2.4       Depth of test site.

2.5       Date test performed.


NOTES

(a)       The site should be as level and as even as possible to prevent problems with water leaking past the
          rubber sealing ring.

(b)       Care should be taken that the surface to be tested does not become contaminated with bentonite.

(c)       The diameter of the filter paper should be slightly larger than that of the reservoir tube.

(d)       Atmospheric pressure acting on the filter paper prevents loss of water when the tube is inverted.

(e)       The time interval between readings is dependent on soil type.

          The following may be used as a guide:

                10 -     30 seconds for sands
                1 -      5 minutes for gravels
                5 -      30 minutes for clays

(f)       In some instances leaks can be stopped by applying more bentonite around the rubber sealing ring. If
          this fails a new test site is required.

(g)       The progress of the test should be monitored by plotting the readings against time. The test is
          terminated when a straight line is obtained.

(h)       The cumulative flow is the total quantity of water that has flowed into the soil at any given time.

(i)       The cumulative flow is the total quantity of water that has flowed into the soil at any given time.

(j)       The calibration factor is determined by calibrating the cylindrical reservoir. A known mass of water is
          poured into the reservoir and the column of water is measured by the graduations on the reservoir. The
          mass of water is divided by the number of graduations to give the calibration factor.




MAIN ROADS Western Australia                      Field Permeability Test                               Page 5 of 5
T\WA335.1                                        Test Method 71/02/335.1
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