N.J. Admin. Code § 7:9A-6.2 - Tube permeameter test

Current through Register Vol. 54, No. 7, April 4, 2022

(a) The following equipment is required for the tube permeameter test:
1. A thin-walled (one millimeter or less in thickness) metal tube, from one and one-half to three inches in diameter, six inches in length, beveled on the lower outside edge;
2. A wooden block with dimensions broader than the diameter of the tube in (a)1 above and a hammer, to drive the tube into the soil;
3. A small trowel;
4. A knife (to trim core);
5. Muslin or similar open-textured cloth and a rubberband;
6. A soaking basin of adequate size and depth to soak cores as prescribed in (c) below;
7. Fine gravel (from two to 10 millimeters in diameter);
8. A test basin of adequate length (generally 10 inches or greater) and width (generally four inches or greater) to accommodate one or more replicate samples at a time. The depth of the basin should be adequate to allow placement of the sample on a layer of gravel while keeping the bottom of the core several inches below the rim of the basin, as prescribed in (d) below (See Figure 5 of Appendix A);
9. A stopper which fits water-tight into the top of the sample tube and which is fitted with a glass standpipe from three to five inches long and from 0.25 to 0.75 inches in diameter (See Figure 5 of Appendix A). The standpipe should have a scale for measuring changes in water level over time as required in (d) below;
10. A small laboratory wash bottle for refilling standpipe;
11. A clock or watch with second hand;
12. A ruler (engineering scale is best);
13. One gallon of water per test. The water should be allowed to stand in an open container until clear of dissolved air. Boiling may be used to remove air provided that the water is allowed to cool down to room temperature before use; and
14. A two millimeter sieve.
(b) When the tube permeameter test is used, undisturbed samples shall be collected as prescribed in (d) below. When the texture of the soil to be tested is a sand or loamy sand and lack of soil cohesion or the presence of large amounts of coarse fragments, roots or worm channels prevent the taking of undisturbed samples, disturbed samples shall be taken as prescribed in (e) below. When the texture of the soil is other than a sand or loamy sand and undisturbed samples cannot be taken, the tube permeameter test shall not be used.
(c) When the tube permeameter test is used, a minimum of two replicate samples shall be taken and the procedures outlined in this section shall be followed for each replicate sample to be tested. It is recommended that more than two replicate samples be taken to avoid the necessity of re-sampling in the event that samples are damaged in transport or the results of one or more replicate tests must be rejected due to extreme variability of results, as required in (i) below. Replicate samples shall be taken from within the same soil horizon at the same location within the area of the proposed disposal field.
(d) The following procedure shall be used to collect each replicate sample:
1. Step One: Expose an undisturbed horizontal surface within and a minimum of three inches above the bottom of the soil horizon or layer to be tested.
2. Step Two: Position the sampling tube on the soil surface at the point chosen for sampling. Care should be taken to avoid large gravel or stones, large roots, worm holes or any discontinuity which might influence results. If the soil is excessively dry it may be moistened, but not saturated, provided that the force of falling water is not allowed to act directly upon the soil surface.
3. Step Three: Hold the wooden block on the top of the sampling tube and drive the tube into the soil a distance of from two to four inches (but not entirely through the horizon) using light even blows with the hammer. Care should be taken to hit the block squarely in the center and to drive the tube straight down into the soil. Do not attempt to straighten the tube by pushing or by hitting the tube on the side with the hammer.
4. Step Four: When the tube has been driven to the desired depth, carefully remove the soil around the outside of the tube, insert a trowel into the soil below the tube and, exerting pressure from below, lift the sampling tube out of the soil.
5. Step Five: Trim the bottom of the soil core flush with the sampling tube using a knife and taking care not to smear the soil surface. Carefully invert the sampling tube and tap the side lightly with the handle of the knife or similar implement to remove any loose soil which may be resting on the top of the soil core and to verify that an undisturbed sample has been obtained. Omit this step in the case of sandy-textured non-cohesive soils with single grain structure. Check the top and bottom surfaces of the core sample and discard any sample which has worm holes or large cracks caused by handling.
6. Step Six: After the core has been checked for worm holes or signs of disturbance, stretch a piece of muslin cloth over the bottom of the tube and secure with a strong rubberband.
(e) The following procedure shall be used for the collection of disturbed samples for the tube permeameter test:
1. Step One: Collect an adequate volume of the soil or fill material to be tested. Spread the soil on a clean surface and allow to dry in the air until dry to the touch. An oven may be used to accelerate drying provided that the soil is allowed to cool down to room temperature before testing.
2. Step Two: Pass the soil through a two millimeter sieve to remove gravel and stones.
3. Step Three: Stretch a piece of muslin cloth over the bottom of the sampling tubes and place the tubes on a flat surface. Slowly pour the soil into each sampling tube while gently tapping the side of the tube with a hard instrument. Fill the tubes to a depth of three to four inches. Check the bulk density of the sample by dividing the weight of the sample (weight of sample tube containing sample minus the weight of empty sample tube) by the volume of the sample (length of sample multiplied by 3.14 r[LESS THAN]2[GREATER THAN], where r is the internal radius of the sample tube). The minimum acceptable bulk density for disturbed samples is 1.2 grams per cubic centimeter.
(f) The following procedure shall be used for pre-soaking undisturbed or disturbed core samples for the tube permeameter test:
1. Step One: Place the soil core in the pre-soak basin and fill the basin with water to a point just below the top of the soil core. Never fill the basin to a level which is higher than the top of the soil core. Never use water directly from the tap to soak cores. Use only de-aired water as prescribed in (a)13 above. Allow the sample to soak until the top surface of the core is saturated with water. This may require only a few minutes of soaking for sandy textured soils or several days for clay textured soils. Failure to soak the sample for sufficient time may result in greatly reduced permeability measurements due to entrapped air.
2. Step Two: When the sample has soaked for sufficient time, place a one inch layer of fine gravel (from two to 10 millimeters in diameter) on top of the soil core in the sampling tube. Slowly fill the tube with de-aired water taking care not to disturb the surface of the core. A small spatula or similar implement may be used to break the fall of the water as it is poured into the tube.
3. Step Three: Immediately transfer the soil core to the test basin in which a layer of gravel has been placed and gently press the soil core into the gravel so that it stands vertically with its base positioned at the desired depth below the rim of the test basin.
(g) The following procedure shall be used to conduct the tube permeameter test:
1. Step One: When the soil core has been positioned at the desired height within the test basin (see Figure 5 of Appendix A), fill the test basin to overflowing with de-aired water. (Note: The hydraulic head used in the test depends upon the height of the top of the sample tube or standpipe above the rim of the test basin as shown in Figure 5. In general, a higher hydraulic head should be used for heavy textured soils to expedite the test and a lower head should be used for sandy textured soils to prevent an excessively fast flow rate).
2. Step Two: Fill the tube to overflowing with de-aired water and record the time, in minutes, required for the water level in the tube to drop a standard distance such as one-half inch, one inch, or two inches. Repeat this step until the rate of fall becomes constant or the difference between the highest and lowest of three successive readings is less than five percent. When the readings are less than 20 minutes in length the time should be reported to the nearest second.
3. Alternate Step Two: When the rate of fall observed in "Step Two" ((g)2 above) is slow, the flow rate may be increased by use of a standpipe as shown in Figure 5. Carefully insert the standpipe into the top of the sample tube and fill with de-aired water. The apparatus should be checked for leaks where the standpipe fits into the sample tube. Silicon jelly, petroleum jelly or a similar material may be used to prevent leakage. Measure the rate of fall of the water level in the standpipe as in Step Two.
(h) The permeability of each replicate sample tested shall be calculated using the following formula:
1. K (in/hr) = 60 min/hr x L(in)/T(min) x r[LESS THAN]2[GREATER THAN]/R[LESS THAN]2[GREATER THAN] x 1n (H[1]/H[2])

Where:

K is the permeability of the soil sample;

L is the length of the soil core, in inches;

T is the time, in minutes, required for the water level to drop from H[1] to H[2] during the final test interval;

r is the radius of the standpipe, in centimeters or inches;

R is the radius of the soil core, in the same units as "r";

1n is the natural logarithm

H[1] is the height of the water level above the rim of the test basin at the beginning of each test interval, in inches; and

H[2] is the height of the water level above the rim of the test basin at the end of each test interval, in inches.

Note: When the standpipe is not used, the term r[LESS THAN]2[GREATER THAN]/R[LESS THAN]2[GREATER THAN] is omitted from the equation.

(i) Variability of test results shall be evaluated as follows:

Measured Permeability Soil Permeability
Greater than Class
20 inches per hour ("in/hr") K5
6-20 in/hr K4
2-6 in/hr K3
0.6-2 in/hr K2
0.2-0.6 in/hr K1
Less than 0.2 in/hr K0
2. The variability of soil permeability test results shall be considered acceptable only where the results of all replicate tests fall within one soil permeability class or two adjacent permeability classes.
3. Where the results of replicate tests differ by more than one soil permeability class, the samples shall be examined for the following defects:
i. Cracks, worm channels, large root channels or poor soil tube contact within the sample yielding the highest permeability value(s);
ii. Large pieces of gravel, roots or unsaturated soil within the interior of the sample yielding the slowest permeability value(s); or
iii. Smearing or compaction of the upper or lower surface of the sample yielding the lowest permeability value(s).
4. If any of the defects described in (i)3 above are found, the defective core(s) shall be discarded and the test repeated using a new replicate sample for each defective replicate sample.
(j) When test results have been obtained with an acceptable range of variability as defined in (i) above, the results shall be interpreted as follows:
1. When the purpose of the test is to determine the design permeability at the level of infiltration, the slowest of the test replicate results shall be used for design purposes.
2. When the purpose of the test is to identify a hydraulically restrictive horizon or substratum above the water table, the horizon or substratum in question shall be considered hydraulically restrictive if the average permeability of the replicate samples tested falls within soil permeability class KO as defined in (i)1 above.
3. When the purpose of the test is to identify an excessively coarse horizon or substratum above the water table, the horizon or substratum in question shall be considered excessively coarse if the average permeability of the replicate samples tested falls within permeability class K5 as defined in (i)1 above.
(k) Where results of replicate tests exceed the limits of variability allowed in (i)2 above, the results shall be interpreted as follows:
1. When the purpose of the test is to determine the design permeability at the depth of infiltration, the slowest of the test replicate results shall be used for design purposes.
2. When the purpose of the test is to identify a hydraulically restrictive horizon or substratum above the water table, the horizon or substratum in question shall be considered hydraulically restrictive if the slowest permeability of the replicate samples tested falls within soil permeability class KO as defined in (i)1 above.
3. When the purpose of the test is to identify an excessively coarse horizon or substratum above the water table, the horizon or substratum in question shall be considered excessively coarse if the fastest permeability of the replicate samples tested falls within permeability class K5 as defined in (i)1 above.

Notes

N.J. Admin. Code § 7:9A-6.2

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