ASTM D7760-12

4.1 This test method is used to measure one-dimensional vertical flow of water through initially saturated TDAs under an applied hydraulic gradient. Hydraulic conductivity is required in various civil engineering applications of TDAs.

4.2 TDAs are to be tested at a unit weight and under an overburden pressure representative of field conditions. Data from the literature indicate a reduction in hydraulic conductivity with increasing vertical pressure 4.3 Use of a dual-ring permeameter is included in this test method in addition to a single-ring permeameter. The dual-ring permeameter allows for minimizing potential adverse effects of sidewall leakage on measured hydraulic conductivity of the test specimens. The use of a bottom plate with an inner ring with a diameter smaller than the diameter of the permeameter and two outflow ports (one from the inner ring, one from the annular space between the inner ring and the permeameter) allows for separating the flow from the central part of the test specimen from the flow near the sidewall of the permeameter.

4.4 Darcy's law is assumed to be valid, flow is assumed to be laminar (Reynolds number less than approximately 2000–3000), and the hydraulic conductivity is assumed to be essentially independent of hydraulic gradient. The validity of Darcy's law may be evaluated by measuring the hydraulic conductivity of a specimen at three hydraulic gradients. The discharge velocity (v = k × i) is plotted against the applied hydraulic gradient. If the resulting relationship is linear and the measured hydraulic conductivity values are similar (i.e., within 25 %), then Darcy’s law may be taken as valid.

1.2 A single- or dual-ring permeameter may be used in the tests. A dual-ring permeameter may be preferred over a single-ring permeameter to take into account and prevent short-circuiting of permeant along the sidewalls of the permeameter. The effects of sidewall flow is more significant at high stresses and when the cell diameter is less than 6 times the particle size 1.3 The test method is used under constant head conditions.

1.4 Water is used as the permeant with the test method.

1.5 Test Method D2434 also can be used for determination of hydraulic conductivity of TDAs with sizes smaller than 19 mm under constant head conditions in a rigid-wall permeameter. Method D2434 includes the use of a permeameter with a single ring.

1.6 The standard units for the hydraulic conductivity values are the SI units, unless other units are specified. Hydraulic conductivity has traditionally been expressed in cm/s in the U.S., even though the official SI unit for hydraulic conductivity is m/s.

1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.