ASTM D6035-08

This test method identifies the changes in hydraulic conductivity as a result of freeze-thaw on natural soils only.

It is the user's responsibility when using this test method to determine the appropriate moisture content of the laboratory-compacted specimens (that is, dry, wet, or at optimum moisture content) (Note 2).

Note 2—It is common practice to construct clay liners and covers at optimum or greater than optimum moisture content. Specimens compacted dry of optimum moisture content typically do not contain larger pore sizes as a result of freeze-thaw because the effects of freeze-thaw are minimized by the lack of water in the sample. Therefore, the effect of freeze-thaw on the hydraulic conductivity is minimal, or the hydraulic conductivity may increase slightly. ^,

The requestor must provide information regarding the effective stresses to be applied during testing, especially for determining the final hydraulic conductivity. Using high effective stresses (that is, 35 kPa (5 psi) as allowed by Test Method D 5084) can decrease an already increased hydraulic conductivity resulting in lower final hydraulic conductivity values. The long-term effect of freeze-thaw on the hydraulic conductivity of compacted soils is unknown. The increased hydraulic conductivity caused by freeze-thaw may be temporary. For example, the overburden pressure imparted by the waste placed on a soil liner in a landfill after being subjected to freeze-thaw may reduce the size of the cracks and pores that cause the increase in hydraulic conductivity. It is not known if the pressure would overcome the macroscopically increased hydraulic conductivity sufficiently to return the soil to its original hydraulic conductivity (prior to freeze-thaw). For cases such as landfill covers, where the overburden pressure is low, the increase in hydraulic conductivity due to freeze-thaw will likely be permanent. Thus, the requestor must take the application of the test method into account when establishing the effective stress.

The specimen shall be frozen to −15°C unless the requestor specifically dictates otherwise. It has been documented in the literature that the initial (that is, 0 to −15°C) freezing condition causes the most significant effects in hydraulic conductivity. Freezing rate and ultimate temperature should mimic the field conditions. It has been shown that superfreezing (that is, freezing the specimen at very cold temperatures and very short time periods) produces erroneous results.

The thawed specimen temperature and thaw rate shall mimic field conditions. Thawing specimens in an oven (that is, overheating) will produce erroneous results.

Literature relating to this subject indicates that the effects of freeze-thaw usually occur by Cycle 10, thus it is recommended that at least 10 freeze-thaw cycles shall be performed to ensure that the full effects of freeze-thaw are measured. If the hydraulic conductivity values are still increasing after 10 freeze-thaw cycles, the test method shall be continued (that is, more freeze-thaw cycles shall be performed).

Note 3—The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D 3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D 3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D 3740 provides a means of evaluating some of those factors.

1.1 This test method covers laboratory measurement of the effect of freeze-thaw on the hydraulic conductivity of compacted or intact soil specimens using Test Method D 5084 and a flexible wall permeameter to determine hydraulic conductivity. This test method does not provide steps to perform sampling of, or testing on, in situ soils that have already been subjected to freeze-thaw conditions.

1.2 This test method may be used with intact specimens (block or thin-walled) or laboratory compacted specimens and shall be used for soils that have an initial hydraulic conductivity less than or equal to 1E-5 m/s (1E-3 cm/s) (Note 1).

Note 1—The maximum initial hydraulic conductivity is given as 1 E-3 cm/s. This should also apply to the final hydraulic conductivity. It is expected that if the initial hydraulic conductivity is 1 E-3 cm/s, then the final hydraulic conductivity will not change (increase) significantly (that is, greater than 1 E-3 cm/s).

1.3 Soil specimens tested using this test method can be subjected to three-dimensional freeze-thaw (herein referred to as 3-d) or one-dimensional freeze-thaw (herein referred to as 1-d). (For a discussion of one-dimensional freezing versus three-dimensional freezing, refer to Zimmie or Othman. )

1.4 Soil specimens tested using this test method can be tested in a closed system (that is, no access to an external supply of water during freezing) or an open system.

1.5 The values stated in SI units are to be regarded as the standard, unless other units are specifically given. By tradition, it is U.S. practice to report hydraulic conductivity in centimetres per second, although the common SI units for hydraulic conductivity are metres per second. The values are to be calculated and reported in accordance with Practice D 6026.

1.6 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.