Cyclical closed-system freeze–thaw permeability testing of soil liner and cover materials

Abstract

The impact of closed-system freeze–thaw cycles on the permeability of clay, till, and sand–bentonite mixtures was examined in a laboratory test program. The bentonite content of the sand–bentonite mixtures varied from 4.5 to 25%. Test samples were prepared by dry mixing, moisture conditioning, and compacting materials according to ASTM D698, method A specifications. The molding water content of these samples was at or slightly wet of optimum. Trimmed test samples were placed in a triaxial permeameter and their unfrozen or initial permeability was established. These permeability tests were conducted for approximately 10 000 min using low hydraulic gradients and confining stress. Changes in specimen volume were also measured during permeability testing. Once the initial permeability of a specimen was established, the test was halted and the specimen was frozen inside the permeameter with no access to water. After freezing, the specimens were allowed to thaw before a second permeability test was conducted. This process of alternating permeability tests with freeze–thaw cycles was continued until the change in permeability between freeze–thaw cycles became insignificant. The results of this test program show that the permeabilities of both the clay and till specimens increase due to freeze–thaw cycles. In contrast, the sand–bentonite specimens showed no increase in permeability due to freeze–thaw cycles. Key words: closed system, freeze–thaw, permeability, volume change, soil liners, soil covers.