Interpretation of mechanical behavior of frozen clay through parallel tests of frozen and unfrozen soils

Abstract

This study reports a fundamental experimental program that aims to propose an approach towards developing a descriptive framework that extends the concept of effective stress and viscoplasticity to frozen states. A series of triaxial compression tests was conducted on reconstituted Kasaoka Clay at different temperatures (three temperatures below the freezing temperature and one above it) and strain rates. The specimens were isotropically normally consolidated to 100, 200 or 400kPa before freezing and sheared at constant strain rates of 10 -3 , 10 -4 and 10 -5 min -1 after the test temperature got stabilized. The observed behavior was interpreted through comparisons with that of unfrozen specimens, which were subjected to a same strain path as that for the frozen specimens through consolidation and swelling corresponding to the volumetric changes due to pore water phase changes. The strength of frozen specimens, as well as being far larger than that of unfrozen specimens, showed much more significant dependence on the strain rate, which is probably due to the presence of the ice. In light of Ladanyi and Morel's (1990) hypothesis on the uniquely related strain path and effective stress path of both frozen and unfrozen states of the same soils, the "effective stress paths" followed by the soil skeleton of the frozen soil were probed by the carefully controlled parallel tests on the frozen and unfrozen states. The Critical State Lines (CSLs) at different temperatures were thus plotted based on the envisaged effective stress paths. The above characterization of frozen and unfrozen soils is expected to lead to construction of a unified framework for describing the behaviors of both states.