Experimental study of rate-dependent uniaxial compressive behaviors of two artificial frozen sandy clay soils

Abstract

The rate-dependent uniaxial compressive behavior of frozen clay soil is strongly affected by its minerals, void ratio, stress history, and pore fluid salinity. Previous studies show that an extremely low deformation rate applied on a clay soil tends to result in a lower bound compressive strength. However, the lower bound stress-strain behavior of frozen clay soil under the uniaxial compressive condition was not studied. A thorough understanding of the rate-dependent behavior of frozen clay and its relationship with temperature requires a large number of specimens with similar compositions and micro-structures. In this study, a series of laboratory tests were carried out on artificial frozen sandy clay soils to measure the rate-dependent uniaxial compressive behavior at temperatures ranging from −15 °C to 0 °C. We used two types of artificial frozen clay soils with pre-determined clay fraction, clay mineralogy, stress history, and moisture content. Our results conclude that a low temperature and a high deformation rate tend to generate brittle failure with post-peak softening behavior. A temperature close to the freezing temperature and a low deformation rate result in a diffuse failure associated with strain hardening. Temperature-dependent uniaxial compressive mechanical properties were measured and modeled using empirical relations, which are highly dependent on the applied deformation rate. A series of step-loaded relaxation tests were carried out on those artificial clay soils and creep parameters were estimated using relaxation test results and a power law creep model. A new approach of deriving the lower bound of stress-strain curve of frozen soil is proposed accordingly. The idea of determining the lower bound of stress-strain curve is based on the isotache concept, which was previously used in the soil consolidation theory.