Cryostress in Frozen Soil. I: Concept, Definition, and Validation

Abstract

The concept of cryostress in soil is conceptualized, defined, and validated. Force and water potential equilibrium principles at the scale of a soil–water representative elementary volume (REV) are employed to distinguish three types of forces: (1) skeleton forces transmitted through the soil grains and ice; (2) active forces at the interfaces of ice–liquid, ice–soil, liquid–soil, and air–liquid; and (3) passive counterbalancing forces at the phase interfaces and contacts. Forces that arise from the presence of ice are the second type of force and include adsorptive forces between ice and soil, capillary forces between ice and liquid water, and ice bonding forces. These forces are conceptually combined into an REV scale stress called cryostress. Cryostress depends on water content and temperature and thus is a characteristic function for a given soil captured by the cryostress characteristic curve. An effective stress equation for yield behavior is formulated to include cryostress and is validated using measured shear strength data for a variety of soil types under freezing conditions. The shear strength behavior of frozen soil can be uniquely predicted by the classical Mohr–Coulomb failure envelope and confirms the validity and applicability of cryostress as a component of the effective stress. Dependence of cryostress on temperature and a methodology for its determination are demonstrated. The cryostress concept provides a potentially simple and practical way to describe the state of stress in the classical effective stress framework for frozen soil.