Failure of Partially Saturated Frozen Soils: A Micromechanical Analysis

Modelling the mechanical behaviour of partially saturated soils requires special treatment due to interactions among solid, water and air phases. The issue extends also to frozen soils in which ice forms cohesive bridges between soil particles. This study develops a micromechanically based failure criterion for shear strength of partially saturated frozen soil that relates the macroscopic strength of frozen soils to their particle-scale characteristics. Assuming idealized spherical particles, the strength of individual ice bonds is calculated from their geometry and the intrinsic strength of ice. Following a homogeneous stress assumption, a relation between the macroscopic stresses and the interparticle forces is formulated, which eventually leads to a failure criterion at the macroscopic level in terms of parameters such as ice strength, matric suction, void ratio, average particle size, and contact fabric. Other dependencies of the ice strength on parameters such as temperature and strain rate are also naturally captured. The predictions are compared to three different experimental datasets where the model demonstrates good accuracy without any retrospective calibration. Crucially, the failure model establishes a connection between strength of soil at frozen and unfrozen states, which can be used in estimating the strength degradation in frozen soils upon thawing.