A simple framework for describing strength of saturated frozen soils as multi-phase coupled system

Abstract

Frozen soils are characterised by the co-existence of ice and unfrozen liquid water in the pores, engendering complex interactions between thermal, hydraulic and mechanical processes within a coupled system. The consequence is reflected in the peculiar features seen in frozen soils' deformation behaviour and strength. This study applies a re-interpretation to a constitutive modelling framework for frozen soils originally proposed by Nishimura and co-workers in 2009 and demonstrates its expediency in describing some of the key features of frozen soils' strength. The framework adopts a suction-equivalent stress, s, and an effective stress, p′, with a critical state line (CSL) common to both frozen and unfrozen states, following a postulate put forward by Ladanyi and Morel in 1990. The influence of temperature, density and confining pressure application before and after freezing on the ultimate strength is rationally reproduced by simple criteria combining pore ice tensile failure and the CSL within the framework, while it is seamlessly continuous to conventional unfrozen critical state soil mechanics above the freezing temperature. Such complex phenomena as the multi-stage pressure dependency of the frozen strength, originally noted by Chamberlain and co-workers in 1972, are shown to be described generally well for clays and sands.