Volumetric behaviour of clays under freeze–thaw cycles in a mesoscopically uniform element

Abstract

The volume change behaviour of fine-grained soils under repeated freeze–thaw cycles was investigated in context of artificial ground freezing, in which relatively quick freezing is achieved under confinement. Laboratory cyclic freeze–thaw tests with large freezing rates were performed on two clays in two different laboratory set-ups, either with isotropic pressure or with one-dimensional configuration. After freeze–thaw cycles, soils appear to reach residual states unique to each stress level, and the freeze–thaw residual line (FTRL) is defined to represent them. The current soil state's distance to the FTRL, defined as the freeze–thaw state parameter, is well correlated to subsequent volume changes. The one-dimensional freezing set-up provides a correlation more representative of the net effect of freeze–thaw, as all-around freezing under isotropic pressure subjects the specimen to unnatural shear straining. The different nature of freeze–thaw-induced volume changes was observed for high-plasticity Kasaoka clay and low-plasticity kaolin, as characterised by different configurations of the FTRL to the normal compression line. X-ray computed tomography confirmed largely uniform deformation in most of the adopted test conditions, while lower stress and slower freezing led to partial vertical cracking. This type of non-uniformity is shown not to be a main cause of the observed overall freeze–thaw-induced volume changes.