Tension limit of frozen clay under unsteady loading and temperature conditions

The tensile strength characteristics of frozen clay were investigated by performing triaxial tension tests, in which the axial total stress was decreased to negative values while zero or positive lateral total stress was maintained. A particular focus was placed on the tensile strength against different loading rates and, more generally, against irregular loading and temperature changes. The test conditions involved insertion of loading pause(s), temperature increase, temperature decrease or both, and variable loading rates. Different combinations of lateral stress and loading rate resulted in the strain at tensile failure ranging widely from around 1% to more than 20%. This variety of ductility has a significant bearing on artificial ground freezing design. An interpretation framework adopting a delayed tensile-degradation concept and temperature-dependent tensile failure lines is proposed to describe the monotonic and non-monotonic loading/temperature tests altogether consistently. The only scenario that is not directly captured by this framework is cooling from relatively warm temperatures (−4°C in this study), which seemingly cancelled the degradation. While describing this scenario accurately still requires continued research, the proposed framework offers a platform for advanced numerical modelling incorporating tensile strength, as well as a practical method for estimating the tensile failure from limited test data.