On limit strength of frozen clay undergoing triaxial tension

A new interpretation of failure of frozen clay in tension is presented, through a unique test program applying ‘triaxial tension’, in which the axial stress was reduced to negative values while zero or positive radial stress was maintained. The limit strength is determined by a meeting point of two competing mechanisms – strain-hardening in shear, and progressively degrading tensile strength as the shear deformation disturbs the soil structure. In some conditions, the limit strength observed in tension is actually given by the shear resistance limit, not by a true tensile strength. This interpretation is successful in explaining apparently unclear confining stress-dependency of the observed failure envelopes at low stresses. The influence of the pre-freezing effective stress, post-freezing total stress and pre-freezing pore water pressure on the strength was also investigated. The tensile strength degradation was formulated by using the specific work input to estimate the operational tensile strength and the strain at which a tensile rupture occurs. Cooling after shear deformation apparently healed the damage and recovered the initial tensile strength, allowing the stress-strain curve to significantly overshoot the proposed tensile strength line. Explaining the combined influence of shear and temperature history on the tensile strength – work relationships requires further study.