Deformation and strength behaviors of frozen clay with thermal gradient under uniaxial compression

• Local axial strain distribution consists of two typical stages.
• Characteristic parameters depend on the initial test condition.
• Thermal gradient and average temperature influenced compression strength.
• Local strain rate–strength relationship can be well described by a power equation.

Thermal gradient is one of the main features in artificial freezing ground and permafrost regions. The deformation and strength behavior of frozen soils with thermal gradient is of utmost importance for stabilities analysis of frozen engineering. A series of uniaxial compression tests were carried out on frozen saturated clay at various average temperatures and thermal gradients. The experimental results indicated that the uniaxial stress–strain curve for frozen clay with thermal gradient presents elastic-linear strain hardening characteristics, both the hardening modulus and uniaxial compression strength increase as the thermal gradient and average temperature decreased, but the elastic modulus varies little as the thermal gradient increased. The polygonal stress–strain constitutive equations were implemented into the FEM (Finite Element Method) and the local axial strain distribution of frozen clay with thermal gradient was studied. Two stages are observed from the curves describing the relationship between local axial strain and specimen height, i.e., increase stage and decrease stage for the slope of d. Characteristic parameters such as the demarcation height of Hd, the maximum slope of dmax are defined and analyzed. It is found that the characteristic parameters are all dependent on the thermal gradient and average temperature. The thermal gradient presents weakening effects to the local axial strain rate at middle specimen height of δεa,H=10′/δt in frozen clay with identical average temperature, and that further lead to the decrease of hardening modulus and uniaxial compression strength.