Mechanical properties and modified binary-medium constitutive model for red-bed soft rock subjected to freeze-thaw cycles

For the deformation and evaluation of red-bed landslides in seasonally frozen ground regions, it is of great significance to study the mechanical properties of red-bed soft rocks subjected to freeze-thaw cycles and to establish an applicable constitutive model. Triaxial tests are conducted on red-bed soft rocks at conditions of different confining pressures and freeze-thaw cycles. The test results demonstrate that the freeze-thaw cycles significantly reduce the strength of the rock and make the ductile damage characteristics more significant. Based on the breakage mechanics for geological materials, the red-bed soft rocks are abstracted into two parts: the structural block and the weak zone. The structural block is transformed into the weak zone when the internal cementation is lost. The binary-medium structure composed of structural blocks and weak zones can reasonably explain the residual deformation mechanism and freeze-thaw damage mechanism of rocks. A constitutive model considering initial freeze-thaw damage is proposed based on the binary-medium structure and homogenization theory. The initial damage caused by the freeze-thaw cycle is reflected by introducing the initial breakage ratio parameter in the model. In addition, the inhomogeneous deformation characteristics of the structural block and the weak zone are reflected by introducing the strain concentration parameter. The model validation results demonstrate that the proposed model can accurately predict the deformation characteristics of red-bed rocks and can successfully reflect the deterioration characteristics caused by freeze-thaw cycles.