Abstract: Calcium clay layers are widely distributed in the Huainan-Huaibei mining area, with the characteristics of low freezing point, strong frost heave, easy disintegration upon contact with water, and low strength, posing a severe challenge to construction using freezing methods. To investigate the mechanical response of frozen calcareous clay under complex stress paths, true triaxial compression tests were performed on the ZSZ-2000 frozen soil true triaxial test platform, varying confining pressures, temperatures, moisture contents, and intermediate principal stress ratios. The strength and deformation characteristics of frozen calcareous clay under these varying conditions were analyzed. The test results indicate that the strength of frozen calcareous clay has a good quadratic relationship with the intermediate principal stress coefficient b and confining pressure, is negatively correlated with temperature, and positively correlated with moisture content. Furthermore, the rate of increase in the failure strength of frozen calcareous clay decreases as the moisture content rises. The failure strength is significantly influenced by the intermediate principal stress and confining pressure, showing both strengthening and weakening effects. A critical intermediate principal stress coefficient of b_c =0.75 and a critical confining pressure of σ_3c=3 MPa were identified. As the confining pressure rises, the volumetric strain gradually shifts from initial shear contraction followed by shear dilation to pure shear contraction. Moreover, as the b value increases, the peak volumetric strain of the samples also increases. Based on the experimental results, an improved Duncan-Chang model was developed, taking into account the effects of temperature, moisture content, and intermediate principal stress coefficient, and its reliability was verified. The research findings provide a theoretical foundation for optimizing frozen wall design and deep shaft excavation using freezing methods.

Key words: frozen clay, intermediate principal stress coefficient, strength evolution law, true triaxial stress path, Duncan-Chang model