Triaxial Mechanical Behavior and Strength Model of Basalt Under Freeze–Thaw Cycling: Implications for Engineering Structures in Cold Regions

Abstract

Previous freeze–thaw studies have mainly used uniaxial tests, leaving the effects of freeze–thaw damage and confinement on basalt behavior and physically interpretable triaxial strength estimation insufficiently resolved. Here, saturated basalt specimens subjected to 0, 10, 20, and 30 freeze–thaw cycles were tested under confining pressures of 0–40 MPa using a triaxial compression system. Stress–strain responses, failure modes, deviatoric stress strength, and Mohr–Coulomb parameters were analyzed; planar, binary quadratic, and freeze–thaw-dependent Mohr–Coulomb models were developed and compared. Freeze–thaw cycling intensified initial compaction and post-peak softening, whereas confinement shifted failure from axial splitting to shear-dominated or mixed modes. After 30 cycles, deviatoric stress strength decreased by 53.6% under uniaxial loading and by 41.1% at 40 MPa confinement; cohesion decreased by 46.2%, from 39.6 to 21.3 MPa, and the internal friction angle decreased from 30.84° to 27.04°. The Mohr–Coulomb model achieved a maximum absolute error of 10.2 MPa, a mean absolute error of 4.7 MPa, and a root-mean-square error of 5.6 MPa. Within 0–30 cycles and 0–40 MPa confinement, the model provides strength estimates for parameter selection and stability assessment of basalt engineering structures in cold regions.