Numerical simulation of the meso-mechanical properties of double cruciform fissures rocks after freeze–thaw cycles

Abstract

Investigating the mechanical properties and microscopic damage behavior of fissured rock masses subjected to freeze–thaw (F-T) cycles is essential for informing stability evaluation and disaster prevention strategies in geotechnical engineering within cold regions. In this study, a numerical simulation model of rock mass specimens with double cruciform fissures was developed applied PFC^2D, and uniaxial compression strength (UCS) tests were performed until the F-T cycles of 10, 20, 30, and 40 values for strength variation and damage characteristics assessed. The results indicate a distinct trend in damage evolution: Tensile cracks predominate during the early F-T cycles, while the proportion of shear cracks increases significantly with the number of cycles, rising from 5.89% at 0 cycles to 17.95% subjected to 40 cycles. A comparison of the cracks evolution in rock specimens between 0 and 40 F-T cycles at various inclinations revealed that the damage initially occurs at the tips of prefabricated fissures. After 40 F-T cycles, damage at these tips intensified markedly, accompanied by numerous surface cracks on rock specimens experiencing freeze–thaw deterioration. UCS tests on the models demonstrated that when only one fissure is altered, peak stress exhibits an N-shaped variation relative to changes in the fissure angle, with relatively small variances (4.77 for peak stress variance and 0.04 for modulus variance). In contrast, when both fissures are adjusted simultaneously, variances increase sharply to 12.9 and 0.16, respectively; maximum strength occurs at angles of 30° and 75°, while minimum values are observed at angles of 15° and 60°. Finally, force chains and stress distribution within the rock samples were predominantly concentrated around the fissures and shifted responsively according to alterations in loading stress and fissure angle; following damage occurrence, a low-stress zone developed near the fissures which expanded as the angle increased.