Macro-micro damage model of the effect of freeze–thaw on jointed rocks considering compaction deformation

Abstract

Jointed rock mass contains microscopic cracks, joints and other defects. Moisture migration during freeze–thaw cycles affects crack initiation and propagation of defects of different scales. The change of defects in turn affects the mechanical and deformation properties of jointed rock mass, especially in the compaction deformation stage. Considering the effects of freeze–thaw cycles on compaction deformation, plastic deformation, macroscopic damage and microscopic damage, a macro–micro damage constitutive model of jointed rock mass under freeze–thaw actions was proposed under the framework of thermodynamics. Based on the internal state variables (ISV) theory, the Helmholtz free energy of jointed rock mass under freeze–thaw actions was obtained by taking compaction deformation, macroscopic damage and microscopic damage as internal state variables. The compaction, elasticity, plasticity, and damage stages were analyzed respectively, and the macro–micro damage model of jointed rock considering compaction deformation were deduced by regarding the total strain as three parts (compaction deformation, elastic deformation and plastic deformation). The validity of the proposed model was verified by compression tests on rock samples with different induced crack inclination angles that have undergone different amounts of freeze–thaw cycles. The model considers the moisture migration mechanism of freeze–thaw damage and the friction and slip mechanism of microcrack surfaces. The effect of moisture migration on the compaction deformation during freeze–thaw cycles is significant, and the proposed model can accurately simulate the full stress–strain curves (compaction-elasticity-plasticity-damage) of jointed rock mass under freeze–thaw actions, which provides quantitative guidance for reducing freezing damage by attenuating moisture migration.