Study on the mechanical properties and damage constitutive model of frozen weakly cemented red sandstone

Abstract

The freezing method is an effective method for shaft construction in water-rich strata. To determine the mechanical properties of frozen walls that contain ice, study the fracture and instability of frozen rock walls, and solve ice-rock coupling problems, it is necessary to research frozen rock masses under triaxial compressive stress. In this paper, using X-ray diffraction and mesostructure observation, the microstructural characteristics and deformation mechanism of frozen red sandstone specimens taken from the Shilawusu coal mine at a depth of 300 m in the Ordos Basin were studied. A series of tests were performed on frozen red sandstone samples under triaxial compression at 4 temperatures and 4 confining pressures using self-developed DRTS−500 subzero rock triaxial test system. The strength and deformation characteristics of the frozen red sandstone under three-dimensional loading were examined. Test results showed that the bonding water formed by charge adsorption on the surface of the mineral particles and the freezing of pore gravity water enhance the cementation of the mineral particles and the flow plasticity under high stress. At constant temperature, the peak strength and elastic modulus of the frozen red sandstone increase with increasing confining pressure. At constant confining pressure, the peak strength and elastic modulus of the frozen red sandstone increase with decreasing temperature, but temperature has little effect on the peak strain. The internal friction angle of the frozen red sandstone is between 28° and 35° and decreases linearly with decreasing temperature. The cohesion is between 4 and 9 MPa and increases linearly with decreasing temperature. At high freezing temperatures, with an increase in confining pressure, the main factors controlling of the triaxial strength of the rock samples change from the cohesive force to the biting force caused by the mineral particles and ice crystals and the friction between them, and the failure mode of the rock samples changes from tension to shear failure. When the temperature is low, the main controlling factors for sample failure are the cohesive force and friction bite force, and the swelling failure and tension-shear composite failure are the main factors. Based on the parabolic strength criterion and the statistical damage theory derived from the strain equivalence principle, a statistical damage constitutive model that considers the void compaction stage and residual strength deformation stage is established, and the analytical expressions for the model parameters are given, which verify the rationality and validity of the model.