Research on the fracture mode and damage evolution model of sandstone containing pre-existing crack under different stress paths

Abstract

To study the effect of creep loading on the fracture mode and damage evolution process of jointed rock masses during fatigue loading, a series of multilevel cyclic loading and unloading tests (MCT) and fatigue-creep tests (FCT) were carried out on jointed sandstone samples. First, a combined detection platform was built using acoustic emission (AE), scanning electron microscopy (SEM) and digital image-related (DIC) technologies. Then, the fracture mode of the sample is analyzed at the macro- and mesoscale. Finally, based on the loading and unloading response ratio (LURR) theory, assuming that the internal damage of the sample obeys the improved Harris distribution, a damage evolution model of the sandstone sample was established, and the applicability and validity of the model were verified. The test results show that applying creep load during the fatigue loading process can increase the axial strength, reduce the axial deformation, weaken the energy dissipation, and exhibit the phenomenon of early hardening. In terms of fracture mode, applying creep load can change the type of cracks that dominate the failure of the sample, improve the shear resistance, and increase the brittleness when the sample is broken. At the same time, the dislocation movement between the grains, pressure solution and splitting phenomenon will be enhanced, and the types of micro-defects will increase. In terms of the damage evolution process, a short-term low-stress level creep load can reduce the rate of damage growth, thereby increasing the fatigue life of the rock mass.