Effect of prior cyclic damage on rock failure exposed to triaxial multistage unloading confining pressure and cyclic loads

Abstract

A series of triaxial alternative unloading and damage-controlled cyclic loading tests were conducted on deeply buried granodiorite. The testing results reveal that the prior cyclic loading damage influences rock volumetric deformation, stiffness degradation, damage evolution, and failure modes. Rock volumetric deformation and hysteresis ratio increase with increasing prior cyclic damage, and the subsequent damage propagation is the most severe for a sample subjected to high cyclic damage. A larger hysteresis ratio indicates large plastic deformation and energy loss. In addition, a damage evolution model was proposed based on the irreversible radial strain, and it well describes the damage propagation at the respective cyclic loading stage (CLS) and unloading confining pressure stage (UCPS). Moreover, as prior damage increases, the dominant failure mode changes from shear failure to mixed shear-tensile failure and then to tensile failure. It is suggested that rock failure is cyclic damage dependent; damage fully develops under high cyclic damage.

Acoustic emission characteristics and energy evolution law of rock damage process of different pore structures under cyclic loading

“…Cyclic loading not only causes fatigue damage. It also limits its fatigue behaviour 11 ; Under cyclic loading, more plastic strain and energy loss occurs in the initial loading stage of mudstone, and the damage factor reflects the relationship between fatigue damage and loading 12 ; Different damage models can be built according to acoustic emission parameters for limestone with different rockburst tendencies 13 ; There are significant differences in the AE and fracture modes of marble in different experiments 14 ; Coal, sandstone and shale exhibit different fracture patterns as water velocity increases 15 ; A priori cyclic damage affects the robustness and deformation characteristics of rocks, as well as their failure modes 16 ; Previous repeated loading influences the deformation of the granodiorite volume, the loss of stiffness, the development of damage and the failure mode 17 . The above researchers have carried out extensive research into the mechanical properties and damage characteristics of rocks under the action of external forces.…”