Macro-micro failures of shear creep and creep damage model of deep hard rocks induced by initial disturbances

Abstract

In deep rock engineering, rock masses under high in-situ stress and mining disturbances typically incur a certain extent of initial damage, which significantly challenges the project’s long-term stability. To study the influence of initial local impact disturbances on the shear creep characteristics of deep hard rocks, shear creep tests on gneiss with different initial disturbance frequencies and impact areas were carried out by using the independently developed rock local impact disturbance − shear creep coupling test device, SEM, and NMR system. Based on the Kachanov creep damage theory, the creep damage variable was defined by the T2 spectral and shear modulus, and a rock shear creep damage constitutive model considering the influences of initial disturbance damage and accelerated creep damage was established. The results demonstrate that the initial local impact disturbances cause obvious changes in the T2 spectrum, leading to the enhancement of the connectivity of the original pores and the deterioration of the internal structure. The microscopic morphology becomes complex, and the strength of the crystal binders is reduced, resulting in a sharp decline in the mechanical properties of the rocks. The factors of disturbance frequency and impact area have weakened the shear strength of gneiss by 3.3% to 12.9% and 5.1% to 18.3% respectively. Therefore, the initial local impact disturbances can accelerate the induction of rock failures and have an important impact on the duration of failures. The shear creep model established herein accounts for the initial disturbance damage of the rocks. The test data exhibits a high level of congruence with the theoretical curve of the model, which is capable of effectively reflecting the creep characteristics of deep gneiss. This model can furnish a theoretical foundation for the establishment of an early warning system in practical deep rock engineering.