Study on dynamic mechanical characteristics of specimens with cavity under prestressing conditions

Deep defect-bearing rock bodies are typically subjected to in-situ stresses and dynamic loading. This study investigates the failure characteristics of cavity specimens containing square holes and circular holes by employing different static-dynamic coupled loading experiments using a triaxial SHPB device that can facilitate static-dynamic coupled loading. Based on SHPB experiments, strain field analysis, and 3D laser scanning modelling techniques, this study comparatively analyses the effects of impact velocity and stress environment on the strength, stress–strain curve characteristics, dynamic damage process, and damage characteristics of square and circular hole specimens. The experiment proposes using elevation maps to characterise the damage characteristics of the specimen under impact loading. It ultimately relates the experimental results to field rockbursts and tunnel excavation, which has significant implications for guiding field practice to a certain extent. The experimental results showed that the stress environment under dynamic perturbation has a bidirectional effect (both favourable and unfavourable) on the strength of the specimens containing defects, which manifests as a difference in the characteristics of the stress–strain curves. When damage occurs near the cavity of the specimen, the stress–strain curve exhibits type I characteristics. When the entire specimen destabilises, the stress–strain curve shows type II characteristics. Under the same conditions, the strength of the specimens with square holes is significantly lower than those with circular holes. The 3D laser scanning results indicated that the damage is primarily concentrated near the cavity, and compared to the circular hole specimen, the damage area of the square hole specimen is mainly attributed to shear-tension damage, resulting in the collapse of the slabs on the upper and lower sides of the cavity.