Burial depth-dependent failure behavior and stress shielding effect of straight-wall semicircular arch holes: a true triaxial experimental study

Straight-walled semicircular arch sections are widely used in deep underground engineering, and the stability of the surrounding rock is of great importance. In this paper, specimens containing straight-walled semicircular holes were taken as the research object. A true triaxial test system was used to simulate the failure characteristics of the surrounding rock around the holes under different burial depths, and the influence of burial depth on the strength evolution and macroscopic failure mode of the surrounding rock was revealed. The results show that as burial depth increases, the specimen strength increases nonlinearly and then tends to stabilize, the depth of the failure zone increases significantly, the angle of the V-shaped failure zone first increases and then decreases, the rotation angle on both sides of the failure zone decreases, and the dominance of crack evolution shifts from geometric defects to the stress field. Mesoscopic analysis reveals that the tensile fracture under shallow burial transitions into a shear-friction composite fracture under deep burial, providing a micromechanical basis for macroscopic failure. Based on the above results, the concept of dynamic evolution of the hole stress shielding effect is proposed. It is noted that this phenomenon involves deformation self-organization, which dynamically evolves with confining pressure, and its essence lies in the dynamic evolution process of stress transmission and energy distribution. Based on this, a three-stage evolution law of weak shielding at shallow burial, strong shielding at deep burial, and shielding failure at ultra-deep burial is established. Based on this law, the functional positioning and cooperative logic of active and passive support under different burial depths are clarified, which provides systematic theoretical support and technical guidance for the stability control of surrounding rock in deep underground engineering.