Damage characteristics and failure modes of deep sandstone under unloading disturbance: Insights from true triaxial test and DEM simulation

Abstract

This study conducted true triaxial unloading disturbance tests and DEM numerical simulations to elucidate the damage evolution and failure modes of deep rock mass under unloading disturbance conditions. The findings indicated that the DEM-developed Model Predictive Control (MPC) method surpasses conventional servo control in stability of servo speed and boundary stress. During initial loading of intact sandstone under high true triaxial stress, stress-coupling characteristics in intermediate/minimum principal stress directions showed insensitivity to intermediate principal stress; divergence began at yield initiation. Perforated sandstone exhibited consistent failure modes across disturbance amplitudes. Increased disturbance amplitude reduced bearing strength while accelerating damage rates, with sixth-level disturbance accounting for >40% of total damage. Tensile cracks consistently predominated over shear cracks throughout loading; disturbance did not significantly alter their ratio. Secondary loading progressively increased shear crack proportion, peaking at specimen failure. Shear failure dominated perforated sandstone instability. Based on the failure characteristics and strength attenuation laws of perforated sandstone under deep disturbance, control measures for engineering sites are proposed. The research results provide a reference for the application of discrete element method in understanding complex stress paths in deep geotechnical engineering and the damage and failure mechanisms of surrounding rock in deep roadways.

Keywords

unloading and disturbance / DEM servo mechanism / perforated sandstone / disturbance damage / deep roadways

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