Mechanical Response Characteristics and Stability Evaluation of Surrounding Rock in Complex Stratum Excavation of Kilometer Deep Shaft

Currently, the mining depth of underground metal mines in China is progressing beyond 1000 m, transitioning from shallow excavations to deep operations that face complex stratigraphic conditions, high stress, and other challenges. The stability of the shaft wall during both the construction and operational phases is crucial to the overall safety and stability of the entire mine. Rock mechanical parameters serve as the most direct representation of complex stratigraphic conditions. This paper focused on a proposed deep shaft in a mine in Shandong, which was planned to exceed 1000 m in depth and encounter complex stratigraphic challenges. It proposed a method for estimating the stability of the surrounding rock based on the influence of rock mechanical parameters, providing theoretical support for maintaining shaft stability during the construction period. FLAC3D numerical simulation was used to investigate the influence of variations in key rock mechanical parameters on the stability indices of the surrounding rock in a deep vertical shaft. The study results indicate that as rock parameters increase, the location of the maximum displacement of the surrounding rock gradually shifts toward the direction of the initial maximum principal stress. When the uniaxial compressive strength is below 85.93 MPa, the RMR is less than 49, and the modulus of elasticity is less than 26.33 GPa, the depth of the damage zone exceeds 2 m. Using the weighted least squares method, the influence of each parameter on the stability of the surrounding rock was determined, with uniaxial compressive strength having the greatest impact. Based on this, prediction functions for the maximum displacement of the surrounding rock, stress concentration coefficient, and depth of the damage zone were established. According to the current estimation method, when the deep shaft crosses greisen and potassic granite, the maximum displacement of the surrounding rock may exceed 70 mm, and the depth of the damage zone may reach 5.99 m, making it prone to destabilization and damage.