Critical Instability Criterion of Large-Diameter Shafts in Deep Topsoil Based on Ultimate Strain Analysis

Abstract

Shaft stability plays an important role in mine safety. Most of the previous studies focused on the stress analysis of shafts using monitoring data. Since the shaft wall state in the deep topsoil stratum is still not clear, the ultimate analysis method is adopted to study the bearing capacity and the strain of a large-diameter shaft wall in Yanzhou coal mine. First, the bearing capacity of the shaft wall is discovered. The value of the auxiliary shaft, main shaft and ventilating shaft is 22.22 MPa, 22.07 MPa and 21.73 MPa, respectively. Then, the ultimate strain of the shaft wall is obtained; the designed ultimate strain corresponding to those shafts is 1.468‰, 1.458‰ and 1.435‰, while the working ultimate strain is 2.078‰, 1.800‰ and 2.638‰, respectively. Since the working values are greater than the design values, the shaft walls need to be reinforced, which is consistent with the field situation. Finally, numerical analysis based on the finite difference method (FDM) is performed to investigate the evolution process of ultimate strain on the shaft wall. The results show the ultimate strain could provide a theoretical basis for safe service and management of a large-diameter shaft in a deep topsoil area.