Objective Dolomite strata contain numerous concealed karst caves, which easily lead to collapse and water inrush. To ensure construction safety, it is necessary to study the dynamic mechanics variation characteristics of metro shield construction in dolomite strata based on karst cave distribution, and analyze their influence during shield construction.

Method Using the interval between Zaojiaojing Station and Taiciqiao Station on Guiyang Metro Line 3 as the engineering case, a three-dimensional discrete-continuous refined numerical model of a shield tunnel is established by coupling the PFC^3D6.0 discrete element software with the FLAC^3D6.0 finite difference software, aiming to investigate the influence of different karst cave distributions on shield tunnel construction. First, the muck in the shield machine soil chamber is modeled using a rolling-resistance contact constitutive relation, and its corresponding mesoscopic parameters are determined through numerical verification. Second, the deformation patterns of the stratum during shield construction are analyzed, and the mechanical distribution characteristics of the cutterhead torque, thrust, and chamber pressure are obtained. Finally, the dynamic mechanical variation characteristics of shield tunnel construction under different horizontal spacings and spatial distributions of karst caves are further examined.

Result & Conclusion  Due to the influence of the cutterhead cutting direction on land subsidence, shield construction has a significant effect on the soil within 5 meters ahead of the excavation face. The maximum land subsidence occurs on the side closer to the karst cave. When the karst cave is located beneath the excavation face, the shield machine is at risk of nose-diving under its self-weight.