A DEM-based study of the disturbance in dry sandy ground caused by EPB shield tunneling

Abstract

A discrete element method simulation was used to evaluate tunneling-induced ground movement and the parameters of tunnel boring machines. The process of excavation by an Earth Pressure Balance (EPB) shield machine, including soil excavation with a cutter head, soil conditioning in the chamber, and removal of the excavated soil with a screw conveyor, is modeled using the Discrete Element Method (DEM). Deformation of the surface and subsurface of the ground in a sandy soil were studied for different tunnel burial depths and different screw conveyor rotation speeds with a constant advance rate. In addition, machine parameters, such as the cutter head torque, the normal pressure on the cutter head, the screw conveyor torque, and the chamber pressure also were analyzed. The results of the DEM model were found to be in good agreement with results reported in the literature. The method showed great potential for the analysis of both tunneling-induced ground movement and ground-machine interactions. It was determined that the distribution of the pressure of the soil in the chamber was non-linear, especially near the screw conveyor. The pressure of the soil in the chamber, the torque of the machine, and the normal pressure on the cutter head increased with the depth of excavation until a depth was reached at which stress arching occurred in the soil. Changes in the depth of excavation had little effect on the torque of the screw conveyor.