Numerical simulation of slurry fracturing during shield tunnelling

Abstract

The slurry type shield method is an important tunnelling method, especially for underwater tunnels in soft soil. If the slurry pressure is too high, it may lead to slurry fracturing of the stratum in front of the excavation face and cause water inrush accidents. Controlling the face stability of shallow shield tunnels is difficult owing to the inadequate understanding of the slurry induced fracturing mechanism. Most importantly, understanding the details of the slurry fracturing propagation process is not enough, as the process is especially complicated. However, the propagation process cannot be directly observed in the field or in small-scale laboratory tests because it occurs in bodies of soil. Thus far, an effective approach to investigate the slurry fracturing mechanism in the surrounding stratum of a slurry shield tunnel has not been reported. In this paper, a numerical simulation method for evaluating tunnelling-induced slurry fracturing is presented. The developed numerical model considered the couplings of stress distribution, fluid flows, and fracturing. The fracture initiation, branching, and propagation in the stratum could be reproduced numerically. A series of simulations for different ratios of cover depth to tunnel diameter were carried out to investigate the propagation process of slurry fracturing. The effects of slurry pressure at the tunnelling face and the cover depth above the tunnel were investigated. The results of the fracturing process induced by slurry, such as the fracture propagation velocity, slurry pressure distribution along the fracture, fracture initiation pressure, fracture extending pressure, and stratum deformations, were analyzed.