Three-dimensional numerical simulation of slurry fracturing during shield tunnelling

The slurry shield tunnelling is an important construction method which is widely applied in tunnel engineering. This method can lead to slurry fracturing failure to the stratum under complex conditions. However, there is no readily available method which can be used to study the mechanism of slurry fracturing during shield tunnelling. To provide a convenient tool for this issue, a three-dimensional numerical method is developed based on the smeared crack model and the volume of fluid method. It is implemented numerically in our in-house finite element code and then used to simulate a three-dimensional shield tunnel, wherein the morphology and process of the slurry fracturing are simulated. The fracture-induced displacement is investigated. The effects of the soil cohesion, internal friction, modulus and tunnel size on the fracturing are studied. The numerical results indicate that when the fracture propagates till the stratum surface, a trapezoidal block with wide top and narrow bottom can occur in the stratum above the shield machine. This block is found to produce the most part of the upward deformation for the stratum. As compared with the tunnel with relatively small diameter, the large-diameter tunnel has shorter fracturing path toward the stratum surface and provides easier propagation condition for the fracture after occurrence. It is therefore concluded that the safety rick of fracturing is higher in the large-diameter tunnel.