Numerical Investigation of Slurry Fracturing during Shield Tunneling under a Reservoir

Abstract

The Jinan Jiluo Road Crossing the Yellow River Tunnel North Extension Project will intersect the Queshan reservoir, which currently supplies 60% of the domestic water in Jinan City. During the excavation process of the large-diameter slurry type shield used in this project, it may lead to slurry fracturing of the stratum in front of the excavation face and slurry blow-out from the surface if the slurry support pressure is too high. The leakage of shield slurry will pollute the reservoir water, and the safety of domestic water in Jinan will be threatened. Shield slurry blow-out may also lead to water inrush accidents. It is difficult to prevent slurry blow-out during shallow shield tunnel construction due to an insufficient understanding of the shield slurry fracturing mechanism. The initiation and extension of shield slurry fracturing are very complex and difficult to observe in the stratum. Currently, there is no effective method to study the slurry fracturing mechanism of shield tunneling. This paper presents a numerical simulation method of shield tunneling slurry fracturing based on the extended finite element method (XFEM). The risk of slurry blow-out in shield tunnel crossing reservoir engineering is analyzed. The advantages of the XFEM for simulating crack propagation are fully exploited. Considering the coexistence of tensile and shear failures in soft soils, embedding the combined tensile and shear failure criterion is realized in the XFEM by the secondary development of the ABAQUS extended finite element. Compared with the slurry fracturing test of blind-hole clay samples, the rationality of the simulation method for slurry fracturing in cohesive soil is verified. Through the establishment of the slurry fracturing extension model, the slurry fracturing process of shield tunneling in cohesive soil layer is simulated. The variation law of slurry pressure in the process of fracture extension is studied, and the influence of shield slurry support pressure, overburden thickness, formation shear strength, and slurry viscosity on fracture extension pressure and extension path is analyzed. Based on this numerical simulation method, the risk of slurry blow-out is analyzed in the shield tunneling intersecting the Queshan Reservoir of the Jinan Jiluo Road Crossing the Yellow River Tunnel North Extension Project.