# Numerical Investigation of Slurry Fracturing during Shield Tunneling under a Reservoir
## 1 Introduction
studied the fracture initiation through slurry fracturing laboratory tests of hollow cylindrical clay samples, and proposed some calculation methods to describe the initiation pressure of clay bodies [13, 14, 15]. [PERSON] et al. believed that under the action of slurry pressure, both shear and tensile failure may cause formation fracturing, which largely depends on the properties of soil [16]. Clay strata are more prone to slurry fracturing than sand strata. [PERSON] et al. analyzed the influence of soil strength and slurry viscosity on the fracturing pressure through the triaxial slurry fracturing test of blind-hole specimens [17]. In the current research results, the initiation pressure of slurry fracturing is studied through the mechanical test of geotechnical samples. However, these tests cannot explore the extension process of slurry fracturing in shield tunneling. In order to study the extension process of slurry fracturing in shield tunneling, [PERSON] and [PERSON] et al. observed the extension of slurry fracturing through the shield model test and field slurry fracturing test, respectively [6, 12]. The characteristic laws of the slurry fracturing extension pressure and the extension shape of the split fracture are obtained. Due to the size limitation in the model test of slurry fracturing in shield tunneling, it is difficult to fully capture the occurrence and development process of slurry fracturing. In the field, slurry fracturing tests are observed by manual excavation; the observation process may cause some disturbance to the fracturing surface and implementation is extremely difficult. [PERSON] et al. established a simplified theoretical model to study the slurry fracturing of shield tunneling [18]. The establishment of the theory is based on a summary of existing experimental laws, and the extension details of shield slurry fracturing are simplified to a certain extent. The phenomenon of shield slurry fracturing occurs in the formation and has strong concealment; it is difficult to directly observe the specific fracturing process. In the influence scope of shield tunnel construction, the stratum mechanics state at the location where slurry fracturing occurs is very complicated. At the same time, it is very important to study the slurry fracturing extension to prevent slurry blow-out in shield tunneling. At present, there is no effective method to study the shield slurry fracturing extension process; therefore, a numerical method was adopted in this paper. Shield slurry fracturing is a hydraulic cracking phenomenon in soft soil, caused by shield tunnel excavation. In terms of physical mechanism and mechanical behavior, shield slurry fracturing is highly similar to hydraulic fracturing. The key to studying them lies in how to describe the propagation process of the crack tip. At present, there are many research methods on crack propagation [19; 20]. A large part of the research results of fracture extension are carried out under the background of hydraulic fracturing. Hydraulic fracturing is a widely used stimulation measure for oil and gas wells, and has quickly become a hot spot in computational mechanics with the \"shale gas revolution\" in the United States. Hydraulic fracturing is often used in rock formations to increase production. Fracture mechanics theory is usually used to analyze the hydraulic fracturing behavior of rock, a brittle material [21; 22]. The failure of soft soil is generally shear failure. Although there are some differences between hydraulic fracturing in rock and soft soil, the existing related research can also provide some reference in numerical simulation analysis methods. With the development of computing technology, numerical analysis has become a powerful tool for the study of hydraulic fracturing. Although hydraulic fracturing simulation in rock and soil mass is a very difficult problem, there are many numerical methods for hydraulic fracturing simulation due to high attention.