# Numerical Investigation of Slurry Fracturing during Shield Tunneling under a Reservoir
## 4 Model Setup and Analysis of the Project  
### General Project Information and Engineering Conditions  
The slurry shield tunnel crossing Queshan Reservoir in this study is designed and constructed for road and subway traffic, which is a sub-project of the Jiluo Road Crossing the Yellow River Tunnel North Extension Project in Jinan, Shandong Province, China. Two slurry-type shield machines are used for the construction of the double-track tunnels, and the distance between the tunnels is about 18 m. The diameter of the shield cutter head used in the project is 15.76 m. After the shield starts to excavate, it will start to cross Queshan Reservoir after excavating about 150 m. The length of the underwater section of the shield tunnel crossing Queshan Reservoir is 1550 m. The buried depth of the shield tunnel in the reservoir area is 13.2 m to 24.5 m. The plan view of the project is provided in Figure 13.  
Figure 12: Comparison of simulated values and tests of slurry fracturing pressure under different slurry viscosities [17].  
Figure 13: Plan view of the project.  
Queshan Reservoir is located on the north bank of the Yellow River in Tianqiao District, Jinan City. At present, Queshan Reservoir supplies 60% of the domestic water in the urban area of Jinan, and it is a national first-class water source protection area. The reservoir has been in operation since 2000. Before the reservoir was built, the area was village and farmland. After the residents were relocated, the ground in the area was compacted and a thicker clay layer was laid. According to the geological survey report, the strata for shield tunnel construction in the reservoir area are mainly clay and silty clay. The elevation of the surrounding dam crest of the reservoir is between 31.80 and 33.50 m, which is about 6-8 m higher than the surrounding ground. The highest water level of the reservoir is 30.40 m, which is about 6 m higher than the surrounding ground.  
The diameter of the shield used in this project is large, and the risk of shield slurry blow-out is high when crossing the reservoir. According to the experience of the construction unit in the shield tunnel crossing the Yellow River, the existing technology can basically avoid the instability of the excavation face of the deep-buried shield tunnel under the condition of slurry blow-out. However, avoiding the occurrence of shield slurry blow-out is extremely difficult. Small-scale shield slurry blow-out occurred in the shield tunnel crossing the Yellow River near the project site. However, the massive leakage of shield slurry caused by slurry blow-out will pollute the drinking water of the reservoir. The shield slurry blow-out will also damage the seepage-resistant formation at the bottom of the reservoir and increase the leakage rate of the reservoir. Therefore, the risk caused by the shield slurry fracturing in this project is highly concerning to society. The stratum above the bottom of the shield tunnel in this area is mainly cohesive soil, which is more prone to slurry fracturing. In this section, the XFEM method is used to analyze the slurry fracturing phenomenon of the shield tunneling crossing the reservoir.