Soil Arch Effect Analysis of Shield Tunnel in Dry Sandy Ground

Abstract

During shield tunneling, the soil arching effect in front of the excavation face can effectively reduce the impact of excavation on the surrounding environment. This effect was studied with different depth/diameter ratios of the tunnel (1., 2., 3.) as well as different densities of the sand layer (1.5 g/cm3, 1.6 g/cm3, and 1.7 g/cm3). The displacement mode of sand particles, developing characteristics of soil arching near the excavation face and the ground surface settlement were analyzed. Particle flow code was utilized to simulate the process of shield tunnel driving and the soil arch effect was investigated at the microscopic scale comparing with laboratory model tests. The contact forces between particles, porosity and average soil pressure were studied to understand the soil arching effect. Test results showed that the range of the soil failure zone above excavation face depends on the internal friction angle. The range of failure zone for small internal friction angle was a similar wedge. The failure zone was found to be a long strip for the large internal friction angle and the soil arch effect was stronger. After the soil arching effect disappeared, it was found that the wedge was smaller, as was the sliding area over the wedge. The height of the soil arch was greater, while the width of the soil arch was smaller, with a larger internal friction angle. The highest point of the soil arching was located approximately .2–.3 D from the support plate. After analyzing force chain, porosity, supporting force, and so on, this study came to the conclusion that the soil arch effects obtained from the particle flow code agreed with the results of physical model tests.