Abstract:

In this paper, a numerical model simulating the process of the failure of the tunnel face in shield tunneling is established on basis of a rivercrossing tunnel in Nanjing, China, and the change of the soil stress and the soil arch effect accompanied by its redistribution is studied. It’s revealed that from the bottom up, as the excavation face’s displacement increases, the vertical stress of the soil decreases before it keeps stable later, while the horizontal stress decreases before it rises slightly. As the tunnel cover becomes smaller, the coefficient of the lateral pressure of the soil increases before it decreases later. When the displacement of the excavation face becomes serious, both the vertical stress and the horizontal stress ahead of the excavation face decrease. Thus the buckling failure zone is formed. The vertical stress of the soil on top of this zone becomes lower, and the horizontal stress of the soil on top of this zone becomes higher, thus the vault area is formed. The vertical stress of the soil around the buckling failure zone becomes higher, and the horizontal stress of the soil around the buckling failure zone becomes lower, thus the arch foot area is formed and the soil arch effect gradually comes into effect.

Key words: shield tunneling, sandy soil strata, tunneling face stability, stress state of soil