Soil arching evolution caused by shield tunneling in deep saturated ground

Abstract

Shield tunneling is accompanied by variations of stress and displacement in soil, which could induce the soil arching effect. Although there have been many studies on the soil arching effect caused by shield tunneling, the research on deep-buried and saturated conditions is still lacking. In this study, a finite element model was firstly built and verified by field data. Then, two hypothetical finite element models were established with two different strata to investigate the stress transfer mechanisms, the development law of excess pore water pressure, and the soil arching evolution of deep-buried tunnel. The methods to determine the arch zone and loosened zone were proposed and verified, which were adopted to compare the differences of soil arching effect between saturated sandy and clayey soil layers. The results show that the heights of the arch zone and loosened zone in the saturated sandy soil layer are both higher than those in the saturated clayey soil layer after the shield tunneling. The subsequent strata consolidation resulted in a 36% reduction in the arch zone height in clayey soil, which means that time effect for the soil arching is significant. Compared with Terzaghi's loosening earth pressure theory, in deep ground, the theoretical overburden pressure is only 5.0% larger than the numerical results for sandy soil but 18.3% less than that for clayey soil. The numerical results can bring new sights about the soil arching evolution caused by shield tunneling and the corresponding tunnel overburden pressure in deep saturated ground.