Centrifuge model test and numerical simulation of stability of excavation face of shield tunnel in silty sand

Through centrifugal model tests, the failure characteristics of the shield tunnel excavation face and the limit support pressure in dry and saturated silty sands are studied. By means of remote control of soil displacement, the relationships between the support pressure and the displacement of the excavation face are obtained, and the failure mode of the excavation face to the active limit equilibrium state is revealed. Two sets of dry silty sand centrifuge model test results show that when the ratio of tunnel depth to the tunnel diameter is from 0.5 to 1, the failure mode of the excavation face is changed from the whole collapse to funnel shape, but the change of of the limit support pressure is small. The test in saturated silty sand shows that the destruction extent in the horizontal direction of the excavation face is more than that at the same buried depth in dry sand, and the limit of the support pressure increases significantly. Three-dimensional elastoplastic finite element method is used to simulate the failure process of excavation face, and then the limit support pressure and failure mechanism of the excavation face are obtained. The numerical simulations are in good agreement with the experimental results. Additionally, the influence of the soil strength parameters, tunnel depth and seepage on the limit support pressure is further analyzed through the numerical simulation, it is shown that the damage area and the limit support pressure of the excavation face are larger than that of the nonseepage condition; the limit support pressure decreases with the increase of the internal frictional angle, and decreases with the increase of the tunnel depth.