Study of Asymmetric Failure Patterns for Curved Tunnels Using Visualized Transparent Soil Tests

ABSTRACT With increasing urbanization, many of the current structures in the underground severely limited the space below ground. Shield tunnels need to be built in curved lines to bypass already established tunnels, pilings, and other buildings. Considering that a curve tunnel is overexcavated on the inner side (overexcavated side) during the excavation process and the difference in the jacking forces on the inside and outside of the tunnel, the study of the curved tunnel working face stability is more complicated. In this paper, a curved tunnel excavation model is designed independently, and the visualized transparent soil model test of the curved tunnel is carried out by combining with particle image velocimetry software to investigate the soil progressive damage process during curved tunnel excavation. On basis of designed modeling tests, a three-dimensional asymmetric spatial pattern of the soil arch was further given by using the numerical simulation method, and a detailed analysis of the internal friction angle and the curvature radius on the arch effect of sandy soil was performed. It is indicated that the soil ahead of the curved tunnel shows the shape of a crescent in the cross section, which is offset toward the inner side, and a bubble shape in the longitudinal section. In addition, the maximum value of the settlement tank during tunneling is located on the inner side of the curved tunnel, and there is an asymmetric distribution of the settlement curve along the central axis. The soil ahead of the curved tunnel’s working face will have an increased offset to the inside.