Asymmetric instability damage patterns of curved shield tunnels based on transparent soil visualization model tests

Abstract

With accelerated urbanization, underground structures have imposed significant restrictions on underground spaces. Urban shield tunnels must be designed using curved lines to avoid existing tunnels, pile foundations, and other structures. Over-excavation on the inner side of a curved tunnel during tunneling and the difference between the inner and outer jacking forces complicate research on excavation surface stability. In this study, a combination of transparent soil visualization model tests and numerical simulation methods was used to investigate the spatially asymmetric distribution patterns, focusing on the progressive destabilization damage of the soil and the soil arching effect in front of the excavation during construction of curved shield tunnels. Furthermore, the effect of the radius of curvature on the soil arch morphology in sandy soils was analyzed in detail. The results show that the soil displacement in front of the working face of the curved tunnel exhibited a crescent-shaped deflection toward the over-excavation side. The settlement tanks in the curved tunnel exhibited an asymmetric distribution along the center of the tunnel and were deflected to the over-excavation side. The smaller the radius of curvature, the greater was the deflection of the soil in front of the curved tunnel to the over-excavation side.