Physical modeling of wetting-induced collapse of shield tunneling in loess strata

The wetting-induced collapse of loess strata affects tunnel structures and is a key challenge in geotechnical engineering. In this study, we investigated the mechanisms that influence wetting-induced collapse/deformation of loess strata on the lining structure of a subway tunnel. First, a centrifugal field immersion unit and a monitoring system were developed based on the centrifuge working platform. The immersion device was composed of two sub-systems including a water supply system and a diffusion system. Subsequently, centrifugal model tests were performed under different wetting conditions to explore the impact of wetting-induced collapse of loess strata on the structure of the subway tunnel. The testing results showed that the non-uniform subsidence of the tunnel base induced by non-uniform wetting was the major cause of the collapse and deformation of the tunnel structure. The axial bending moment of the tunnel was found to be largest in the middle of the tunnel and decreased toward both ends. In addition, a layer of non-collapsible soil or properly treated collapsible soil with a certain thickness could effectively resist deformation induced by the subsidence of wetted loess. With an improved immersion simulation unit design and measurement device configuration, after being wetted, the pressure arch in the soil strata became weaker and gradually disappeared, resulting in a reduced range of the pressure arch on the side wall of the tunnel and complete elimination of the pressure arch effect on the top of the tunnel.