Physical model test study on steady state effect of underpass tunnel excavation on loose deposit slope

The spatial distribution characteristics of tunnel and loose dump slope，the structural characteristics of slope rock mass，the excavation procedure of tunnel，and other influencing factors are directly related to the cooperative sta⁃ bility characteristics of tunnel and loose dump slope. In this paper，the deformation mechanism of the loose dump slope affected by tunneling disturbance is explored by a physical model test in a waste dump in Shenzhen. Firstly，the opti⁃ mal similarity ratio is determined based on the actual geometric characteristics and spatial distribution characteristics of tunnel and loose dump slope，and the physical model of overlying loose dump body slope is constructed. Then，under the condition of rainfall，a comparison of physical model experiments is conducted for the large⁃span tunnel ex⁃ cavation with two kinds of the working condition of under⁃excavation and without excavation. By analyzing the slope body internal moisture content，pore water pressure，and earth pressure under the conditions of rainfall，the deforma⁃ tion mechanism of the slope instability caused by excavating large⁃span tunnel under loose dump slope with the condi⁃ tion of rainfall. Finally， using the constant resistance and large deformation anchor cable with negative Poisson ratio，the control measures of the NPR (Negative poisson’s ratio) anchor cable in the surrounding rock of the large⁃ span tunnel are proposed，and the control effect is verified by numerical simulation. The results show that after a cer⁃ tain rainfall duration，the failure of the loose dump slope extends from surface to deep，and the main deformation mode is erosion gully. When the slope gully cut area overlaps with the tunnel loose circle，water gushing and local collapse are easy to occur in the tunnel，and then the local collapse of the overlying slope is induced. The NPR anchor cable is used to compensate for the high preload stress of the surrounding rock of the underpass tunnel，and the subsidence of the tunnel vault and the deformation of the overlying slope are effectively controlled，which provides a new idea for the design of tunnel support and slope reinforcement schemes with a similar engineering background.