Tunneling-induced deep-seated landslides: a case study in Gulin County, Sichuan, China

The excavation of a highway tunnel revived an ancient landslide in Gulin County, Sichuan Province, China, which resulted in many severe problems such as ground surface cracks, tunnel deformation, and supporting structure damage. This paper focused on the interaction between the old landslide and the tunnel. First, the engineering geological conditions and deformation characteristics of the ancient landslide were determined on the base of field geological survey and geological prospecting. Second, the calculation parameters of the sliding body and sliding zone were obtained by back analysis to the surface deformation monitoring data. Finally, the failure mechanism of landslide due to tunnel excavation was discussed by three-dimensional numerical simulation, and the effect of proposed reinforcement measures was evaluated. The investigation results show that the ancient landslide consists mainly of gravel and block stones, and the major reason for the landslide failure is that the tunnel is exactly across the ancient landslide belt. The sliding surface below the left tunnel is gentle, and the thick sliding body prevents the upper body from sliding largely. Therefore, the deformation of the sliding body mainly occurred in the region above the tunnel. The calculated overall deformation range and value for the sliding body by back analysis are in good agreement with the field survey results and slope deformation monitoring data. According to the tunnel construction period and deformation characteristics of the sliding body, it is suggested to remove some part of the sliding body above the tunnel. The numerical simulation results show that, after removal, the sliding body and tunnel are small in deformation and are stable. The research results in this paper not only keep the tunnel under good construction and operation but also ensure the people and their property, which saves much construction cost and provide a valuable reference to similar projects.