Analysis On Influence Of Tunnel Excavation On Stability Of Ancient Landslide

The mountainous terrain in China is complex and the traffic facilities are backward,which greatly restricts the development of regional economy.As the country gradually promoted the construction of the western region,infrastructure construction was started on a large scale in the southwestern mountainous areas,and the construction of highway and railway was the key project.When building roads and railways in mountainous areas,it is often necessary to pass through the mountains in the form of tunnels.When the tunnel must cross the ancient landslide in a certain position,the construction of the tunnel has a great threat to the ancient landslide.The influence of tunnel excavation disturbance on the stability of ancient landslide is a key problem that must be considered in construction safety.In actual engineering,the relative position relationship between tunnel and ancient landslide is different.Aiming at the orthogonal system of tunnel-ancient landslide,this paper studies the stability of medieval landslide in tunnel excavation process from the aspects of theoretical analysis,numerical simulation and large indoor direct shear test.Firstly,the existing research on slope stability analysis is summarized,and the research results on the stability of a special geological body—ancient landslide are emphatically introduced.The sliding zone is the key part in the stability analysis of ancient landslides.Therefore,based on the strength reduction method and the characteristics of ancient landslide,the reduction range of double-strength reduction method is optimized.The dynamic local double-strength reduction method,which only reduces the strength parameters of sliding zone soil,is used to analyze the stability of ancient landslide on the platform of FLAC3 D numerical simulation software and Midas/GTS modeling software.Secondly,based on the quadratic regression orthogonal combination test design,the construction method of the maximum displacement formula of sliding zone caused by tunnel excavation is proposed.A series of numerical tests are carried out on the tunnel-ancient landslide orthogonal system by this method,and the sensitivity of several influencing factors is compared.The effectiveness of the method is preliminarily verified by numerical examples and engineering examples.Then,due to the inherent relationship between the strength and deformation of sliding zone soil,using large-scale direct shear test in the laboratory,the pre-shear is used to simulate the displacement of sliding zone caused by tunnel excavation disturbance,and the reduction coefficient of shear strength of sliding zone soil composed of different particles caused by tunnel excavation disturbance is obtained.Finally,combined with an engineering case of a tunnel crossing an ancient landslide in southwest mountainous area,according to field data,the maximum displacement of the sliding zone caused by tunnel excavation is compared between regression equation and FLAC3 D numerical simulation.The strength reduction of the sliding zone soil is analyzed by the indoor large-scale direct shear tests,and the stability of the ancient landslide is analyzed by dynamic local double strength reduction method.The proposed method is validated.