Study On Mechanism And Supporting Characteristic Of Feet-lock Pipe In Loess Tunnel

Feet-lock pipe is an important means to control the deformation of tunnel,it has been widely used in loess tunnel construction.In order to know the mechanism and supporting characteristic of feet- lock pipe in loess tunnel, this paper summarize the existing research results to analysis the mechanism and study the supporting characteristics through numerical simulation analysis method.Besides,the construction technology and the main points of construction of the feet- lock pipe in loess tunnel also have been given.The main conclusions are as follows:⑴Combined the impact of geological characteristics of loess to rock bolt and the mechanism of rock bolt in loess tunnel to study the load distribution and mechanism of feet- lock pipe.Feet-lock pipe can improve the supporting effect by link the initial support and surrounding rock into overall and strengthen the surrounding rock to increase loess’ s self stability,so as to give full play to the role of the initial support.⑵According to the numerical simulation analysis about vertical bearing capacity of different conditions feet- lock(anchor pipe’s length range from 3m to 5m, inserting down angle of feet- lock pipe is between10° and 30°,the pipe’s diameter is 42.5mm and 89.0mm) shows that, improve feet-lock pipe’s length,inserting down angle of feet-lock pipe and the diameter can improve the supporting capacity,reduce soil deformation and plastic strain soil.⑶According to the excavation and support method of Wang Jiagou tunnel,numerical simulation analysis about Wang Jiagou tunnel with different condition feet- lock pipe found that:improve the lock foot anchor pipe ’s length can obviously improve the effect of control the surrounding rock’s deformation,increase the feet-lock pipe inserting down angle can control the vertical displacement better, smaller angle feet- lock pipe is helpful to control the tunnel‘s horizontal convergence,improve it’s diameter has a certain improving effect on the supporting effect,but not significant. Due to the vertical load that initial supporting pass to feet- lock pipe is mostly support by the anchor pipe on the up step and considering the construction factors,this paper suggest that the up step in the loess tunnel should use design parameters θ=30°,l=5m,D=42.5mm,other location should use the parameters θ=10°,l=5m,D=42.5mm,and four pipes in each group.⑷The construction of feet-lock pipe in loess tunnel should be strictly carried out in accordance with the design scheme,based on the special geological conditions in loess tunnel, the pipe need to construct in dry method.And should control the grouting and welding quality well,so as to ensure its bearing capacity can give full play to.