Research On Control Norm Of The Tunnel Deformation In The Loess

The great western development strategy implementation of the decision, and promote the development of the western region of high grade highway, across the highway tunnel loess area will be more and more. Because of, the loess has unique structural and strong water sensitivity,taking JiuZhou tunnel engineering as example, it has buried depth, large span, low strength, large sections, the deformation of the surrounding rock big character, it is difficult to accurately grasp supporting occasion, such as too large deformation lead to cavity collapse and geological disaster, at present,it can be through studied deformation control benchmark to solve the problem.This paper based on the constructing case project of JiuZhou tunnel from the north loop of LanZhou to109national highway section,by using the finite element analysis software MIDAS/GTS to simulate different construction condition of JiuZhou tunnel, extraction the plastic strain and limit displacement value of key points surrounding the tunnel,Through the limit displacement establish management benchmark to guide the loess tunnel construction.This paper introduces the present situation of the the loess tunnel and summarized the Limit displacement control basic value at home and abroad. This paper introduct the Project summary of JiuZhou tunnel and the characteristics of loess engineering and discusses the influence that include internal and external causes that affect the deformation of the loess tunnel. This paper took the theoretical of plastic mutations as guidance, by using finite element analysis software simulation different sections, different construction condition (three benchs seven steps excavation method) of JiuZhou loess tunnel, and got the limit displacement of the loess tunnel when is destroyed. According to the limit displacement value to establish three-level deformation control standards and combine with the actual displacement that correspond the Simulation results to guide the construction. By studying the deformation control standards, draw the law and the conclusion of the loess tunnel:(1) According to the genneral situation of JiuZhou Loess Tunnel, combined with the loess own physicak mechanical properties, and conclude that the reason of the deformation of the loess tunnel. That is surrounding rock characteristics of loess tunnel is the distortion of the internal cause, design method, support the parameter selection and construction method of the deformation of the tunnel external cause, it is precisely because the cause and external cause, under the common function of loess tunnel caused the unique shape.(2) MIDAS/GTS application software simulation calculation JiuZhou tunnel in different conditions (three benchs seven steps excavation method), different buried deep (20m,30m,40m) the limits of the displacement.(3) According to the comparison between the measurements of the displacement and the limit of the displacement value, established three-level management standards in the loess tunnel, got the control benchmark values for deformation of loess tunnel under depths20m,30m,40m.(4) This paper offer the support of loess tunnel method and the general principle, it proposes deformation of JiuZhou loess tunnel surropt and measures which played a role to improve the safety of the loess tunnel construction.