Research On Mechanism Of Pipe Roof Advanced Support For Shallow Overburden Tunnel In Weak Stratum

With the rapid development of economy in China, the high-speed railway, highway and urban subway have entered into a period of rapid development. During the construction of these infrastructure projects, we often encounter the case of tunnel excavation in weak stratum. The weak surrounding rock is not only low intensity, but also vulnerable to the disturbance of tunnel excavation. Thus, rock and soil mass around the tunnel require advanced support before the first formal tunnelling. Pipe roof, as a reliable advanced support method, has been widely used in engineering. In sharp contrast, the theoretical research still lags behind the actual application of pipe roof, resulting in a strange phenomenon, which parameter value still need to be taken by engineering analogy method when designing the pipe roof. In view of these situation discussed above, we researched on the mechanism of pipe roof advanced support for shallow overburden tunnel in weak stratum on the basis of HuaPiLing tunnel engineering in this article. The main work done in this paper as follows:(1) To summarize the advanced support methods which have been widely applied in engineering, analyzing their advantages and disadvantages, and the majority of the studies focus on the summary and analysis about the working mechanism, application areas, development and classification in the mechanical model of pipe roof.(2) Aiming at the defects existing in the pipe roof mechanical model, initial support of delay, surrounding rock stress release time difference, formation reaction coefficient of non-uniformity and the factors such as gradient of up-slope should be considered. The pipe roof is divided into the initial supporting period is closed, primary support is not closed section, not support section, constraints in front of the plastic disturbance period, elastic turbulence period and undisturbed. Established based on the elastic foundation beam theory and considering the construction process of pipe roof deformation mechanics model(Winkler, Pasternak), the theoretical value of pipe roof deformation is deduced. Beam54 in ANSYS was used for numerical simulation of deflection of single pipe roof. Mechanical model proved to be reasonable by comparing the numerical solution and theoretical solution. According to the improved Winkler mechanical model to analysis the parameters including length, diameter, spacing as well as the length of the pipe roof. Based on the improved Pasternak mechanical model to analyze the parameters under different circumstances surrounding rock and surrounding rock slope rate about the pipe roof. Researched the theory of pipe roof in shallow overburden, and provide the reference for the parameter design of pipe roof.(3) Optimized design of the method on detecting pipe roof deflection, using the horizontal inclinometer to monitor deflection of pipe roof. Collected the dates in the field, then a comparative analysis of theoretical solutions and numerical solutions was done, further confirmed the rationality of improved mechanical model.