| Because of its weakness,fracture,looseness,low strength,and poor self-stability,weak surrounding rocks exist as a poor geological condition.In order to ensure that the tunnel safely passes through weak surrounding rocks and the surrounding rocks are in a stable and safe state,we must adopt auxiliary construction methods to pre-support surrounding rocks.As one of the auxiliary construction methods,pipe shed advanced pre-supporting technology has been widely used in China's tunnel engineering due to its advantages of long support distance,good reinforcement effect,short construction period,and economical and reasonable cost.However,at present,the design,construction,research,etc.of the pipe shed cannot yet meet the needs of the project construction.Therefore,this paper uses the Meiyuan Tunnel in Wenzhou City,Zhejiang Province as the engineering background to study the advance technology of pipe shed pre-supporting.The main work is as follows:(1)Analyze and evaluate commonly used advance pre-supporting techniques;Explaining the application and research status of advanced pre-support technology for tube sheds.This technology is an effective method to control the deformation of surrounding rock in soft surrounding rock tunnels.(2)Summarize the meaning,influencing factors and deformation characteristics of weak surrounding rock.At the same time,the composition of the pre-supporting force,the pre-supporting principle and the deformation control method for the weak surrounding rock were analyzed.(3)In-depth analysis of pipe grouting reinforcement mechanism and supporting principles.The commonly used methods for determining the slope stability are analyzed,and the stability evaluation method for the face under the support of the shed is proposed.(4)Considering the pipe roof as an elastic foundation beam,a double-parameter elastic foundation beam model(Pasternak model)was established for the single steel pipe in the tunnel pipe shed structure.The mechanical behavior of the pipe shed was studied and the deflection,rotation angle and internal force equation of the pipe shed were deduced.Matlab programming program was used for calculation and analysis.At the same time,based on the study of the mechanical behavior of pipe sheds,the factors such as the excavation step,the distance between pipe sheds,the diameter,the surrounding rock pressure and the elastic coefficient of soil were optimized.(5)Using the MIDAS GTS NX finite element software,a three-dimensional numerical model of the construction process of the Meiyuan Tunnel was established.Analyze and study the deformation of the tunnel surrounding rock and supporting structure under the condition of whether or not there is tube roof pre-support.Studies have shown that the application of tube shed pre-support structure can effectively control the deformation of surrounding rock and shotcrete structure,and can also reduce the stress.With the tunnel excavation,the tube shed pre-support structure can well transfer the surrounding rock pressure.The settlement curve of the surrounding rock under the pre-support of pipe sheds converged.(6)Analyze and study whether the pipe shed structure is grouted and the thickness of the grouting layer is changed.The influence of working conditions on the deformation of surrounding rock and steel pipe.The research shows that the support effect after pipe grouting is obviously improved and there is a reasonable range of grouting thickness in the pipe shed. |
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