Optimum Analysis Of Parameters Of Shed-pipe Advanced Support In Weak And Fractured Surrounding Rock Tunneling

In tunnel construction,due to the different construction environment and complex geological conditions,construction under adverse geological conditions is often encountered.In order to solve this kind of construction difficulties,advanced support system was born.Common advanced support and reinforcement methods include advanced small pipe,horizontal jet grouting,mechanical pre-cutting groove,pre-lining,advanced pipe shed,etc.As a kind of tunnel support technology,pipe shed advance support is widely used in crossing complex strata because of its advantages of long reinforcement distance,short construction period and high reliability.However,at present,there is no mature theoretical basis for the design and construction of pipe roof,and many of them rely on engineering experience to design,which can not meet the increasing demand of tunnel engineering for construction cost control and safety assurance.Therefore,it is of great practical significance to study the mechanism and parameter selection of pipe roof support in the field of underground engineering.Based on a large number of documents and construction materials,this paper studies the design and construction methods of pipe shed and the mechanical mechanism of pipe shed support.Based on the actual project and using 3DEC numerical simulation software as the research method,the optimization of pipe shed parameters under weak and fractured surrounding rock is systematically studied.The following research has been done:1.Summarize and analyze all kinds of advance pre-support methods,and introduce and analyze the application scope,design parameters and construction methods of pipe shed construction.2.Based on the theory of surrounding rock pressure of shallow-buried tunnel,the mechanical mechanism of pipe-shed support is analyzed,and the results are compared with the actual project.The rationality of the two-parameter elastic foundation beam model is verified.Based on this research method,the differential equations of pipe-shed deflection,rotation angle,bending moment and shear force in the mechanical model of pipe-shed are obtained.The influence of the coefficient of foundation bed and shear modulus on the support of pipe shed is studied,and the relationship between the coefficient of foundation bed and the internal force of pipe shed is obtained.The load transfer capacity of the pipe shed is studied,and the conclusion that the pipe shed mainly plays the role of load transfer in the advance support system is obtained.3.Using 3DEC discrete element software,the supporting effect of pipe roof support model is analyzed,and compared with the actual project to verify the rationality of the model.The influence of pipe shed parameters on supporting effect is studied from the aspects of circumferential spacing,grouting thickness,pipe shed diameter and excavation footage.Based on the actual project,the parameter selection of pipe shed construction is optimized,and the design parameters and optimized parameters are compared,and the influence of pipe shed parameters on support function is further demonstrated.