Research On The Construction Technology Of Portal Section Of Mountain Tunnel With Unsymmetrical Loadings

With the development of economy,the demand for convenience and rapidity of traffic is significantly improved.As the key channel of the highway and railway,the construction technology of tunnel directly affects the safety of tunnel construction and operation.The terrain conditions of tunnel portal are complex and changeable,and there are many security problems.Therefore,the research of how to ensure the safe of construction under this complex topographic and geological condition in the tunnel,it becomes very imperative.This article takes the tunnel of Shi Modong at the high speed of Yanji to Changchun as the engineering background,aiming at the topographic conditions such as shallow buried bias in the fracture zone of tunnel portal,study on the stability of surrounding rock using the double sides heading method,applying monitoring and measuring technology and finite element numerical simulation analysis,the criteria for the stability of the surrounding rock and the early warning mechanism of tunnel construction are put forward,providing guidance for the safe construction of tunnel portal.(1)According to the existing theoretical basis,the characteristics of shallow buried bias tunnel and their influence on the construction of portal section are analyzed,and the applicable conditions and effects of commonly used auxiliary construction methods and excavation methods are summarized.Through the study on engineering difficulties of the shallow buried bias,rock crushing,auxiliary construction complex and highly quality control requirements,determined the method of the double sides heading method,and identify the key points of construction control work.(2)Through the tunnel of Shi Modong construction monitoring data by regression analysis to determine the logarithmic function is the optimal fitting equation of monitoring data,and combined with the data analysis of tunnel surrounding rock deformation regularity of excavation in the face,inferring the final deformation and stability time of surrounding rock,providing an important reference for the secondary lining construction.The stability criterion of Shi Modong tunnel surrounding rock is proposed,the early warning standard of tunnel is formulated,the corresponding warning index is established,and a certain system of early warning mechanism is established.(3)Using MIDAS GTS software to simulate the tunnel excavation process,the stress distribution and deformation rules of surrounding rock and supporting system are analyzed,which provides an important basis for judging the stability of surrounding rock,and provides a scientific reference for monitoring and measuring scheme of tunnel.Based on the numerical simulation of Shi Modong tunnel construction process analysis and monitoring results,numerical simulation results and monitoring data shows that the numerical simulation can be very closed and the numerical simulation can objectively reflect the state of the tunnel excavation.The simulation results are true and reliable,and the numerical simulation results can be used to guide the construction of the engineering.