The Excavation Method And Asymmetric Support Of The Shallow Buried Bias Neighborhood Tunnel

During the construction of the highway tunnel,the geological conditions of the entrance section of the neighborhood tunnel are generally poor,the improper excavation and support methods will cause great deformation of surrounding rock,and may even cause the rock mass at the top of the tunnel to slide down,thus causing damage to the tunnel.Therefore,it is of great practical significance to study the excavation method and asymmetric support of the shallow buried bias neighborhood tunnel.Based on this,taking the Naban Tunnel of Silan Expressway as the engineering background,This paper takes the Silan Expressway Naban Tunnel as the engineering background,and uses Midas GTS NX finite element software to study the influence of different construction methods,excavation sequences and asymmetric support forms on the stability of the surrounding rock of shallow-buried,unsymmetrical,and small-distance tunnels.Analyze and select the best excavation method and asymmetric support form.The main research contents and conclusions are as follows:(1)According to the engineering geological conditions of the shallow buried bias area of the neighborhood tunnel,combined with the finite element theory,this paper establishes a two-dimensional plane model of its typical section.At the same time,the step method,the core method of the ring excavation and the double-sided pilot pit method are utilized to simulate the excavation analysis,and the changes of displacement,surface settlement,stress and plastic strain of tunnel surrounding rock under different excavation methods are compared.According to the factors that maintain the stability of surrounding rock,this paper concludes that the double-sided pilot pit method is the best excavation method for the shallow buried bias neighboring tunnel.(2)In this paper,the displacement of surrounding rock,surface subsidence,stress and plastic zone range under different excavation sequence are studied.Considering the factors that control the maximum deformation and stress of the surrounding rock of the tunnel,the excavation sequence of the deep-buried side chamber as the advance tunnel should be adopted.However,considering the influence of different excavation sequences on the stability of the middle rock,the reasonable excavation sequence is to use the shallow-buried cavern as the first cave(3)In this paper,the modeling and calculation of asymmetric support for the left and right sides of the single tunnel and the left and right tunnels are carried out by changing the supporting parameters of spraycrete and anchor rod.The results indicate that the asymmetric support of the tunnel is beneficial to reduce the asymmetry of the supporting structure and the maximum plastic strain of the surrounding rock;whether it is to change the supporting parameters of the shotcrete or the bolt,the stability of the surrounding rock of the tunnel Considering the force of the supporting structure,the asymmetric support of the left and right tunnels of the tunnel is better than the asymmetric support of the left and right sides of a single tunnel.