| With the implementation of China’s “transportation power” strategy,tunnel engineering construction has been vigorously developed,tunnel through the soft broken surrounding rock,excavation disturbance will cause greater surrounding rock deformation,northwest region has many tunnels surrounding rock is mainly collapsible loess and mudstone,in this soft composite surrounding rock area tunnel excavation caused by the complexity of the surrounding rock deformation to tunnel construction has brought great problems,so the tunnel advanced support and excavation method is particularly critical.With the gradual activity and seismic activity in northwest China in the past ten years,the seismic dynamic stability of tunnels in loess area has attracted attention from all parties,so it is of great significance to study the stability of tunnels in loess area under strong earthquakes.Taking the Tongding Expressway Jinping Tunnel as the engineering background,this paper conducts research through literature analysis,on-site monitoring and numerical simulation of the tunnel entrance section,and the main conclusions are as follows:(1)The analysis of the on-site monitoring data of the tunnel entrance section shows that the vault settlement and horizontal convergence of the left and right tunnel openings basically reach stability between 60 and 80 days,and the settlement of the left tunnel entrance section is more significant,while the horizontal convergence of the left tunnel opening section is close to the horizontal convergence of the right line opening.(2)Through numerical simulation,it is found that the single-side wall guide pit method performs relatively well in dealing with the deformation of surrounding rock,the force of the supporting structure,the size and distribution of the plastic zone,so the single-side wall guide pit method is the best excavation method in this project considering the engineering economy.(3)Compared with the deformation of the loess tunnel opening section after excavation using the single-side wall guide pit method under different advanced support conditions,and further comparing and analyzing the support combination of pipe shed support and horizontal rotary spray support with advanced small conduit,it is concluded that the horizontal rotary spray support effect is better when the advanced support is carried out in a single way.The support effect of the two support forms with the advanced small conduit is significantly better than the use of pipe shed support alone or horizontal rotary spray support,and it is more reasonable to choose the horizontal rotary spray support and the support combination of the advanced small conduit for the advanced support of the tunnel opening.(4)The stability of the surrounding rock of the tunnel under four seismic conditions was selected for comparative study,and it was found that the tensile stress and compressive stress at the arches on both sides of the tunnel were large,which was the area where the tunnel was most prone to plastic failure under seismic conditions,and the maximum displacement mainly occurred at the edge of the surrounding rock and the arch waist of the tunnel.Under conventional excavation disturbance,the Z-axis direction of the displacement has the greatest influence,and under the seismic dynamic disturbance,the X-axis direction of the displacement has the greatest influence.Through the deformation and force analysis results of the tunnel under the dynamic load disturbance of 0.2g peak acceleration,it can be seen that the support of the tunnel arch foot and arch waist should be strengthened,and the key monitoring should be carried out. |
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