| With the rapid development of China’s railway construction,a large number of mountain tunnels have been built in the high intensity and strong earthquake areas in the West.Because of the complex geological conditions in this area,these tunnels are bound to face the test of strong earthquake action.It is of great engineering significance to carry out the stability analysis and anti-seismic technology research of the tunnel portal section in this area.In this paper,the DK213+350～420 mileage section of a tunnel imported from Cheng-LAN railway is taken as the research object.Based on the field geological survey,rock mechanics test and the monitoring data of surrounding rock deformation,based on the detailed analysis of the deformation characteristics and mechanism of the surrounding rock in the tunnel entrance section,the stability of the surrounding rock under static and seismic dynamic conditions is analyzed with the numerical simulation technology.The anti damping performance of the design support measures is studied,and the optimization effect of different anti vibration measures is discussed.Finally,the comprehensive anti damping measures for tunnel entrance section are put forward.The main results are as follows:1)The surrounding rock of the entrance section of the tunnel is mainly sandstone,slate and phyllite.The rock mass structure is broken,and there are three sets of superior joint planes,all of which are type V surrounding rocks.The deformation of surrounding rock in the entrance section of the tunnel is concentrated in the vault and the arch waist.The time effect is mainly characterized by four stages of initial rapid deformation,slow deformation,rapid deformation and convergent deformation,and the time required for the deformation of the surrounding rock to be stable is about 50 days.The main characteristics of the space effect are as follows: the deformation release rate is 50%～70% when 1 times the hole diameter of the palm,and the deformation is basically stable when 2 times the diameter of the palm surface;the surrounding rock is completely stable when the distance from the palm surface is 2.5times the hole diameter.2)The surrounding rock deformation of tunnel entrance section is mainly controlled by surrounding rock structure and rock quality,and its deformation mechanism can be divided into two types: shear slip and plastic flow.Among them,the DK213+350～380 mileage section is affected by structural surface and shallow surface transformation,the deformation of surrounding rock is mainly shear slip.The content of phyllite in tunnel surrounding rock is higher in DK213+380～420 mileage section,and the deformation of surrounding rock is mainly shear slip and plastic flow.3)Under static conditions,the deformation of the tunnel entrance section is mainly located in the vault and the arch,and the rock around the tunnel is subjected to different degrees of compressive stress.Under the earthquake dynamic conditions,the displacement and stress of the tunnel entrance section are obviously enlarged,and the vault is the weakest part of the seismic capacity.The existing design support measures have good seismic performance and can meet the seismic design requirements of the tunnel entrance section.4)By comparing and analyzing the optimization effects of three different anti shock methods,The anti damping effect of strengthening the surrounding rock is the most obvious,the second is the shock absorption layer,and the seismic effect of adjusting the stiffness of the lining is relatively weak.5)According to the optimization effect of different anti shock and damping measures,the comprehensive anti damping measures of "surrounding rock grouting reinforcement with 3 m+ 20 cm damping layer + increase the stiffness of 0.5 times lining" are put forward.This measure can reduce the displacement of the dome with the weakest seismic capacity by 50%,and the stress of the lining structure reverts to the state before the earthquake power is applied. |
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