Research On Safety Measures For The Shallow Exit Section Of Qifengshan Unsymmetrical Pressure Double-arch Tunnel

In the process of mountain tunnel construction,the tunnel is the key control project of the whole line,and the safety construction at the portal is the key problem in the construction of the tunnel project.The exit and entrance of the eccentric arch tunnel are often in the bad geological section,such as shallow buried,partial pressure,high weathering degree,rock breaking and so on.In addition,the existence of side slope makes the force more complicated after the tunnel excavation.When excavation and entry of tunnels are excavated,there are often large deformation of surrounding rock,initial deformation and two lining cracks.Serious accidents may lead to collapse and instability.In this paper,taking the shallow buried exit section of Fengshan eccentric arch tunnel as the research object,this paper adopts the methods of theoretical analysis,numerical calculation,field monitoring and engineering verification to carry out the research on the safe disposal measures of shallow buried exit section of Fengshan partial pressure continuous arch tunnel.The main contents are as follows:(1)Through consulting literature and site geological survey,the causes of bias tunnel are determined.On this basis,based on the case,specification and prune theory of relevant tunnel engineering,the critical depth of the buried depth of a partial pressure tunnel under different slope and buried depth is calculated.(2)According to the relevant specifications,combined with the tunnel geological conditions and construction method,the horizontal and vertical pressure of the tunnel under eccentric load is calculated by the formula.According to the calculation results,the relationship between the pressure parameters of the multi arch tunnel under different bias angles and different burial depths is studied.(3)The topographic and geological conditions of the tunnel entrance section of bimonthly road are counted from the aspects of slope slope,horizontal slope,buried depth of tunnel,bad geology and the grade of tunnel surrounding rock.According to the statistical results,the situation of tunnel entrance is classified.(4)According to the results of the above statistical classification,the effects ofdifferent working conditions on the excavation deformation of tunnel with different transverse gradient and different side overlying soil are established by using the numerical simulation software,and the measures need to be taken.Based on the simulation results,the location and scope of safety measures need to be taken into account.(5)According to the simulation and statistical results,the FLAC3 D is used to simulate the situation that needs to be taken,and the effect of the safety disposal measures before and after the simulation are compared.Finally,the safety disposal measures are verified by the method of monitoring the actual engineering monitoring.