Study On The Stability And Supporting Measuresof Double Arch Tunnel Door In Landslide Zone

When the tunnel is built in the landslide zone,the geological conditions of the side slope of the mouth of the tunnel section are usually complicated,and the supporting measures are a little improper,which will easily cause the slope deformation,collapse and other geological disasters.In addition,the portal is not only one of the important parts of the tunnel structure,but also relates to the safety of the construction of the tunnel,and affects the later normal operation.In view of the above situation,this paper mainly makes the following contents:1.Based on the limit equilibrium theory,this paper analyzes the stability state of the slope at the mouth of the tunnel under the support of the original retaining wall in the south district road before the excavation of the tunnel,and calculates the internal force and displacement of the retaining wall.Tunnel excavation damaged the structure of the original retaining wall,which can no longer be regarded as a pile and plate retaining wall to check its stability.In this paper,it is regarded as the end wall tunnel door,and the strength limit state of the tunnel door is analyzed.It is found that if no reinforcement measures are taken,the tunnel door will be unstable.On this basis,two supporting measures are adopted to reinforce the tunnel door,that is,anti-slide pile support and anti-slide pile plus inclined support.Through calculation,it is found that if a single row of anti-slide piles is used to support the tunnel door,the deformation of the anti-slide piles is large,and the lateral wall pressure is greater than the lateral allowable compressive stress of the foundation,the landslide thrust should be transmitted to the front pile and the back pile respectively through the inclined support.2.The finite element software MIDAS/GTS NX was used to simulate the stability of the tunnel door during the tunnel construction under the support of anti-slide pile and inclined brace.It is found that the support effect of anti-slide pile can be improved by transferring the landslide thrust to the front pile and the back pile respectively by means of the inclined brace,and the internal force and displacement of the support structure are within the allowable range in the construction stage.In addition,the prestressed anchor cable can restrain the deformation of anti-slide pile and improve its stress.In this paper,one row of prestressed anchor cables and two rows of prestressed anchor cables are respectively applied to the anti-slide piles to reinforce them,and it is found that the prestressed anchor cables can significantly improve the stress of tunnel doors,but have little influence on the deformation of surrounding rocks.Therefore,this paper analyzes the existence of the pipe shed,the influence of the horizontal displacement and vertical displacement of the surrounding rock in the tunnel construction process,and concludes the importance and necessity of the pipe shed and other advanced support.3.During the construction process,the deformation of the slope and the surface,the settlement and horizontal convergence of the tunnel vault were monitored dynamically.Analyze the monitoring data,predict the deformation trend of the surrounding rock,and judge the stability of the slope.By comparing the monitoring results with the numerical simulation results,it is found that although there are differences between the two in the numerical value,they have the same trend of change.The necessity of site monitoring is discussed to provide reference for similar projects.