Study On The Mechanical Response Of Shallow Buried Tunnel Under The Influence Of Construction Method And Vehicle Load

With the frequent occurrence of highway tunnels in the field of highway engineering construction,it is particularly important to study the stability of surrounding rock of shallow buried highway tunnels.Based on the shallow buried construction section of Taishan Tunnel,this paper analyzes the initial surface settlement,arch displacement and surrounding rock stress caused by tunnel excavation by using FLAC^3D software.The analysis shows that the effect of different excavation methods on tunnel excavation is obtained.Sorted from small to large:full-section method,two-step method,three-step method.When simulating three-step excavation,the tunnel vault settlement and surface settlement are the smallest,and the maximum and minimum principal stress values are the smallest.When full-section excavation is adopted,the tunnel vault settlement and surface settlement are the largest,and the maximum and minimum principal stresses are the largest.The timely application of initial support after excavation can effectively improve the stability of the tunnel,and the deformation of surrounding rock and surface settlement are reduced.At the same time,after the initial support of the tunnel,the vehicle load on the shallow buried section above the tunnel is also an important factor affecting the stability of the shallow tunnel.The vehicle load is equivalent to a sine wave function,and the numerical simulation is used to simulate the vehicle load.The three factors of driving speed and vehicle loading times influence the mechanical response of the tunnel,and the depth of influence of the three factors is discussed.Through the dynamic analysis of the vehicle load,the results show that as the vehicle load increases,the displacement of the road surface to the undercut tunnel vault becomes larger,and the effect of the vehicle is larger,which affects the depth increase and the scope is wider.As the vehicle speed increases,the surface settlement increases,but the action time is shorter and the impact on the road surface is smaller.As the number of vehicle loading increases,the displacement and stress response of the tunnel-stratigraphic system are more obvious.It shows that the surface settlement and the tunnel vault settlement become larger,the depth and width of the vehicle load increase,and the maximum and minimum principal stresses increase.Combined with the simulation of different construction methods and the results of the application of vehicle load,in the early stage of tunnel construction,the deformation is small when using the three-step method,which can improve the safety of tunnel construction.After initial support,the number of vehicle loads is the main factor affecting the stability of the ground to the lower tunnel,followed by the vehicle load size and vehicle travel speed.