Dynamic Response Laws And Shock Absorption Measures Of Shallow-Buried Small Distance Tunnel With Asymmetrical Pressure

The shallow-buried tunnel with a small distance is a new type of tunnel structure between the separated tunnel and the multi-arch tunnel.The tunnel can be significantly adapted to the unique geological,terrain conditions and route control.The tunnel helps to the overall alignment planning and optimization of the highway(railway),and has significant economic,social and environmental effects.In the construction of tunnel engineering,it is usually limited by objective conditions such as geological structure,environmental conditions and engineering cost,which inevitably leads to the situation of shallow-bias.In recent years,many earthquake disasters happened all over the world,which has caused significant damage to the underground structure.The seismic resistance became more and more important for the tunnel.At present,the existing researche on the seismic response of the tunnel is not enough and deep enough.Therefore,acceleration and strain response laws of the tunnel,and the variation rule of Fourier spectrum and main frequency are studied.Effective measures for shock absorption are put forward.The study has important practical significance for the site selection,design,and construction of the tunnel.Based on the natural science foundation project:seismic catastrophe behavior and seismic performance evaluation of rock slope with underground cavern(group)(number:51204215).A series of large shaking table tests for shallow-buried small distance tunnel with asymmetrical pressure were designed and carried out.Based on MIDAS-NX finite element software,the seismic numerical calculation model of shallow-buried small distance tunnel with asymmetrical pressure was established.The three-dimensional numerical model was verified by shaking table test.The shear response of tunnel lining under different slope angles,clear distance,loading modes and surrounding rock types was performed.The shock absorption measures of the tunnel were performed.The main contents and conclusions are as follows:(1)Experimental study on shallow-buried small distance tunnel with asymmetrical pressure shaking table.In the horizontal direction,the acceleration response of the lining left half arch are intense.In the vertical direction,the response of the vault and the arch is intense.Compared with the horizontal direction,the acceleration response of the tunnel is more intense in the vertical direction.The thickness of overlying rock,middle rock column,and the rock slope has a significant effect on the trend of acceleration response.The tension strain is less affected by the type of loading wave,while the peak value of acceleration induced by loading wave is more obvious.The tension strains increases with the peak value of earthquake wave acceleration.Generally,the tension strain is larger in the arch and vault.Tension strain of the lining measuring point is greater than the compressive strain.The strain response of anchor increases with the peak value of earthquake wave acceleration,and the residual strain has the exect same rule.(2)Numerical simulation studies on shallow-buried small distance tunnel with asymmetrical pressure shaking table.Under different slope angle conditions,the variation trend of the tunnel shear force is similar,however,the shear strength is different.With the increase of slope inclination,the difference of shear force between the two shoulders of the left hole is larger,while the difference between the two shears of the right hole decreases.The effect of the existing slope on the dynamic response of the tunnel is significant,and the degree of influence is different under different inclination conditions.The shear force at the arch shoulder and the arch foot is larger,but the shear force at the vault is smaller.Under the conditions of 1.5D and 2.0D,the shear response of the tunnel cross section is stronger,while the response of 1.0D and 3.0D is relatively weak.The shear response value of the tunnel cross section is influenced by the peak value of the loading wave.The larger the peak load,the greater the shear response.The linear variation is presented.Under the condition of 30 degree slope,the shear force of the cross section of the small distance tunnel shows a nonlinear trend.Different loading modes have a significant effect on the shear response of the tunnel.Under the same loading mode,different loading directions also have a significant effect on the shear response.The maximum shear force occurs at the arch and arch of the tunnel.(3)Shock absorption measures of shallow-buried small distance tunnel with asymmetrical pressure.The shock absorbing layer can absorb the energy of the seismic wave very well,decrease the damage of the earthquake to the tunnel,and reduce the axial force of the tunnel.By comparing the shock absorbing layers of different thickness,the 10cm thick damping layer is better.The installation of anti-seismic joint device at the tunnel connection can effectively reduce the axial force,shear force,maximum principal stress and minimum principal stress of the tunnel.It is well known that the aseismic joint is a good damping measure.The internal force of a tunnel is lower thanthat of a tunnel without shock absorption.The effect of shock absorption is absorbing layer + aseismatic joint>shock absorbing layer>aseismatic joint.Different damping measures can change the trend of the axial force of the tunnel,and the different damping measures correspond to the different trend of the axial force change.Under the joint action of the shock absorbing layer+the aseismatic joint,it mainly embodies the damping characteristic of the shock absorbing layer.