Study On The Effects Of Different Shock-Absorbing Measures In Shallow-Buried Unsymmetrical Tunnels

With the development of my country’s infrastructure construction,a large number of highway tunnels have been built in recent years.Due to the influence of topography,geology and construction conditions,the tunnel is prone to shallow buried bias.Shallow-buried,unsymmetrical pressure tunnels have the characteristics of poor integrity and uneven surrounding rock pressure.Therefore,shallow-buried,biased tunnels in areas susceptible to earthquakes are more susceptible to earthquake damage than ordinary tunnels.At present,there are few researches on the dynamic response of shallow-buried and unsymmetrical tunnels and damping measures.Therefore,studying the dynamic response law of shallow-buried unsymmetrical tunnels and adopting effective damping measures for damping are of great significance to the design of such tunnels.This subject was funded by the Hunan Provincial Natural Science Foundation project "Seismic response characteristics and damping mechanism of foam concrete damping layer in shallow-buried unsymmetrical tunnels".Using the method of combining model test and numerical simulation,the seismic response law of shallow-buried and unsymmetrical tunnels,the damping effect of the damping layer and the damping effect of ring steel plates in the tunnel boundary are studied.A method combining model test and numerical simulation is used.The seismic response law of shallow-buried unsymmetrical tunnels is studied.The damping effect of the damping layer is studied.The shock absorption effect of ring-shaped steel plates in the tunnel boundary is studied.The research carried out in this paper and the conclusions obtained are as follows.(1)Shaking table test of shallow-buried,biased tunnel without damping layer was carried out.The acceleration and strain response laws of the measuring points of the lining under the action of Kobe wave and EI wave are obtained.When the input seismic wave is Kobe wave or EI wave,the type of seismic wave has little influence on the law of the horizontal acceleration amplification coefficient of the measuring point of the lining.When the input seismic wave is Kobe wave or EI wave,the type of seismic wave has a greater influence on the vertical acceleration magnification coefficient of the measuring point of the lining.The left shoulder of the tunnel lining has the strongest seismic response,which is an important consideration for seismic fortification.The strain of tunnel lining is easily affected by the intensity of excitation,the greater the intensity of excitation,the greater the strain.The peak tensile strain at the right shoulder of the lining is greater than the compressive strain.(2)The shaking table test of a shallow-buried,biased tunnel with damping layer was carried out.The acceleration and strain response laws of the measuring points of the lining under the action of Kobe wave and EI wave are obtained.When the input seismic wave is an EI wave,the horizontal acceleration amplification factor of the measuring point is less affected by the excitation intensity,and the vertical acceleration amplification factor is greatly affected by the excitation intensity.When the input seismic wave is Kobe wave,the horizontal and vertical acceleration magnification coefficients of the measuring point of the lining are greatly affected by the intensity of the excitation.At the left shoulder of the tunnel lining,the seismic response is still relatively strong.By analyzing the dynamic response law of shallow-buried,biased tunnels with or without damping layer,the damping effect of the damping layer is obtained.The setting of the rubber damping layer can reduce the peak horizontal acceleration of the lining measuring point by more than 24%,the peak vertical acceleration by more than 20%,and the peak strain by about 20%.(3)A numerical model of shallow-buried and biased tunnels with different thicknesses of rubber damping layers has been established.The damping effect of the rubber damping layer placed at the position where the dynamic response of the tunnel lining is larger is studied.When the thickness of the damping layer is 10cm,the axial force,bending moment and shear force at each measuring point on the lining will be reduced by about 15%,and the peak value of the principal stress will also be greatly reduced.The damping effect of this thickness damping layer is better.(4)A numerical model of shallow-buried and biased tunnels with annular steel plates at different intervals is established.The shock absorption effect of the ring steel plate installed in the tunnel boundary is studied.The setting of the annular steel plate will make the internal force distribution on both sides of the tunnel more uniform,which is manifested by the decrease of the internal force on the left side of the tunnel and the increase of the internal force on the right side of the tunnel.The setting of the annular steel plate will also make the stress distribution of the measuring points on both sides of the tunnel more uniform,but the stress at the local position will increase.The setting of the steel plate will reduce the peak axial force at the right shoulder of the lining by about 7%.When the ring steel plate spacing is set to 3m,it can have a better shock absorption effect than that of 4m.When the ring steel plate spacing is set to 3m,compared with the spacing of 2m,the damping effect is equivalent but it can save materials.It is more appropriate to choose ring steel plates with a spacing of 3m.The research on the damping effect of ring steel plates with different spacing is of great significance to improve the safety of the tunnel.