| In recent years,with the promotion of the western development and "One Belt One Road" initiative,the road construction in the loess area of China has developed rapidly.Due to topographic constraints,engineering costs and other factors,double-arch tunnel form is gradually adopted when crossing the gully-ridden loess area.Loess has dynamic vulnerability characteristics,and the northwest loess belongs to the strong earthquake prone area,earthquakes may easily cause slope collapse,lining structure damage and other earthquake damage.At the same time,the overlying soil of double-arch tunnel has some problems,such as bias pressure and deformation coordination between double-arch tunnels,so that the dynamic response is more complicated than that of single tunnel.Therefore,it is of practical significance to study the seismic dynamic characteristics of shallow buried biased double arch loess tunnel and slope in loess region.This paper summarizes the current situation of the research on the dynamic response of the slope tunnel system and the slope body of the tunnel containing double-linked arches in loess areas,and analyzes the displacement,acceleration and stress-strain response of the slope tunnel system through numerical simulations and model tests;On the basis of this,the wavelet packet transform(WPT)and Hilbert yellow transform(HHT)are used to investigate the fluctuation characteristics of the slope surface and lining structure,the main contents and results are as follows(1)Numerical simulation of shallow buried biased double arch tunnel.The presence of the tunnel will have an inhibitory effect on the displacement response within the slope.When different types of seismic waves are loaded,the displacement,acceleration and stress-strain caused by EL waves are the largest,and the damage to the slope and lining is the strongest,followed by Minxian waves and the smallest by Lanzhou artificial waves.(a)The excitation direction perpendicular to the tunnel axis in the vertical plane(Z)and the excitation direction perpendicular to the tunnel axis in the horizontal plane(X)cause a larger response of the slope and tunnel structure,while the loading direction parallel to the tunnel axis in the horizontal plane(Y)produces a smaller response;The amplification factor of slope acceleration caused by seismic waves in different directions peaks at different locations on the slope: in the X direction at the top of the slope,in the Y direction at the waist of the slope,and in the Z direction near the waist of the slope;Coupled loading results in stronger response in each direction.(2)Dynamic characteristics of shaking table in shallow buried biased double arch tunnel.According to the earthquake damage phenomenon and displacement response law,the slope damage to damage process is divided into elastic-plastic deformation accumulation stage,critical damage stage and overall damage stage.The slope acceleration response pattern shows that the elevation amplification effect is obvious,producing peak displacement and PGA amplification coefficients at the top of the slope.When the seismic intensity is small,the strain difference of each measurement point is smaller;when the input seismic wave peak is larger,the local damage effect is more significant.Because of the shallow burial depth,the strain of the tunnel shallow buried side should be changed,and its force is more unfavorable.The accuracy and reasonableness of the two research methods and the research results were verified by comparing the shaker test with the numerical simulation results.(3)Study on the wave characteristics of slope tunnel system caused by earthquake.The low frequency wave(≤20Hz)is the main cause of slope damage,and the low frequency wave energy increases significantly as the intensity of ground shaking increases.The Hilbert spectrum of the slope surface is characterized by "small and concentrated peaks at the foot of the slope and large and discrete peaks at the top".High-frequency waves cause integral vibration of the tunnel structure,while low-frequency waves cause local damage to the weak parts of the lining structure;the energy distribution increases with the seismic intensity in the low-frequency domain,and the opposite in the high-frequency;the peak energy response changes with the burial depth and whether the slope is reinforced or not.The Hilbert spectrum distribution pattern around the tunnel inside the slope shows the characteristics of "low intensity waves(0.1,0.2g)are more abundant in the high frequency band and have a longer duration of action,while high intensity waves(0.8,1.0g)are dominated by low frequency and have a short duration of action".(4)The effect of frame lattice beam reinforcement on the reduction of slope and tunnel dynamic response is obvious.Comparing the peak displacement,peak acceleration amplification coefficient,peak tunnel strain and peak Hilbert spectrum distribution of the unreinforced and reinforced sides of the slope,it can be seen that the reinforcement measures can effectively reduce the peak dynamic response. |
