Experimental Study On Shock Absorption Of Closed Hole Foam Aluminum Lining In High Speed Rail Tunnel

"Belt and Road Initiative" is China geo economic,geopolitical and geo century strategic security.Four of the high-speed rail lines are planned:Eurasian high-speed rail,Central Asia high-speed rail,Transasia high-speed rail,high-speed rail connecting China,Russia,Canada and the United states,the initial estimated total mileage of more than 40 thousand km.First,a large number of tunnel projects are inevitable due to the high requirements of the ride comfort of the high-speed rail.Second,the span of the line causes it to be unable to avoid passing through the seismic fault zone.The Eurasian high-speed rail and Central Asia high-speed rail cross the Eurasian Earthquake Fracture zone,Transasia high-speed rail and high-speed rail connecting China,Russia,Canada and the United states through the Pacific seismic belt piercing.Therefore,it is of great significance to solve the problem of shock absorption of high-speed railway tunnel.This paper uses a new type of damping materials closed-cell aluminum foam as the damping layer,which instead of the traditional damping materials,carried out a large earthquake simulated shaking table test in order to verify the actual damping effect,the main research results are as follows:(1)Study on the basic mechanical properties of closed cell aluminum foam material through static and dynamic compression test,static to different density of aluminum foam compression test results show that with the increase of density,compression platform material stress ?pl increases,densification strain?D decreased gradually.The dynamic compression test stress-strain curves of severe shocks,no obvious regional platform;with the increase of the strain,the stress increases after the first emergency relief,but has been increased,and appeared in the shock region repeated stress fluctuation.The peak value of dynamic compression is higher than that of static compression,and the peak value of stress increases gradually with the increase of density.The compaction strain of foamed aluminum material of different density is different greatly.(2)The energy absorption efficiency,E and ideal energy absorption efficiency of closed cell aluminum foams,I were quantitatively analyzed,the maximum stress corresponding to the maximum energy absorption efficiency of closed cell aluminum foams with different densities is different,the smaller the material density is,the lower the stress level of the ideal energy absorption efficiency is,in other words,under low stress level,the greater energy absorption efficiency can be achieved.According to the constraint condition of foam aluminum damping layer in shaking table test in this paper,material selection and design of shock absorption layer.Finally,the closed cell aluminum foam with density of 0.13g/cm3 and the thickness of 20mm are adopted as the shock absorption layer of the tunnel lining structure.(3)The surrounding rock model materials are developed.According to the requirements of the similarity scale,the river sand,engine oil and fly ash are used as raw materials.Through orthogonal experimental design,the primary election of the mix proportion materials was carried out,then,based on the Mohr-Kulun shear strength theory,two screening methods are carried out.Finally,the optimum ratio(mass ratio)of the surrounding rock model materials is as follows:river sand(23%),oil(12%)and fly ash(65%).Gypsum is chosen as the model material of the two lining structure of tunnel,six groups of paste ratio specimens were designed by experiments.The required modulus of elasticity of the model material was used as the mechanical index to calculate the water ratio of the tunnel model.The ratio of paste to water was 1.41:1.0.(4)The dynamic response of interval tunnel model with or without damping layer is analyzed.The results show that the maximum acceleration attenuation coefficient Ka of most loading cases is less than 1,the shock absorption effect of the foam aluminum damping layer is confirmed.But for different seismic waves,the amplitude of shock absorption is different,in Kobe seismic wave loading,the acceleration extreme value attenuation coefficient is between 0.67-0.94,the Northridge seismic wave acceleration extreme value attenuation coefficient is between 0.75?0.95,and the artificial wave acceleration extreme value attenuation coefficient is between 0.79?0.97.(5)The dynamic response of the portal section model with damping layer is analyzed.Three monitoring sections of shallow buried section,variable slope point and deep buried section are set up in the test.The acceleration response of the deep buried segment is smaller,which shows that the deep tunnel is beneficial to the seismic design.Because of the different buried depth of the surrounding rock on both sides of the tunnel,the lining structure is affected by unbalanced seismic force and the seismic response is larger.The shallow section and the variable slope point are the key fortification parts of the shock absorption design,in most cases,the variable slope is the most unfavorable,the shallow buried section is second,and the deep buried section has the least dynamic response.(6)Based on the theory of seismic wave reflection and attenuation of refraction energy,introduced the energy dissipation ratio W as the measure of dissipative energy in the shock absorbing layer.The change law of the energy dissipation ratio with the incidence angle is analyzed,and the shock absorption mechanism of the damping layer based on reflection and refraction theory is revealed,according to the angle of incidence of different monitoring points in this experiment,the mechanism is one of the important reasons for the different damping effects of different monitoring points.(7)A three-dimensional numerical model is established by using the finite difference software FLAC3D,the displacement field and stress field distribution of surrounding rock under different loading conditions are studied,which provides a scientific theoretical support for the dynamic response analysis of tunnel structures.The numerical analysis method is used to calculate the loading conditions,and the calculated values are compared with the experimental ones,The analysis results indicate that the calculated values are close to the test value,indicating that the model test can simulate the response of tunnel and surrounding rock system under earthquake.It is a new attempt that the closed cell aluminum foam is used as the lining layer of the tunnel lining,on the whole,good damping effect has been achieved.It provides effective experimental support for the study of seismic resistance of tunnel structures.