Numerical Analysis Of The Seismic Response Of Circular Tunnels In Soil

Tunnels are popularly utilized around the world and play an important role in civil infrastructures,and the tunnel construction has been expanded year by year in China.Nevertheless,in seismically active areas,a large number of severe damage to tunnel structures were reported in recent earthquakes Therefore,as an important part of lifeline engineering,the seismic design of the tunnel must be highly valued.Many researchers have carried out extensive study on the seismic damage mechanism and seismic design method of the tunnels,etc,and obtained meaningful results.In this paper,the author study the response of tunnels using the finite difference method.The main work and achievements are as follows:1.The review of the seismic response of tunnelsOn the basis of summarizing the existing earthquake disasters of tunnels,recent progress in some critical issues of tunnel structures are summarized,including four aspects:earthquake damage mechanism,seismic response influence factors,application of response displacement method for seismic design of tunnel structures,as well as model tests of tunnels.2.The effect of Rayleigh damping on the site seismic responseNumerical models are developed to simulate the wave propagation through an elastic medium after considering soil thickness H,shear velocity V_S and spectral characteristics of input motions.A full Rayleigh damping matrix is adopted and the low frequency is selected as the fundamental site frequency,the high frequency is determined by five methods.In order to compare the results of different methods with actual records,the equivalent linearization method and time-domain with five damping formulations on the seismic response of soil layers in Xiang-tang Array are also presented.Furthermore,we discusses the reasons that cause the difference,and recommend the Rayleigh damping matrix.3.The basic feature of the seismic response of circular tunnelsThis part investigates the soil plasticity on the seismic response of circular tunnels constructed in soft soil.Visco-elastic and elastoplastic constitutive models are adopted to describe the soil dynamic behavior under earthquake loading respectively,to explores the divergence that with and without considering the soil plasticity in order to assess its importance on the seismic response of circular tunnels.Then,the effects of Rayleigh damping matrix on the seismic response of tunnels are also discussed.Finally,numerical models are developed to simulate the seismic response after considering various buried depths,diameters,thicknesses and diameter-to-thickness ratios.4.The influence of the tunnel on the surface horizontal accelerationsThe effect of the circular tunnel on the ground surface horizontal acceleration is analyzed by using the numerical method herein.The Ricker wavelet with wide range of frequency is selected as the input dynamic motions,considering different tunnel depths,lining thickness,shear wave velocity of soil,shear wave velocity ratio of lining and soil and frequency of input motions.Moreover,three actual ground motions are also used to verified the conclusions obtained.