Seismic Response And Property Of Tunnel With Large Section

Mountain tunnel has long been considered to have good seismic performance,several large earthquakes occurred in recent years,however,there are a considerable number of mountain tunnel suffered varying degrees of damage.And the tunnel as a mountain area highway and railway control engineering,once the earthquake damage is often difficult to repair.Therefore,the seismic response and seismic property of the mountain tunnels under earthquake,is gradually becoming a research hotspot and difficult problem in academic and engineering fields.At the same time,with the rapid development of transportation infrastructure,large cross-section tunnel examples(Such as a 4-lane highway tunnel)have been common,but the related research of such large section tunnel seismic performance is relatively rare.Based on the expansion project of Jinjishan Tunnel in Fuzhou 2nd ring road,and shaking table model test of mountain tunnel with large section has completed,then a series of numerical simulation research have beam launched on FLAC3D5 0 numerical platform,and the seismic response and seismic property for the large section mountain tunnel are focused.(1)The results of numerical simulation and model test are compared and analyzed,and the peak seismic acceleration(PGA)amplification coefficient of tunnel model show the same regularity.The PGA amplification coefficients of tunnel model increase with ground elevation increasing,and decrease gradually with the augment of ground motion amplitude,then finally tends to be stable.As for the different frequency spectra of seismic wave excitation,the elevation effect caused by the abundant seismic wave excitation is more obvious when the amplitude is small,but the effect of the seismic wave frequency characteristics on the acceleration response also vanishes gradually.(2)Under the excitation of earthquake,peak seismic normal pressure of crown and arch bottom is not obvious,and the change of peak seismic normal pressure of arch foot and arch waist is very significant.With the augment of ground motion amplitude,the peak seismic normal pressure(PEP)oscillation coefficients upon sidewall and arch increase linearly in general.X-direction peak seismic lining moment gradually increases from crown to arch bottom,and with the augment of ground motion amplitude,the difference value of maximum peak moment and minimum peak moment(△Mx)at arch foot increases gradually.The characteristic of lining cracking after shaking table tests is also carefully inspected.The lining cracks develop parallelly with the tunnel alignment and concentrate on the sidewall,the arch and the invert respectively,which accords with the analysis of normal pressure responses.(3)The frequency-response analysis on the test results and numerical simulation results shows that the components around the 2nd predominant frequency(the properties of lining structure)augment significantly when the seismic wave passes through the lining structure,while the lnd predominant frequency(the properties of original ground)decrease gradually.The most-augmented frequency equals to the 2nd predominant frequency roughly.The most-augmented frequency of frequency response analysis on numerical simulation results is 4.7Hz,while the test results is 25.1Hz.The similarity of time/frequency is approximately satisfied,and verified the 2nd main frequency is the main frequency of lining structure.