The Seismic Response And Seismic Property Of Large Section Tunnel With Unsymmetrical Loading Based On Shaking Table Test

With the rapid development of the national economy,in order to meet the increasing demand for traffic,the engineering examples of large section tunnel represented by four lane highway tunnel have been common.The large section tunnel is located in shallow buried bias section,the thickness of covering soil is thinner,the stress of lining structure is not uniform,it is easy to be destroyed in the high intensity earthquake area,but the seismic research of the large section shall.ow bias tunnel is still very scarce at present.Therefore,the study on the seismic response and dynamic characteristic of large section shallow bias tunnel is of great importance with respect to the scientific research and the engineering practice.Based on the expansion project of Jinjishan Tunnel in Fuzhou 2nd ring road,using the method of shaking table model test,the seismic response and dynamic characteristic of large section shallow bias tunnel are studied.The main conclusions are as follows:1)Under the excitation of various horizontal seismic waves,the PHA amplification coefficient upon slope increase nonlinearly with ground elevation,the PHA amplification coefficient in slope(including tunnel)increase logarithmically with ground elevation,it indicates that the large section tunnel has obviously changed the ground elevation effect.Because of the resonance effect,the elevation effect caused by EL wave excitation is obviously larger than the other 3 waves;2)Based on the Fourier analysis,it is considered that the existence of large section unsymmetrial loading tunnel changes the seismic property of original ground significantly when the site is soft and the buried depth is shallow.It is generally considered that the first predominant frequency(7.7Hz)mainly reflects the dynamic characteristic of the original site,while the second predominant frequency(24.0Hz)mainly reflects the dynamic characteristic of the tunnel lining structure.Based on the analysis of the frequency response function,it is considered that the frequency components near the second predominant frequency augment significantly when seismic wave propagates through the tunnel lining structure,and the maximum gain frequency is close to the second predominant frequency;3)Under the excitation of horizontal seismic waves with different amplitudes,the sensitivity of the seismic response of tunnel lining structure on backer side is much greater than that on the free surface side;in the small amplitude,the left arch foot is the most unfavorable position of lining structure,but in the large amplitude,the most unfavorable position shifted to the left arch waist;4)Under the excitation of horizontal seismic waves,the tunnel lining structure subjected to the circulation function of positive and negative bending moment;the flat rate of tunnel has a significant influence on the stress distribution of lining under earthquake.For large section tunnel,the stress of left arch foot and the left arch waist is maximum,the number of cracks,the transfixion degree of cracks and the width of cracks on backer side are obviously serious than those on free surface side,these sections are the key parts of earthquake fortification for large section shallow bias tunnel tunnel.