| Loess is widely distributed in China,and the loess plateau is a strong earthquake-prone zone.The study of the seismic dynamic response characteristics and deformation and failure mechanism of loess tunnel can provide effective suggestions for the seismic design of loess tunnel,which is of great significance to protect people’s life and property safety and travel safety and disaster prevention and mitigation.At present,the researches on seismic fortification of tunnels are mostly focused on rock tunnels,while the researches on loess tunnels are relatively few.Therefore,based on the actual project of a certain loess tunnel in a passenger dedicated liner,considering the slope height,slope Angle and the elevation of the tunnel,combined with the research content of this paper.Three groups were selected from several groups of large shaking table model tests completed by the research group,through comparative analysis of the results of the three groups of shaking table model tests.It emphasizes on analyzing and studying the seismic dynamic response characteristics and deformation and failure mechanism of loess tunnel from the angle of acceleration response.The main research contents and results are summarized as follows:(1)By observing and recording the loading process of three sets of shaking table model tests,the loading failure process of the model was divided into four stages: early loading,middle loading,late loading and complete failure.On basis of it,through the analysis of the seismic acceleration data collected by the experiment,the variation law of the peak acceleration of the measuring points on the slope,the invert and the crown in the elevation and the longitudinal direction of the tunnel is studied and analyzed,which verifies the rationality of the stage division.(2)The wavelet packet transform method is introduced into the processing mode of seismic acceleration signal,and the fine analysis of frequency spectrum information is realized by MATLAB programming.The three groups of model test acceleration signals are processed by wavelet packet and the energy proportions of each frequency band are extracted.By analyzing the energy proportions of each frequency band,it is found that low-frequency components(0.1～12.51Hz)dominate in the process of instability and damage of the tunnel,accounting for more than 90% of the entire loading failure process,and the low frequency components are mainly controlled by the wave in the first frequency band(0.1～6.25Hz).By analyzing the energy ratios of the first frequency band E1 and E2 in the second frequency band,it is found that E1 and E2 fluctuate one after another.The higher the earthquake intensity is,the greater the energy ratio of the low frequency components is,and the more serious the damage degree of the model is.It is shown that the damage of the model is mainly caused by the low frequency components.(3)By analyzing the variation law of the energy ratio of the first frequency band E1 of the acceleration signals of measuring points at different positions with the loading condition,it is found that E1 will increase suddenly after a period of decreasing trend,and then repeat this law.Through comparison and analysis,it is found that this change of E1 corresponds to the four failure stages mentioned above,and can be used as a sign for the model to enter the next stage,which again verifies the accuracy of the division of the loading failure stage.(4)The deformation and failure mechanism of the three groups of models was analyzed and summarized: the common part of the three groups of models that is most easily damaged is the tunnel entrance,and the soil of the crown is seriously damaged when entering tunnel at2/3H.Through comparison,it is concluded that the model 1 with the slope foot into the tunnel,the slope angle of 60°,and the slope height of 96 cm has the slowest cumulative deformation damage and can withstand the largest deformation and seismic performance is the best. |
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