Study On Numerical Simulation And Application Of 3D Seismic Tomography For Karst At The Bottom Of The Tunnel In Chenggui High-speed Railway

High-speed rail tunnels often cross very complicated karst areas,and geological structure,structural characteristics and disease development degree at the bottom of tunnels will directly affect the safety of driving.Therefore using advanced and accurate detection technology to identify the form,scope and depth of tunnel karst development is of great significance for maintaining smooth lines and ensuring normal operation of lines.In this paper,the three-dimensional seismic tomography is applied to the detection of the disease of the high iron tunnel for the first time.The three-dimensional velocity imaging of the tunnel structure can be realized,and the location,shape and scale of the karst development can be accurately judged.The detection accuracy is far higher than the conventional geophysical methods.Three dimensional seismic tomography is a method to invert the three-dimensional structure of the region by using a large number of seismic observation datas,and this method is applied to the detection of the high iron tunnel,the following researches are done in this paper:(1)In view of the complex structure at the bottom of high iron karst tunnel in mountain area,a set of forward and inversion theory is summed up for three-dimensional seismic tomography of tunnel bottom karst,and the forward and inversion method of three-dimensional seismic tomography for the tunnel bottom is studied.(2)Through the establishment of a large number of forward models,the propagation modes of reflected seismic primary waves in different stratum structures are simulated,and the numerical simulation results of various typical karst tunnels are obtained.On the basis of the forward modeling,the inversion study is carried out,and the real velocity model is carried out by using the datas of the travel time of the seismic waves on the basis of the initial model.(3)The three-dimensional seismic wave response of karst and its influence areas in the tunnel medium model is simulated,and the seismic wave's response characteristics of karst areas are analyzed.(4)A three dimensional observation system,a source excitation mode,a geophone coupling mode and a data processing flow suitable for tunnel bottom seismic detection are developed.(5)Based on the three dimensional seismic datas collected from chenggui high-speed railway tunnels,combined with geological datas,the three dimensional velocity structure of tunnel bottom is reconstructed according to the numerical simulation done before.And the structures and medium composition of the tunnel bottom are analyzed,and the imaging is done.Finally,the inversion results are compared with the actual geological datas,and the application effect of three dimensional seismic tomography is quite ideal.