| Since the development of the CHR series of EMU in 2006,rapid development of high-speed railways in China has inevitably encountered a series of projects such as bridges and tunnels,especially in hills and mountainous regions in Southwest of China.The tunnel construction is often affected by a variety of geological problems,encountering the prediction of bad geological bodies before the tunnel construction is related to the progress of entire project and the safety of construction personnel.So tunnel geological advanced forecasting is necessary.In this paper,Multi-seismic reflected wave method is used to study tunnel models of different karst caves’ two-dimensional wave field snapshots、seismic trace records and wave field separation characteristics.The main research contents are as follows:(1)Study the effect of simulated source force on the vertical direction.(2)Numerical models of cave with different diameter and filling material and different distance from the bottom of tunnel face which are in front of tunnel face and directly in front of the bottom of tunnel face are established.Studying and analyzing seismic trace records of horizontal and vertical components、snapshot characteristics of wave fields at different times and using τ-ρ filtering separates wave field.(3)The travel time of reflected longitudinal wave to the first geophone and the last geophone is read through seismic trace record,then writing program to calculate the location of cave.The following conclusions are obtained in the above research content:(1)There are good trace records obtained by loading the simulated source in vertically upwards or downwards,these seismic waves have a high degree of recognition.However,it was found there are some high-frequency noises after superimposing the horizontal or vertical component seismic trace records in the above two directions to synthesize new horizontal and vertical component seismic trace records,which means the characteristics of seismic sources such as explosions in the vertical and other opposite directions within the scope of our study can almost cancel each other out.Therefore,the simulated source loading direction is horizontal to the direction of the excavation of the palm face in subsequent numerical simulation calculation.(2)In snapshots of model wave field,body waves propagate in the form of spherical waves,their energy continue to decay as distance increases;with strong energy and slow propagation velocity are shear waves,and with weak energy and fast propagation velocity are longitudinal waves;under the same component,the energy reflected by a large-diameter cave is strong,the energy reflected by a small-diameter cave is smaller with the same tunnel medium and the same cave filling material;the energy of direct longitudinal waves and longitudinal wave reflected waves in horizontal component is stronger than the vertical component.(3)In seismic trace records,the energy of each reflected waves of cave with a smaller diameter is weaker,whereas the energy of each reflected waves of cave with a larger diameter is stronger when other parameters of the model are same;the time of each reflected waves is shorter in seismic records where are cave models with small distance from bottom to tunnel face when other parameters of the model are same;the energy of reflected waves of the water-filled cave model is stronger than the energy of reflected waves of the cavity model when other parameters of the model are same.(4)TLongitudinal and shear waves are in good agreement and have a high degree of recognition after wave field separation;the vertical component has a more sensitive response to shear waves,so vertical component wave field separation results of each model are better than horizontal component.(5)According to travel time of the reflected longitudinal wave that arrives faster and has a higher degree of recognition to the first geophone and the last geophone,the results of calculated cave position are highly reliable. |
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