Study On The Application Effect Of Seismic Imaging Method In The Karst Exploration Of Tunnnel In Guizhou Section From Shanghai To Kunming High-speed Railway

The hazards of tectonic karsts are not only reflected in the construction,such as the lack of timely treatment or remediation treatment is not complete,in the latter part of the operation of the project constitutes a threat to the safety of the tunnel,endanger traffic safety,so how to accurately and effectively detect the karst development area is particularly important.Seismic imaging method is a fast and non-destructive testing method,and can be combined with seismic reflection wave,refracted wave,diffraction wave and other multi-wave information,the measured data analysis and interpretation is relatively simple.Although the method is less applied in the tunnel karst detection,combined with the actual exploration of this project,it is proved that the method has good effect and can effectively identify the distribution of the karst under the tunnel.Firstly,the theoretical basis of seismic image detection is introduced.Seismic wave in stratified media,propagation mechanism,time-distance curve equation,elastic wave dynamics foundation,elastic wave wave equation,the basic principles of seismic imaging method.Furthermore,the basic principles and general process of finite difference method are introduced.The Tesseral software is an commercial software which built on the basis of Finite-difference calculation.The Tesseral seismic wave simulation software was used to generate the seismic waves,and the seismic waveforms of the same offset were superimposed by the seismic processing software Vista.The wave field response characteristics of the single layer medium model,the void model,the low velocity body model and the hollow water filling model are obtained.Finally,the measurement technology and influencing factors of seismic imaging method are studied.The influencing factors mainly include excitation condition,receiving condition,coupling condition,offset factor,noise factor and so on.In this paper,based on the actual engineering survey,the wave field response characteristics of the geological bodies such as normal medium,dissolution zone and void media are obtained.The results show that the method has good effect on the detection of karst under the tunnel,and the detection speed is faster and the penetration distance is larger.Although there is some shortcomings in accuracy,it is a fast nondestructive detection method,can basically meet the engineering requirements.As a result of a single geophysical means to detect the karst under the tunnel,there may be a misjudgment to the actual interpretation result,we need to enhance the combination with the actual engineering.