Application Of Cross-hole Seismic Tomography In Karst Exploration

With the rapid development of the country and urban construction immediately behind,the demand for transparency in underground space has also increased accordingly.In the process of urban underground space engineering construction,the existence of bad geology seriously affects the quality and safety of engineering construction,while karst is The most common kind of engineering geological problem.The formation and development of karst is a complex geological phenomenon.Therefore,the forms of karst existing underground are also different.This undoubtedly brings huge complexity to the exploration project of geological bodies.However,when underground engineering construction is carried out in karst areas,it is not the same.Proved karst distribution will easily cause large-scale safety accidents such as water inrush and surface collapse,and the use of underground space for urban construction is extremely risky.Therefore,the fine detection of karst areas is carried out to divide the scope and distribution of karsts,so that the underground geological distribution can be visualized to a certain extent,which is of great significance for the development of urban underground space and the construction of engineering projects.In response to the requirements of refined detection of underground space engineering,the use of cross-hole seismic wave tomography methods to detect urban karst areas and summarize its imaging characteristics can better guide projectconstruction.The main research contents of this paper are as follows:(1)Establish generalized geophysical models of different karst types.There are caves and fracture zones of different shapes,directions,and sizes in the rock formations.A series of generalized geophysical models are established based on the physical characteristics of rocks,including the wave velocity and fault distribution of common rocks,and the types of karsts.(2)In order to better study the detection laws of cross-hole seismic wave tomography in urban karst areas,and guide actual engineering construction.In this paper,a series of generalized geophysical model numerical experiments are carried out based on the REFLEXW forward and inversion program,and the geophones and source offsets under a single anomaly body,the ratio of different hole spacing to borehole depth,and different anomaly body sizes and boreholes are carried out.Numerical simulation is carried out on the ratio of spacing,the ratio of height to width of different anomalous bodies,multiple anomalous bodies,and faults with different thicknesses and dips.The analysis and interpretation are carried out based on the numerical simulation results,and the response law of the cross-hole seismic wave tomography method to the karst area issummarized and verified.The feasibility of the method.(3)Relying on the Mufu Mountain karst exploration project of Nanjing Heyan Road Crossing Channel Project,the cross-hole seismic wave tomography method was adopted at the project site,the data was collected by seismograph,the REFLEXW program was used to invert the imaging,and the cross-hole was verified by the inversion imaging results.The feasibility of seismic wave tomography method in practical engineering application.The inversion results are subjected to 3D data extraction and imaging processing to obtain horizontal slices and vertical slices,and finally the three-dimensional distribution of geological bodies in the detection area is obtained through the threshold technology.