Application Research Of Integrated Geophysical Exploration Technology In Underground Karst Exploration

China is a country with topography,geological conditions and complexities,and karst geology has a wide distribution,Especially in the southwestern region,carbonate rocks are more widely distributed.The long-term erosion of groundwater on carbonate rocks has formed a variety of karst landforms.Due to the rapid development of human engineering construction,the frequency and intensity of karst collapse are increasing,and the damage is also increasing.Due to the uncertainty,randomness and concealment of karst development,the complex causes of karst cause difficulties in the detection of caves.The multi-solution of geophysical methods and the complexity of karst cause a single geophysical method to have many defects in solving practical problems.The application of integrated geophysical methods makes karst detection more comprehensive and accurate,and has achieved good detection results.In this Thesis,according to the actual geological conditions,physical characteristics and site conditions of the project,different geophysical methods are selected for different parts of the project.Through the analysis of the advantages and disadvantages of different geophysical methods combined with engineering practice,three methods of transient electromagnetic method,high-density electric method and borehole electromagnetic wave CT were selected for exploration.The article is based on the theoretical basis and working principle of the three methods,the physical parameter model is established in combination with the actual project,using Matlab to write a one-dimensional transient electromagnetic method forward program,and the forward modeling and inversion calculations are performed on the high-density electrical method and the borehole electromagnetic wave CT using software,it aims to understand the response characteristics of different geophysical methods and provide a basis for the processing and interpretation of engineering actual data.The theoretical research results are applied to engineering practice and have achieved good application results,indicating the correctness of the research results.Due to the limitation of actual terrain conditions,the high-density resistivity method cannot detect the depth of karst detection,and the detection depth is generally only 1/6 of the length of the section or even smaller.The use of equivalent anti-magnetic flux transient electromagnetic can't solve the problem of shallow blind zone fundamentally,but it can effectively reduce the shallow blind zone and detect deeper karst.On the basis of boreholes,some of them are selected for electromagnetic wave CT detection to explore the scale and extension of karst in detail.The combination of depth and shallowness of different geophysical methods and complementary advantages make the geophysical results more accurate.Finally,based on the geophysical data,combined with the geological data of the borehole and the field survey data,the scope and characteristics of the disease were determined,and the areas where the karst and dissolution fissures were concentrated were relatively reliably identified,and good engineering application results were obtained,and provide reference for karst exploration under similar geological conditions in southwest China.For the detection of karst development area,the geophysical prospecting method with high efficiency(e.g.high density resistivity method)should be used first to carry out the survey,use other geophysical methods for further detection of areas with anomalies,if necessary,use drilling methods to verify,select some boreholes for tomographic imaging between boreholes,it is used to accurately identify the extension of the location of the karst and avoid the occurrence of geological disasters.