## 1 Introduction  
With the extensive development of engineering, those in construction have realized the importance of karst more and more, and began to conduct comprehensive analysis and research. This includes comprehensive analysis and research on the formation environment, influencing factors, types, geological and geomorphological features of karst and have achieved good results which are widely used in engineering geology. Under the dissolution of surface water and groundwater, different types of karst landforms and forms appear in nature, which largely destroy the integrity of rocks, and also affect the stability of rocks. With the development of social economy, more engineering projects need to be established in karst areas, and geological exploration in karst areas is increasingly valued by construction units. In the actual exploration and detection process, different technical means should be adopted according to the actual situation to better serve the project construction. At the same time, the development degree of karst will affect the normal construction of water conservancy, railways, highways, bridges and other construction projects. As the scale of engineering buildings in karst areas continues to expand and the number continues to increase, how to improve the detection and exploration technology in karst areas is an important issue faced by exploration units [1; 2; 3; 4]. Therefore, in order to improve the quality and effect of exploration, the exploration personnel should adopt scientific and reasonable methods according to the characteristics and nature of karst. Inengineering construction, adverse geological bodies, such as karst caves, fracture zones and fault fracture zones, are often encountered. If the existence of adverse geological bodies and their water content cannot be detected in advance, serious potential safety hazards will be buried, which is very likely to cause casualties, construction delay and major economic losses. At present, for the process of detecting adverse geological bodies in karst development areas, the traditional borehole survey is mainly used. This not only requires a heavy workload, long process time and high cost, but it is also a limited and backward technology. For some areas with complex geological conditions, it is often easy to have faults, broken zone karst, underground rivers and other areas with unfavorable geological structures; since the survey results are not ideal, it is difficult to reflect the actual geological conditions. The GPR method is a fast, nondestructive and high-resolution detection method, which is very sensitive to water-bearing bodies and is very suitable for the detection of adverse geological bodies. However, due to the limitation of the detection depth, the general geological radar is not suitable for detecting the deep stratum structure. In order to obtain the structural information of deep strata directly, it is often necessary to drill holes, but because of the \"one-hole view\", it is very easy to miss the source of disasters. By placing the antenna into the existing borehole, the occurrence of adverse geological bodies within a certain range around the borehole can be obtained, which can effectively solve the problems of limited detection depth and one-hole view of ordinary GPR. However, the borehole radar technology is not directional, and it is difficult to survey the small-size adverse geological bodies around the borehole [5; 6; 7; 8; 9]. Therefore, how to use a small number of boreholes and new survey technologies to accurately describe the structural characteristics of these unfavorable geology, speed up the progress of engineering surveys, reduce the cost of engineering, reduce the harm of unfavorable geology on the project, and ensure the safety and stability of the foundation are the difficulties and hotspots of current engineering geological surveys. To sum up, these common problems are the lack of a fast, accurate and advanced comprehensive survey technology [10; 11; 12; 13; 14].