Simulation Study on the Influence of the Distance between Two Boreholes on Seismic CT in Karst Detection

With the increasing development of underground space, the safety of underground space construction and utilization has drawn widespread attention. The development of underground karst will not only cause many hidden safety hazards to the utilization of underground space, but also affect people's normal life. Cross-hole seismic CT technology has been widely used in the detection of rock fracture zones, karst caves, etc., which has provided important technical support for the development and utilization of underground space and construction safety. In order to further study the imaging accuracy of this technology, this paper has carried out forward and inversion research on the three factors (the distance between two boreholes, karst size and horizontal spacing) that affect the accuracy of cross-hole seismic wave first arrival CT imaging. The results of the study show that: when the hole depth is 20 m and the distance between two boreholes is 20 m, the imaging result of this technique on a single karst with a diameter of 2.5 m is related to its horizontal position, and when the distance between two boreholes is reduced to 15 m and 10 m, the technique can successfully construct the karsts with large sizes and large horizontal spacing; when multiple karsts are set horizontally or vertically, this technology can accurately detect karsts with a diameter of 1.5 m when the distance between two boreholes is 10 m. Therefore, in practical applications, it is recommended that the borehole spacing should be less than 15 meters in order to accurately detect karsts with a diameter of 1.5~2.5 m.