Simulation Study on the Influence of the Distance between Two Boreholes on Seismic CT in Karst Detection
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摘要:
随着对地下空间开发的日趋增加，地下空间的施工与利用安全问题越来越受到广泛关注，地下发育的岩溶对于地下空间的开发会造成诸多安全隐患，对人民的生产生活也会造成很多影响。跨孔地震CT技术已经广泛应用于岩石破碎带、溶洞等探测，为地下空间的开发利用及施工安全提供了重要的技术支撑。为了进一步研究该技术的成像精度，本文对影响跨孔地震波初至CT成像精度的3个因素（孔间距、岩溶尺寸及水平间距）开展了正反演研究。研究结果表明：当孔深为20 m、孔间距为20 m时，该技术对直径为2.5 m单个岩溶的成像效果与其水平位置有关，而当孔间距缩小到15 m、10 m时，该技术对尺寸大些、岩溶水平间距大些的岩溶能很好地反演成像；对于多个岩溶水平或垂直排列时，当孔间距为10 m时，该技术能准确探明直径为1.5 m的岩溶。因此，在实际工作中，为了能准确探测到直径为1.5～2.5 m的岩溶，建议钻孔间距小于15 m。
Abstract: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.
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Keywords:
- seismic wave fist arrival /
- CT /
- Karst /
- distance between two boreholes
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图 1 跨孔地震CT观测系统示意图
Figure 1. Schematic diagram of the source receiver geometry for a cross-hole seismic CT
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图 2 模型1正反演结果（L=10 m, D=2.5 m）
Figure 2. The forward and inversion results of the first model
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图 7 模型6正反演结果（L=5 m, D=2.5 m）
Figure 7. The forward and inversion results of the sixth model
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图 3 模型2正反演结果（L=14 m, D=2.5 m）
Figure 3. The forward and inversion results of the second model
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图 4 模型3正反演结果（L=11 m, D=2.5 m）
Figure 4. The forward and inversion results of the third model
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图 5 模型4正反演结果（L=10 m, D=2.5 m）
Figure 5. The forward and inversion results of the fourth model
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图 6 模型5正反演结果（L=8 m, D=2.5 m）
Figure 6. The forward and inversion results of the fifth model
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图 8 模型7正反演结果（L=5 m, D=2.5 m）
Figure 8. The forward and inversion results of the seventh model
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图 9 模型8正反演结果（L=12 m, D=2 m）
Figure 9. The forward and inversion results of the eighth model
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图 10 模型9正反演结果（L=10 m, D=2 m）
Figure 10. The forward and inversion results of the nineth model
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图 11 模型10正反演结果（L=12 m, D=2 m）
Figure 11. The forward and inversion results of the tenth model
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图 12 模型11正反演结果（L=10 m, D=2 m）
Figure 12. The forward and inversion results of the eleventh model
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图 13 模型12正反演结果（L=5 m, D=2 m）
Figure 13. The forward and inversion results of the twelfth model
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图 14 模型13正反演结果（L=6 m, D=2 m）
Figure 14. The forward and inversion results of the thirteenth model
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图 15 模型14正反演结果（L=3.5 m, D=2.5 m）
Figure 15. The forward and inversion results of the fourteenth model
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图 16 模型15正反演结果（L=3.5 m, D=2.5 m）
Figure 16. The forward and inversion results of the fifteenth model
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图 17 模型16正反演结果（L=3 m, D=2.5 m）
Figure 17. The forward and inversion results of the sixteenth model
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图 18 模型17正反演结果（L=3 m, D=2 m）
Figure 18. The forward and inversion results of the seventeenth model
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图 19 模型18正反演结果（L=3 m, D=2 m）
Figure 19. The forward and inversion results of the eighteenth model
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图 20 模型19正反演结果（L=3 m, D=2 m）
Figure 20. The forward and inversion results of the nineteenth model
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图 21 模型20正反演结果（L=3 m, D=1.5 m）
Figure 21. The forward and inversion results of the twentieth model
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图 22 模型21正反演结果（H=3 m，D=2.5 m）
Figure 22. The forward and inversion results of the twenty-first model
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图 23 模型22正反演结果（H=3 m，D=2.5 m）
Figure 23. The forward and inversion results of the twenty-second model
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图 24 模型23正反演结果（H=5 m，D=2.5 m）
Figure 24. The forward and inversion results of the twenty-third model
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图 25 模型24正反演结果（H=3 m，D=2.5 m）
Figure 25. The forward and inversion results of the twenty-fourth model
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图 26 模型25正反演结果（H=5 m，D=2.5 m）
Figure 26. The forward and inversion results of the twenty-fifth model
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