基于井间电磁波CT在浅地层溶洞探测中的正反演

Forward and Inversion Modelling of Cross-Hole Electromagnetic Wave Computerized Tomography in the Shallow Cave Detection

浅层溶洞探测是岩溶地区地铁工程建设中面临的主要地质难题。传统钻探手段不能完全解决特殊性溶洞的问题,运用井间电磁波CT成像新地球物理技术,在其基本原理的基础上,通过建立地质体理论模型,对3种反演算法成像图进行对比,得出联合迭代重建算法(SIRT)反演效果最好;利用SIRT研究双溶洞中心点之间不同距离对溶洞勘查的影响,得出当溶洞中心点之间的距离为8m及3m时,都能有效识别出2个溶洞的形状;当中心点距离为1m时,双溶洞在反演等值线图中呈现为1个溶洞异常。选用联合迭代重建算法(SIRT)并应用于某地铁线溶洞勘查项目中,取得了较好的应用效果。

The shallow cave detection is one of the main geological problems of the subway engineering construction project in the karst region.The traditional drilling method cannot completely solve the problem of the particular karst cave.The cross-hole electromagnetic CT imaging technique is a new geophysical technique developed in engineering geophysical field in recent years.Based on the fundamental principles of cross-hole electromagnetic wave CT imaging technique,this study established theoretical models of geological bodies to compare images of 3 inversion algorithms.The result shows that the effect of simultaneous iterative reconstruction technique（SIRT）inversion is the best.Meanwhile,the SIRT is used to evaluate the influence of different center distance of two caves in the exploration.It is concluded that the shape of the double caves can be effectively identified when the center distance is 8 meters and 3 meters.However,the double caves appear as one anomaly in the inversion contour map when the center distance is 1 meter.The simultaneous iterative reconstruction technique（SIRT）is applied to the cave exploration of a subway project,which has achieved good application results.