基于跨孔电阻率CT的地铁盾构区间孤石探测方法及物理模型试验研究

Boulder detection method for metro shield zones based on cross-hole resistivity tomography and its physical model tests

跨孔电阻率CT方法在地铁盾构区间孤石探测方面具有一定优势,但仍然存在孤石定位精度低、小尺寸孤石难以识别等工程实际难题。首先,提出了电阻率CT不等式约束反演成像方法和偏导数矩阵的并行解析快速求解方法,从施加先验信息约束和提高反演精度两个方面共同改善了电阻率CT反演的多解性与成像效果。在此基础上,通过大量常规观测模式的成像效果对比试验,提出了一种组合式观测模式,可以综合多种常规观测模式的探测优势并增加采集的数据量,从而提高对异常体的识别能力。针对影响探测效果的两个因素——孔距和电极间距进行了数值模拟试验研究,获得了在组合式观测模式下的有效孔距范围和合理的电极间距参数,并进一步检验了对小粒径孤石的识别效果。在此基础上,提出了地面物探普查与电阻率CT详查相结合的孤石探测方案。最后,开展了物理模型试验研究进行验证,探测结果与实际情况比较一致,具有较好的应用前景。

The cross-hole resistivity tomography method has certain advantages in boulder detection in metro shield zones, but some practical engineering problems, such as low location accuracy and difficult identification of small-size boulders, still exist.First of all, the inequality constrained inversion imaging method and the parallel analytical fast solving method for partial derivative matrix are proposed for reducing the multiple solutions and improving the imaging results in cross-hole resistivity inversion. On this basis, a combined detection mode is raised from numerous results of inversion imaging comparison experiments by routine detection modes. The advantages of various routine detection modes and the collected data amount are integrated in this mode, which is good for improving the recognition ability of abnormal bodies. Then, numerical simulation tests for borehole distance and electrode spacing which affect the detection results are performed. Under the combined detection mode, the effective range of borehole distance and the reasonable electrode spacing parameters are obtained. Further tests on the identification effects of small-size boulders are carried out. On this basis, the boulder detection scheme, which combines the ground geophysical screening and cross-hole resistivity tomography detection, is put forward. Finally, physical model tests are carried out to verify this method. The detection results are almost the same with the actual situation, so the proposed method has good application prospects.