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超前地质预报是隧道施工中必不可少的环节,将地面三维电阻率E-SCAN观测模式引入到隧道超前预报中,其中供电与采集电极都布置在隧道掌子面,可有效降低旁侧干扰因素的影响,提出了基于三维电阻率E-SCAN的隧道超前探测新型观测模式。建立了隧道三维电阻率E-SCAN超前探测地电模型,获得了敏感度矩阵分布特征:矩阵元素数值较小且相差悬殊;元素绝对值随深度衰减迅速;靠近供电与采集电极位置元素绝对值较高。为改善反演的深度定位问题,对敏感度矩阵中元素施加不同大小的增益因子,对原有敏感度矩阵中高值元素进行抑制,对低值元素进行增益,形成了基于敏感度增益因子的隧道三维电阻率E-SCAN超前探测反演优化方法,在理论上可以提高异常体的深度定位精度。开展数值算例与物理模型试验研究,结果表明在隧道三维电阻率E-SCAN超前探测中,相较于常规光滑约束反演,反演优化方法在异常体的深度定位精度方面具有明显优势。
The advanced geological prediction is an indispensable link in the tunnel construction. The three-dimensional surface resistivity E-SCAN observation mode is introduced into the advanced prediction of the tunnel. The power supply and collection electrodes are arranged on the tunnel face, which can effectively reduce the lateral interference factors , A new observation mode based on three-dimensional resistivity E-SCAN is proposed. The three-dimensional resistivity E-SCAN tunneling probing geoelectric model was established and the sensitivity matrix distribution was obtained. The matrix elements have small values and great disparities. The element absolute value decayed rapidly with the depth. The absolute value of the elements near the power supply and collection electrodes high. In order to improve the depth localization of the inversion, different sensitivity factors are applied to different elements of the sensitivity matrix to suppress the high-value elements in the original sensitivity matrix and gain the low-value elements to form a tunnel based on the sensitivity gain factor Three-dimensional resistivity E-SCAN advanced detection inversion optimization method, in theory, can improve the depth of abnormal body positioning accuracy. Numerical examples and physical model tests are carried out. The results show that in the E-SCAN advanced detection of tunnel three-dimensional resistivity, the inversion optimization method has obvious advantages in the depth positioning accuracy of the anomaly compared with the conventional smooth constraint inversion.