多同性源阵列电阻率法隧道超前探测方法与物理模拟试验研究

直流电阻率法以其对含水构造响应敏感且适应性强的特点,是隧道施工期超前地质预报的常用方法.针对目前定点源三极观测方式易受到测线附近旁侧异常干扰与聚焦观测方式探测距离过短无法三维成像的问题,提出了一种基于多同性源阵列电阻率的隧道超前探测新方法,利用环形布置的多同性源供电压制隧道掌子面后方的异常体的干扰,同时增强掌子面前方远处异常体的敏感度,阵列电极测量可为含水构造的三维反演成像提供三维数据.首先,开展了含水构造超前探测的数值正演模拟,发现多同性源方法的视电阻率纵向微分曲线极小值以及与横轴的交点位置可对异常体位置进行定性判断,探讨了多同性源方法对后方及侧向异常干扰的响应特征及识别方法.其次,将电阻率光滑约束与轨迹光滑策略引入蚁群反演算法,提出了一种最小二乘方法与改进蚁群算法相结合的混合反演算法,反演数值算例表明混合反演算法能够实现含水构造的三维成像,较好地反演出不同距离的含水构造位置,并使其边界较为清晰.为了验证多同性源探测方法的探测效果开展了物理模型试验,多同性源阵列电阻率法能较好的反映含水构造的存在,与实际含水构造的位置较为相符.

Advanced detection and physical model test based on multi-electrode sources array resistivity method in tunnel

Direct current resistivity method with sensitive response to water-bearing structure and strong adaptability is widely used in tunnel advanced detection. Because the fixed-point source three-electrode observation mode is easily affected by abnormal interference close to the survey line and the short detection distance of focused electrical observation mode without 3D tomography capability, a new technique based on multi-electrode sources array resistivity method is proposed in tunnel advanced detection.In this method, several measuring electrodes are arranged on the tunnel face to form the measuring system (i.e. the electrode M) to acquire data for the water-bearing structure's 3D inversion tomography, while 4 current electrodes are annularly arranged around the tunnel face to form the current system (i.e. the electrode A) which is used to suppress the abnormal interference behind tunnel face and increase the sensitivity to the distant abnormal bodies ahead of tunnel face. Simultaneously, the resistivity smooth constraint and trajectory smooth strategy are introduced into the ant colony optimization inversion algorithm, and the mixed inversion method combining least squares algorithm with improved ant colony algorithm is proposed. It takes the advantages of both linear and nonlinear inversion to overcome the shortcomings of linear inversion which is easily trapped into local optimum and to improve the efficiency of nonlinear inversion.The forward numerical simulation for water-bearing structure's advanced detection is carried out to investigate the response characteristics of abnormal bodies with different thickness, different electrical parameters and different distances. It is discovered that the minimum value of apparent vertical differential conductance curve and its intersection of horizontal axis have significant positive correlation with the abnormal body's position. In the range of 0~10 m, the minimum value L₁ of apparent vertical differential conductance curve is about 0.3 to 0.45 times that of the abnormal body's position d. In the range of 14~30 m, the intersection L₂ between apparent vertical differential conductance curve and horizontal axis is about 0.85 to 0.95 times that of the abnormal body's position. It means that the minimum value of apparent vertical differential conductance curve and its intersection with horizontal axis can be used to roughly determine the abnormal body's position, which can serve as initial model to provide prior information for inversion position. Then the proposed mixed inversion method is applied in numerical simulation and model experiment. The multi-electrode sources array resistivity method can reflect the presence of abnormal body and it is consistent with the actual model. The detection distance can reach 30 m and its vertical resolution can reach 2 m with existing model parameters. It shows the effectiveness of this method and the interpretation accuracy for water-bearing structure is improved.Based on the multi-electrode sources array resistivity method, the advanced detection for water-bearing structures 30 m ahead of tunnel face can be achieved. In addition, the resistivity method plays an important role in water-bearing structures' advanced detection and the prevention of water inrush disaster. So, further research should be taken urgently in the fields such as the advanced detection mechanism of resistivity method, inversion interpretation, computational efficiency, and the increase of effective observation data. Besides, the 3D parallel inversion, large proportion model experiment and project verification should also be carried out.