3D E-SCAN resistivity inversion and optimized method in tunnel advanced prediction

Advanced geological prediction is one essential part in tunnel construction, and 3D E-SCAN resistivity device is introduced. In this device, the current and measuring electrodes are arranged on the tunnel face, which can reduce the impact of interference factors. Then a new observing device is proposed. Geological models are designed, and features of the sensitivity matrix are obtained as follows: the absolute values of elements are vastly different; the values decrease sharply with depth; the elements close to the current and measuring electrodes achieve high absolute values. The gain factors with different values are imposed onto the elements in the sensitivity matrix, and the initial elements with high values are suppressed, with the elements with low values enhanced. An optimized inverse method is formed based on the gain factors, and it can promote the depth accuracy of the abnormal in inverse results theoretically. Numerical examples and physical model tests are performed. The results show that in the 3D E-SCAN resistivity detection, compared with the traditional smooth constraints inversion, the optimized inverse method has obvious advantages in positioning the abnormal body in depth.