The Joint Exploration Of Ground-tunnel Resistivity Method

In recent years,the rapid growth of infrastructure such as cities,highways and railways across the country,and the frequent occurrence of geological disasters in subway and tunnel construction,requires improving the detection accuracy of disaster-causing structures,fissures,caves and other undesirable geological bodies around underground tunnels.Due to the attenuation characteristics of the observation field,traditional ground geophysical exploration often has high shallow resolution,and the deeper the resolution,the lower the resolution,and even the limited detection and identification of local adverse geological bodies around deep alleys(tunnels)can not be carried out.However,the environment and working space in the tunnel are limited,which restricts the development of geophysical methods,if the groundtunnel joint geophysical exploration technology is carried out,it not only makes full use of the favorable working conditions of the ground,but also uses the tunnel observation to approach the key detection area as much as possible,in order to improve the detection effect of the tunnel periphery.In this paper,the ground-tunnel joint detection of resistivity method is taken as the research object,and the forward and inverse technology of tunnel resistivity method is studied.Firstly,starting from the differential equation satisfied by the three-dimensional point source field in the whole space,the edge value problem of the potential satisfied in the stable current field is given.Aiming at the detection task of three-dimensional tunnel resistivity method,a grid segmentation technology centered on tunnel is established,the finite element forward algorithm of tunnel resistivity method is derived,and the forward evolution program is compiled.In order to improve the forward efficiency,the MSR non-zero element compression technology is adopted to save the storage consumption of the coefficient matrix of the equation system,and the SSOR-PCG iterative method is used to solve the solution to improve the calculation speed of the 3D forward evolution,and realize the 3D fast forward evolution of the tunnel resistivity method.On the basis of the forward evolution,through the model forward evolution,the influence of the tunnel itself on the observation of the tunnel resistivity method is analyzed and discussed,and the influence law of the measurement line at different positions in the tunnel is analyzed,and the quantitative correction formula of the influence of the tunnel itself on the resistivity method observation is established.The influence of anomalies above,below and side of the tunnel on the detection by resistivity method was discussed,and the anomaly characteristics of the ground-tunnel combined resistivity method detection were discussed.Aiming at the ground-tunnel joint detection,the ground-tunnel apparent resistivity approximation imaging technology and the optimized least squares inversion algorithm are discussed in detail.The inversion results of the combined data and measured data of the model show that the ground-tunnel combined resistivity method detection can realize the high-precision detection and inversion interpretation between the ground-tunnel.