Theoretical foundation of tensor measurement for mine resistivity method

The law of temporal and spatial evolution of local or microscopic anisotropy,caused by coal mining,is a key study on coal mine dynamic disaster prediction and prevention. As an important approach to understand the anisotropic characteristics of coal and rock mass,the tensor resistivity measurement has unique advantage in underground mine roadway. Based on the analysis of physical mechanism for rock resistivity anisotropy along with underground roadway circumstances,a mine tensor resistivity method was proposed. Taking the examples of anisotropic layered medium models,the apparent resistivity was calculated with different stratigraphic dips and strikes,and the directional characteristics of which were analyzed. Using a full-space model with Karst development,the directionality of mine resistivity method was analyzed and verified from global anisotropic response view. The results show that it has an anisotropic behavior in coal and rock mass under the influence of mining,and the water-gas enrichment status in fracture has an effect on the horizontal and vertical resistivities. The anisotropic coefficient increases with water content. Apparent resistivity amplitude in an anisotropic stratum is affected by its overlying and underlying strata,which reflects a comprehensive response of all layers. Besides,the amplitude can be decided by the fracture zone dips instead of the strikes,however,the elliptic resistivity distribution rotates owing to the strikes change. The results also indicate that the regular temporal and spatial evolution of strata anisotropic behavior is influenced by rock mass deformation and failure,as well as fluid migration. By real-time dynamically measuring the tensor resistivity of coal and rock mass,the local or microscopic anisotropic characteristics caused by mining and fluid migration can be recognized. Capturing auspice signal containing dynamic disaster gestation and development in time before the peak stress arrives,and adopting prevention approach in reversible phase before stress releases,the significant dynamic disasters can be avoided from the source.