Detection of coal seam floor failure depth through borehole direct current resistivity monitoring

Accurately monitoring mining-induced floor failure depth during coal seam extraction remains a critical technical challenge for preventing water inrush disasters. To address the limitations of existing methods—including low efficiency in borehole observation and insufficient resolution in geophysical detection—this study proposes a floor failure depth monitoring technique based on the borehole direct current (DC) electrical method. By deploying electrodes within boreholes, this approach directly acquires high-resolution resistivity profiles along vertical sections. Numerical simulations were first conducted to reveal the dynamic evolution patterns of apparent resistivity in mining-disturbed floor failure zones. Subsequently, field implementation at a typical coal mine demonstrated the methodology‘s effectiveness through monitoring electrical property variations in floor strata during pre-mining, active mining, and post-mining stages. Key quantitative results include: an identified floor failure depth of 27 m, a fracture angle of 50°, and a clear correlation with the 35 m roof caving interval. Under the layered geological model with an electrode spacing of 2 m and a borehole dip angle of 30° as set in this study, the depth identification accuracy of the variation-rate method is improved by 40–60% compared with conventional apparent resistivity imaging, which can serve as a reliable risk assessment tool for water inrush prevention in deep mining operations.