Asymmetrically focused DC resistivity-based detection method of water-saturated cross-shaft fracture

Accurate detection and then in-situ monitoring of cross-shaft water-saturated fractures are critical for obtaining essential data to advance lining-based disaster prevention theories. These capabilities are particularly significant for addressing geology challenges in shaft design, construction, and operation in Western China. Despite their importance, studies in this field remain limited, highlighting a need for further investigation. To address these challenges, we developed an innovative asymmetrically focused direct current (AFDC) -based method. Through comprehensive numerical simulations and model experiments incorporating freezing pipes, we characterized AFDC resistivity behavior under cross-pipe mode (CPM) and compared it with symmetrically focused direct current (FDC) resistivity. The results showed that both the AFDC and FDC resistivities increased as fracture width w decreased and offset distance d relative to left freezing pipe increased. The maximum horizontal propagation radius d max of the detection current increased as emitting and receiving electrodes spacing increased under single-pipe mode (SPM). Parameters d and w can be determined with an error <10 % by initially obtaining d = d max correspondent to FDC resistivity drop under SPM and afterwards obtaining w using a simplified equation correlating d and dimensionless AFDC or FDC resistivity under CPM. The developed AFDC-based method leverages freezing pipes, offering operational simplicity, cost-effectiveness and reliable detection and then real-time monitoring of water-saturated cross-shaft fracture.