Formation mechanisms and modes of karst collapse columns based on multi-information exploration technology: a case study of Fengpei coalfield, North China

Abstract Backgrounds Karst collapse columns (KCCs) are widely developed geological structures in the North China Coalfields and represent one of the primary factors contributing to mine water inrush hazards. Methods In this study, a multi-information exploration technology was established by integrating geophysical surveys, drilling, underground roadway exposure, scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and water injection testing of column structures. This methodology was applied to characterize the features and formation mechanisms of KCCs in the Fengpei coalfield (Jiangsu Province, China). Results Furthermore, the study proposed formation modes of KCCs, examined the impacts of mining and grouting activities, and developed a low-disturbance grouting treatment method. The results show that (1) the filling of KCCs primarily consist of clay minerals, which account for 38–78.8% of the total composition. Most KCCs exhibit low calcite content and good cementation, predominantly characterized by argillaceous cementation; (2) the KCCs in the Fengpei coalfield are paleo-KCCs formed under the combined control of thick-bedded Ordovician limestone lithology, regional tectonics, favorable hydraulic connectivity, and high-temperature corrosive water. These KCCs are predominantly in a declining or inactive stage, with permeability ranging from 0.4 to 0.5 Lu, indicating low water abundance and hydraulic conductivity; (3) four formation modes of KCCs were identified: Karst strong runoff zone control mode, Fold structure control mode, Fault structure control mode, and High-temperature corrosive water control mode, which were further subdivided into six subcategories; (4) a low-disturbance grouting treatment method for KCCs was developed. This method prioritizes grouting within the fractured zone of the roof above the mining panel, outside the mining-induced damaged zone in the floor, and within the primary water-bearing thin limestone layers of the Taiyuan Formation and its roof, located beneath the main coal seam. The grouting forms a “water-blocking plug” with a thickness exceeding the safe water-barrier thickness of the mining panel. The permeable rate of KCCs was reduced to 0.21–0.36 Lu after grouting, effectively eliminating their impact on coal seam mining. Conclusions It can provide a basis for accurate exploration, spatial distribution prediction, and subsequent treatment of KCCs in coalfields.