Publication Date
April 2018
Abstract
Coal mining in China has exposed numerous karst collapse columns of tens of meters in diameter and hundreds of meters in height. Hydraulically conductive collapses have functioned as groundwater pathways between the underground workings and the aquifers, resulting in water inrushes during coal mining. Over the last 40 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment. Two such collapse features were unexpectedly encountered during operations in Renlou Coal Mine of China. The first encounter caused flooding of the entire mine. Although no serious damages occurred at the second encounter, because of timely and effective grouting measures, the production rate was reduced. Proactive detection of any concealed karst collapses and determination of their hydrogeological characteristics were essential components of a comprehensive investigation program in preventing water inrush incidents and ensuring normal coal production in the mine. The investigation program included surface and underground geophysical surveys with five geophysical techniques and directional drilling of three exploratory boreholes at completion depths ranging from 902 to 986 m. A new collapse feature was identified through systematic analysis of the data collected in the investigation program. Although the bottom of the collapse feature has not been determined, its total height is more than 135 m. The roof was at approximately 785 m depth, and there was an open void 1.5 - 2 m high at the top. Geotechnical properties, results from packer testing and tracer testing, monitoring of potentiometric pressures, and geochemical fingerprinting suggested that this collapse column was hydraulically conductive and still actively developing. Water in the confined thin-bedded limestone and Ordovician limestone aquifer that either overlies or underlie coal seams could flow into the mining areas if this feature were not identified in advance but encountered during mining. A grouting program was designed and implemented to construct a water plug in the collapse that effectively cut off the hydraulic connections from the aquifers to underground workings. Successful construction of the water plug in the collapse was confirmed by water intake tests in the grouting holes, water flow measurements in the mining area, and groundwater level monitoring in the aquifer.
DOI
https://doi.org/10.5038/9780991000982.1048
Comprehensive Investigation and Remediation of Concealed Karst Collapse Columns in Renlou Coal Mine, China
Coal mining in China has exposed numerous karst collapse columns of tens of meters in diameter and hundreds of meters in height. Hydraulically conductive collapses have functioned as groundwater pathways between the underground workings and the aquifers, resulting in water inrushes during coal mining. Over the last 40 years, water inrushes through these collapses have caused fatalities, economic losses, and degradation in the environment. Two such collapse features were unexpectedly encountered during operations in Renlou Coal Mine of China. The first encounter caused flooding of the entire mine. Although no serious damages occurred at the second encounter, because of timely and effective grouting measures, the production rate was reduced. Proactive detection of any concealed karst collapses and determination of their hydrogeological characteristics were essential components of a comprehensive investigation program in preventing water inrush incidents and ensuring normal coal production in the mine. The investigation program included surface and underground geophysical surveys with five geophysical techniques and directional drilling of three exploratory boreholes at completion depths ranging from 902 to 986 m. A new collapse feature was identified through systematic analysis of the data collected in the investigation program. Although the bottom of the collapse feature has not been determined, its total height is more than 135 m. The roof was at approximately 785 m depth, and there was an open void 1.5 - 2 m high at the top. Geotechnical properties, results from packer testing and tracer testing, monitoring of potentiometric pressures, and geochemical fingerprinting suggested that this collapse column was hydraulically conductive and still actively developing. Water in the confined thin-bedded limestone and Ordovician limestone aquifer that either overlies or underlie coal seams could flow into the mining areas if this feature were not identified in advance but encountered during mining. A grouting program was designed and implemented to construct a water plug in the collapse that effectively cut off the hydraulic connections from the aquifers to underground workings. Successful construction of the water plug in the collapse was confirmed by water intake tests in the grouting holes, water flow measurements in the mining area, and groundwater level monitoring in the aquifer.
