Water and Sand Inrush During Mining Under Thick Unconsolidated Layers and Thin Bedrock in the Zhaogu No. 1 Coal Mine, China

摘要

Raising the upper boundary of coal mining under thick Cenozoic unconsolidated layers has brought new challenges to the prediction and prevention of water and sand inrush from overlying sand and gravel aquifers in north China. The mechanism of water and sand inrush was studied based on an incident that occurred at working face 11071 in the Zhaogu No. 1 coal mine, in Henan Province. Geological and hydrogeological investigations in overlying strata indicated that intersections of horizontal confined aquifers and inclined bedrock surfaces, defined as skylight areas, allow water and sand from the aquifers to enter the workings. Geotechnical and physical simulation tests on overlying strata showed that mining-induced fractures in weathered bedrock were gradually enhanced by water and sand flowing under high pressure, leading to inrush incidents at the working faces. The empirical formula for estimating the requisite size of coal and rock pillars were modified by incorporating a term for protective thickness under skylight areas. The modified formula was successfully applied to the extraction of neighboring faces, proving its applicability in coal mines with similar geological and hydrogeological conditions.