A study of mine water inrushes by measurements of in situ stress and rock failures

This paper presents underground measurements (e.g., mini-frac tests) for in situ stress, hydraulic fractures, strata failures and hydraulic conductivity enhancement induced by coal extraction to study mechanisms of coal mine water inrushes. Mining perturbs the original state of in situ stress and results in stress redistribution. This causes rock failures and creates a water-conducting failure zone around a mining panel. If a confined aquifer is situated in the coal seam floor, the mining-induced stresses near the aquifer also generate hydraulic fractures in the rocks near to the aquifer. The mining-induced water-conducting failures and hydraulic fractures by the water pressure of the aquifer are the major reasons to cause water inrushes. The mining-induced water-conducting zone is obtained from theoretical studies and field measurements. The generating condition of the hydraulic fractures by the water pressure is also studied. Methods for predicting water inrushes are given based on the study of water inrush mechanisms. The mechanisms of water inrushes induced by faults are also analyzed from the case studies of water inrushes. It is of crucial importance to detect and map faults, paleo-sinkhole and other geological structures before mining. New mining methods are proposed for mining near confined aquifers to reduce the risks of water inrushes.