Prevention of sudden rock movements in coal mining - by stress-releasing injection of aq. salt solns. e.g. of calcium chloride and nonionic wetting agent

摘要

Sudden rock movements in coal mining are prevented by injecting the coal seams with aq. salt solns. through boreholes driven from outside the coal extraction area, from seams above or below that being worked or from independent mine workings. Pref. the soln. used contains 30-40 wt.% CaCl2 and/or MgCl2 and 0.2-0.5% non-ionic wetting agent. Stresses in the rock layers can be released without interfering with coal extraction. Coal pillars left to prevent subsidence can be treated. The good wetting action of the salt soln. used allows injection under relatively low pressure and prevents escape into adjacent rock formations or breaking up of the coal.