METHOD OF MINING HEAVY COAL SEAMS IN TWO OR MORE BENCHES

In mining a heavy coal seam that must be excavated in several benches, the excavation of the uppermost bench is accompanied by the introduction of a cementitious slurry into the resulting stope for consolidating the waste rock present therein, preparatorily to the excavation of the next-lower bench, and proceeding in like manner with the second bench if a third one is to follow. The cementitious slurry comprises burnt or slaked lime, and/or portland cement, suspended in water in a quantity of about 10 to 60 % by weight and preferably together with a small percentage of chlorides of one or more alkali or alkaline -earth metals, to which ceramic aggregates of large specific surface such as mineral ashes, slag, sand or dolomite powder may be added in a quantity of up to about 30 % of the weight of the water. The slurry, on being admitted to the stope in an amount of at least 10 % of the volume thereof, causes the waste rock to swell and to form a solid layer of up to approximately a meter in thickness which allows the next-lower bench to be excavated after only about a month's delay.