Technique of coal mining and gas extraction without coal pillar in multi-seam with low permeability

Abstract

Aimed at the low mining efficiency in deep multi-seams because of high crustal stress, high gas content, low permeability, the compound “three soft” roof and the troublesome safety situation encountered in deep level coal exploitation, proposed a new idea of gob-side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction. The following were discovered: the dynamic evolution law of the crannies in the roof is influenced by mining, the formative rule of “the vertical cranny-abundant area” along the gob-side, the distribution of air pressure field in the gob, and the flowing rule of pressure-relieved gas in a Y-style ventilation system. The study also established a theoretic basis for a new mining method of coal mining and gas extraction which is used to extract the pressure-relieved gas by roadway retaining boreholes instead of roadway boreholes. Studied and resolved many difficult key problems, such as, fast roadway retaining at the gob-side without a coalpillar, Y-style ventilation and extraction of pressure-relieved gas by roadway retaining boreholes, and so on. The study innovated and integrated a whole set of technical systems for coal and pressure relief gas extraction. The method of the pressure-relieved gas extraction by roadway retaining had been successfully applied in 6 typical working faces in the Huainan and Huaibei mining areas. The research can provide a scientific and reliable technical support and a demonstration for coal mining and gas extraction in gaseous deep multi-seams with low permeability.