Development Range Determination of Gas Conducting Fissure Zones for Lower Protective Seam Mining in JINJIA Coal Mine

Under the circumstance that lower protective seam mining may give rise to mining-induced fracture development in the upper coal and rock mass, the key to gas extraction during lower protective seam mining is investigated based on mining-induced fracture development law of overlying strata. Fracture evolution processes are seldom described by the traditional “Three Zone” theory of overlying strata. Consequently, its field application in gas extraction during the lower protective seam mining is limited. While theoretical analysis and analog simulation are adopted to analyze mining-induced fracture development rules for the lower protective seam mining, a plastic hinge is selected to theoretically derive a process from internal fracture development to occurrence of rock beam fracturing. In combination with the theory of key strata that the movement of overburden is controlled by key bond strata, a computing method is obtained to figure out development height of a gas conducting fissure zone during the lower protective seam mining. Taking geological conditions in Jinjia Coal Mine as the engineering background, development height of the gas conducting fissure zone in No. 22 seam there is calculated to be 42.2 m. On this basis, engineering design is performed for pressure relief gas extraction of the lower protective seam mining. During working face mining, gas emission quantity and sources are also monitored according to gas conducting features of strata within a range of the gas conducting fissure zone. Hence, accuracy in development range computations for this zone is verified. As demonstrated by research findings, combining the plastic hinge theory with a control action of key strata has the potential to effectively work out development height of the gas conducting fissure zone during the lower protective seam mining. Without a doubt, an accurate theoretical basis can be provided for pressure relief gas extraction in the course of lower protective seam mining.