Research On Stability Of Overlying Strata And Reasonable Waterproof Coal Pillar With Backfilling Mining In Steep Seam Under Water Body

The overlying strata are liable to damage and water flowing fractures develop upwardwhen steep seam is mined. Meanwhile, waterproof coal (rock) pillar will fall and produceplastic zone under the water head pressure and ground pressure. Thus, there is safety miningincipient fault under water body in steep seam. Backfilling mining is efficient measure tomine coal resource under the water body. Therefore, the key technology research that waterinrush prevention and control for backfilling mining is of prominent theoretical and practicalmeaning for safety and efficient mining under the water body in steep seam.The dispersed element numerical calculation as well as similar simulation experimentwas applied to study the influence of structure key stratum, resisting key stratum and theirstructure combination of overlying strata on breakage characteristic of overlying strata andwater flowing fracture evolution in steep seam. The results show that while there is not keystratum in overlying strata and structure combination of overlying strata is resisting-structurekey stratum, water flowing fracture mainly presents "ear style" distribution; while there is keystratum in overlying strata and structure combination of overlying strata is structure-resistingkey stratum, water flowing fracture mainly produce bed separation fracture parallel to thebedding face; first breakage of hard roof would have great influence on strata pressurebehavior law and water flowing fracture evolution. Meanwhile, backfilling mining in steepseam can effectively reduce the motion trend of stope surrounding rock to free surface andwater flowing fracture distribution decreases with the increment of backfilling range andbackfilling body strength.According to stress distribution state of the roof rock beams, roof control mechanicalmodel was built for backfilling mining in steep seam. The results indicate that backfillingmining can effectively prevent tension failure, shear breakage and shear-slip failure as well asdecrease bending flexivity of roof beam in steep seam. At the same time, backfilling miningcan reduce stress concentration degree and falling range of waterproof pillar as well asunloading zone, abutment pressure zone and of floor strata deformation. Hereby, strata controlmechanism around coal face for backfilling mining was put forward in steep seam underwater body.Consideration of the influence of original horizontal stress, based on boundaryconditions and stress characteristic of waterproof pillar, reasonable waterproof pillar size wasobtained by theoretical analysis under the water body in steep seam. The results by fluid-solid coupling numerical calculation show that the falling range of waterproof pillar would beincreased in tendency with the coal thickness and reduction of coal body strength; structurekey stratum occurred in overlying strata and breakage revolution of immediate roof wouldlead to the increment of waterproof pillar falling range. Meanwhile, shear-slip fracture causedby tangential stress concentration in the position of waterproof pillar floor is the major waterinrush way into the coal mine. Besides, compound waterproof isolation strip for "ganguebackfilling zone+waterproof pillar" which worked-out section is backfilled by gangue aswell as grouting cementation in steep seam can effectively prevent water inrush accidentunder large mining range condition.Based on the occurrence conditions of steep seam and hydrological engineeringgeological conditions in South No.2District of Longhu coal mine, appropriate mining methodis studied and the technology that worked-out section is backfilled by gangue as well asgrouting cementation is designed to control roof stability and ensure the safety mining underwater body in steep seam. The result shows that the backfilling technology has better effectand gains remarkable social and economic benefits.The research results in the dissertation not only offer safety and reliability guarantee forbackfilling mining under the water body in steep seam, but enrich backfilling mining theory.