Tectonic Motion And Control Of Overburden In Thin Bedrock Fully-mechanized Sublevel Caving Face

In Lu’an coal field which is characterized by rich coal resource with thin overlyingrock mass, working face stents failure accidents caused by ground pressure oftenhappened during the past mining practices, therefore, it is quite necessary tosystematically study the overlying rock mass movement rule under this geologicalcondition to make this coal resource mine safely and efficiently. In this paper, we takeSima coal mine in Lu’an coal field as the research base, and in view the geologicalcondition of thin overlying rock, thick loose bed and coal seam in this coal mine, carryout deep investigation on the overlying rock mass movement rule and stents-surroundingrock mass relationship by systematically applying theoretical analysis, numericalsimulation, physical simulation and practical measurement, obtaining the followinginnovative achievements:(1) We build a structural mechanical model for thin overlying rock mass with thickloose bed under condition of fully mechanized mining, and revealed the formation ofcomposite beam-arch balance structure as well as the mechanical mechanism that theroof will be hard to happen periodic failure under this geological condition, then weproposed the stability criterion condition for this composite structure.(2) Hyperbolic relationship between supporting force P and roof subsidencedistance lcan still be satisfied under fully mechanized mining with thin overlyingrock mass, so increasing the stent working force and effectively control the roofsubsidence distance. Furthermore, we obtained the relationship between stent supportforce, roof subsidence deformation and lithology, thickness of rock, and revealed thestent-surrounding rock interaction relationship, which can provide theoretical basis forstent choose when mining with thin overlying rock mass.(3) We obtained the ground pressure appearance character under fully mechanizedmining with thin overlying rock mass and thick loose bed according to the research inLu’an coal seam, that is to say, both the first weighting distance, and periodic weightingdistance are small, roof subsidence velocity was large, and ground pressure ischaracterized by shorter weighting distance, larger static pressure, smaller dynamicpressure and dynamic load coefficient. This study can provide basis for ground pressureprediction and roof management under fully mechanized mining with thin overlying rockmass and thick loose bed(4) According to the structural characteristic and load transfer property of overlying rock mass under condition of thin overlying rock with thick loose bed, we defined rockmass which have characteristics include small thickness, less evident ground pressureand stent bear load from weight of rock and clay in arch as super thin rock mass. Whilefor rock mass which have property that voussoir beam structure can form after the keyrock strata failed, ground pressure is obvious with weak strength, and stent bear loadcased by subsidence deformation of voussoir beam and weight of rock below key rockstrata, we classified this type of rock as thin rock mass. Furthermore, we proposed thecorresponding mining scheme and choose principle.The research results have been successfully applied in mining practice Sima coalmine with thin overlying rock mass, and can provide theoretical study and reference ofother coal mine under this similar geological condition.