Study On The Breaking And Control Of Key Strata Under Short-Wall Mining In Shallow Seam

How to realize the stable yield of pillar left in the panel between branch entry through the rational project design, and then relieve or eliminate the dynamic disaster caused by the hard roof caving under shallow depth, meanwhile maximize the coal recovery are very important for application of short-wall mining technology and maximize the corner coal recovery in Shendong mines. This dissertation comprehensively utilizes the theoretical analysis, physical modeling, numerical simulation methods to analyze the deformation and energy distribution before cracking and the stable mechanism of voussoir beam structure after cracking of the key strata that determines the stabilization of roof in shallow seam, and further study the deformation and cracking law of key strata above the two adjacent panels when one of them is being mined, and optimize the engineering design plans of “key strata-yield pillar” system safe failure.The main innovative points are listed as follows:(1) This dissertation estabilishes the compound foundations beam model with consideration of coal rib yield zone to analyze the relationship between yield zone width and the first cracking, periodic cracking of key strata, and the cracking position, energy distribution and deformation distribution. The criterion and calculation methods for voussoir beam under the action of original horizontal stress, and the cracking process, deformation, stress distribution and caving mechanism of key strata and other roofs above it have been systematically researched.(2) According to the characteristics of panel layouts of short-wall continuous mining, this dissertation studies the influence of adjacent panel mining to key strata stabilization above them. The relavent results show that the the recovery of the mining panel can increae the deformation of key strata above the adjacent mined out panel seriously, especially when the mined out panel's size is large, and meanwhile the key strata stabilization above the mined out pan can determine the deformation, maximum span and caving mode of key strata above adjacent mining panel, those influence can be explained through the two compression arches interaction above two panels.(3) This dissertation proposes a theory of “key strata-yield pillar” safe failure based on the yield pillar theory and the local masses stiffness theory after improving its calculating methods, and simplifies the yield pillar design plans into six foundamental stiffness nuits under systematically research on the effects of branch entry width, branch entry mining sequence, the position of last mined branch entry in panel, the position and number of yield pillar(between two branch entries) to local masses stiffnes, and determine the rational yield pillar width corresponding to each local stiffness unit, and optimize the yield pillar design plans through comprehensive considerations of the safe mining of the last branch entry in the panel, key strata safe failure, increasing recovery area and recovery ratio in one panel, and further give the flowchart of engineering plan optimization design for “key strata-yield pillar” system safe failure.