Overlying Strata Movement Laws And Ground Control Of The Longwall Face Mining In A Shallow Depth Seam In Proximity Beneath A Room Mining Goaf

According to the geological conditions of the longwall face mining in theshallow depth coal seam in proximity beneath a room mining goaf in the ShendongCoal Field, in situ survey, numerical simulation, physical simulation, theoreticalanalysis and field experiment were undertaken to study the stability of the roommining goaf residual coal pillars, the large area roof weighting mechanism and itscontrol technology, overlying strata movement laws and ground control of thelongwall face, the major achivements are as follows:(1) The instability mechanism of the room mining residual coal pillars wasuncovered by the integrate analysis of gradually damage theory and catastrophe theory,and the criterion of pillar instability was also established. The room mining residualcoal pillars instability was calculated with gradually damage theory, and the pillardesign size, which meet the request that safety factor greater than1.5, was judgedaccordingly. The cusp catastrophic model was established through catastrophe theory,and an essential condition to indicate pillar mutation was presented as0.33w<Y<0.43w, i.e. the pillar cannot occur mutation instability if the elastic areawidth greater than34%of the total pillar width, this result is consistent with the in situobservations, thence the instability mechanism of the room mining residual pillarswas uncovered.(2) The overlying strata movement structure model of the longwall face miningin the shallow depth seam beneath a roof mining goaf was set up, and the reasonablesupport working resistance was also confirmed. Based on the theory of ElasticMechanics, a clamped beam and a cantilever beam were built to analyze the roofweighting length, and the tensile yield and shear yield of the mian roof werecompared, then the first roof weighting length and the period weighting length werecalculated and monitored. According to the overlying strata movement characteristicsof the longwall face mining in the shallow depth coal seam in proximity beneath aroom mining goaf, the system of “Loading layer-Main roof-Room mining residualpillar-Immediate roof-Support” can be divided into two linking systems including“Loading layer-Main roof-Room mining residual pillar” and “Room mining residualpillar-Immediate roof-Support”, and then the reasonable support working resistancecan be achieved. Furthermore, the slice-caving criterion of the immediate roof wasrevealed through the mechanical equilibrium analysis of the immediate roof structure. (3) The mechanism of the deep-hole pre-split blasting for controlled roof cavingwas uncovered, and the application avoided the large area roof weighting accidents. Alarge area roof weighting wind blast model was established to explain the wind blastinduced fully mechanized equipment damage and roadway destroy. To prevent largearea roof weighting, a deep-hole pre-split blasting technology carried out at theopen-off cut for controlled roof caving was presented, the software of LS-DYNA3Dwas used to set up a simulation model, then the mechanism was revealed and themajor blasting parameters were also optimized. The field experiment indicated thatthis technology was successfully practiced for controlled roof caving.(4) The roof control technologies including control the reasonable mining heightand increase the mining speed properly, etc. were presented to enable the achievementof safe and highly-efficient mining in the shallow depth seam in proximity beneath aroom mining goaf. According to the overlying strata movement laws of the longwallface mining he shallow depth seam in proximity beneath a room mining goaf, the roofcontrol technologies including control reasonable mining height, sandfilling in theroom mining goaf, enhance the roof control management and increase the miningspeed properly were presented, and the in situ experiments enable the longwall facemining safely and efficiently.