Mechanics Evolution Characteristics And Instability Mechanism Analysis Of The Pressure-arch In Mining Field

With the underground coal mining out, it will generate within a certain range in thesurrounding rock, which forms the pressure-arch in the mining field. The pressure-archcan sustain its loading and transfer the other loads to the foot of the pressure-arch, and thisis of great significance to ensure the stability of the surrounding rock of the mining field.Therefore, it has an extremely important theoretical and practical value to study theevolution of the pressure-arch in mining field and its characteristics of instability.Based on a mining area of Fangezhuang Coal Mining, using theoretical analysis andthe FLAC3D, this paper has researched the mechanics evolution characteristics analysis ofthe pressure-arch in mining field and distribution characteristics analysis of thepressure-arch in horizontal stratified rock during the coal mining and instabilitymechanism of the pressure-arch in mining field, and some results of the actualconstruction of the guiding significance have been obtained as followed:Firstly, based on a practical engineering, the three-dimension computational modelwas built using FLAC3Dunder the fully-mechanized mining condition. Considering fourvariation factors, such as the distance of mining advancing, the strength of the surroundingrock, the speed of mining advancing and the dip angle of the coal seam, the mechanicsevolution characteristics of the pressure-arch were analyzed. The result illustrated that forthe horizontal seam, the geometric shape of the pressure-arch varied from flat arch torounded arch gradually, the height and thickness of the pressure-arch increased, and themaximum principal stress in the skewback increased also with the working face advancing.With the strength of the surrounding rock from soft to hard, the arch thickness reduced,and the arch loading decreased. To improve the mining speed can do some contributions tothe stability of the pressure-arch in the mining field. With the dip angle of the seamincreasing, the pressure-arch displayed asymmetric shape; the vault was tilted and movedto the upward direction. At the same time, the thickness of the pressure-arch increased,and the stress concentration in the skewback tended to be further intensified.Secondly, Considering five variation factors, such as the number of layers, the distance from weak interlayer to mining field, the thickness of weak interlayer, the lateralpressure coefficient and the spacing of the bedding plane, the distribution characteristicsof the pressure-arch in horizontal stratified rock were analyzed during coal mining byusing FLAC3Dtechnique. The results showed that the new pressure-arch would becomposed by original pressure-arches in each layer and the weak layer affected the shapeof the pressure-arch in the surrounding rock of the mining field. With the distanceincreasing between the interlayer and the coal seam, the effects reduced. The thinnerinterlayer would produce the greater impact on the surrounding rock. The lateral pressurecoefficient had a great influence on the pressure-arch, and only the suitable lateral pressurecoefficient could form a stable pressure-arch. The more small spacing of the bedding planewould have the greater influence on the pressure-arch.Finally, the pressure-arch structure mechanics model was built. There are three formsof failure models: tension-failure shear-failure and compression-failure. With the increaseof dip angle of the seam, the instability modes of the pressure-arch change fromcompression-failure at the arch-waist and shear-failure at the skewbacks to shear-failure atthe vault and tension-failure at the front skewback.