Study On The Depressurization Effect Produced By Exploitation Of Lower Protective Coal Seam

Practice shows that gas extraction during protective coal seam mining is one of the most effective measures against of coal and gas outburst; and strata conditions are closely related with protected seam pressure relief affects. In this thesis, aim at three kinds of overburden strata model, using numerical simulation software UDEC research on the influences of different factors, such as interlayer spacing, interlayer lithology, interlayer key stratum position, thickness of key stratum and distance fracture of key stratum on the pressure relief mining of low protective coal seam, the study concluded that:(1) With the increase of interlayer space, the expansion rate and pressure relief coefficient increase.(2) With the interlayer rock hardness increase, the pressure relief starting distance increases; the expansion rate and expansion interval has increased.(3) the closer the distance between protected coal seam and interlayer key stratum is, the larger fracture spacing is, the less apparent protected seam development is, the worse effect of pressure relief are.(4) The thicker the key stratum above protected seam is, the large fracture spacing is, the large characteristics parameters of pressure relief in the protected seam are, he better pressure relief effects and desorption with gas are.Based on the same spacing and displacement vector fields of the overburden in stope, the characteristics of displacement field and stress field evolution, fracture field, temporal and spatial distribution before and after fracture of key strata were studied, the study concluded that:(1) Three models of stress partition and expansion partition along the strike division is the same, but the width and time of each interval is different, that has obvious space-time effect;(2) The motion rule of mining-induced overburden rock, the dynamic evolution and distributions of the overburden bed separations and fractures, and stress changes and the deformation of protected coal seam have been controlled by the positions and fracture distance.The conclusions provide theory foundation to protective coal seam mining against of coal and gas outburst.