Different coal pillar widths result in the differences of deformation, stress and movement of rocks surrounding gateway and importantly influence on the stability and maintenance of gateway. According to the geological and mining technical conditions of the No. 1151 (3) fully mechanized top-coal caving (FMTC) mining face in Xieqiao Mine and based on the analysis of numerical simulation, the characteristics of deformation, stress and movement of rocks surrounding gateway and the stability of gateway is integratedly investigated. The results show that the stress distribution laws and deformation characteristics of gateway surrounding rocks are obvious diversity with different coal pillar widths during caving. And stress distribution of coal pillar and coal entity is displaced with different wide pillars. The deformation and stability of gateway is determined on the stress distribution and its development of coal entity and coal pillar and appropriate width of coal pillar is less than the critical displacing stress-width. These would provide the theoretical basis for the rational setting of the coal pillar width, gateway laying, support parameter selection, stability control of the gateway surrounding rock of the mining gateway and for the safe and economic production etc.
Based on the 3-D stress fields of working face and surrounding rocks, the changing of coal pillar width results in not only the mechanic state of coal pillar changing, but also the mechanic field of coal entity besides of pillar changing. The changing laws certainly will influence the stability of gateway [1~4]. FLAC3D is widely applied in simulating and computing geological materials and rock-soil engineering with nonlinear, big-deformation and instability mechanic actions, especially in plastic flow after yield and gradual breaking and falling [5~7]. So the surrounding rocks fracturing and stress fields of gateway are simulated and analyzed with FLAC3D in different wide pillars and surrounding rocks stability of gateway influenced different coal pillar widths is discussed.
The length on the strike is 1674m and to the dip is 231.8m, the ground level is +20.4~+25.8m and the face level is -588~-662m of the No. 1151 (3) fully mechanized top-coal caving (FMTC) mining face in Xieqiao Mine. The coal seam texture is steady, the average thickness of coal seam is 5.4m, the average obliquity is 13°, the ratio of caving height and top coal height is 1:1~1.08. The conditions of seam roof and floor are: main roof is powder and thin sandstone, thickness is 6.2m; immediate roof is slob or arenaceous slob and C13–2, thickness is 3.26m; immediate floor is slob, thickness is 1.5m; main floor is powder sandstone, thickness is 2.8m.
In order to estimating rocks breaking, reflecting remains strength gradually reducing during deforming and gob rock-debris perdurable bulk contractility and strain induration, the mohrcoulomb yield criterion(formula (1)), strainintenerate model and bulk-induration are respectively applied.