Optimization of staggered distance of coal pillars in multiseam mining: Theoretical analysis and numerical simulation

Abstract

Aimed at solving problems related to water retention and loss reduction in multiseam mining, a mechanical model of staggered distance mining was established. First, elastic and plastic slip line field theories were used to calculate the reasonable staggered distance expressions of multiseam mining. The staggered distance schemes of multiseam mining were optimized using the numerical simulation software FLAC3D. By performing an experiment comparing similar materials, the influence on water retention and loss reduction by optimal and unfavorable staggered distance schemes in multiseam mining was explored. The results showed that the σzz curve was distributed in the shape of a “peak” of the staggering distance coal pillars, the Z displacement curve was a “Л,” and the surface subsidence curve was a “W.” Each of these displayed the rule of “decrease then increase.” In staggered distance multiseam mining, the optimal staggered distance value for coal seam Nos. 2 and 3 was 40 m, while the most unfavorable staggered distance value was 0 m. The corresponding subsidence coefficients of the optimal staggered distance values were 0.29, 0.23, and 0.19, under the condition of keeping the optimal staggered distance value for coal seam Nos. 1 and 2 unchanged. These results could be beneficial in reduction of surface subsidence and may also have specific practical engineering significance.

Field and simulation study of the rational retracement channel position and control strategy in close‐distance coal seams

“…where m 2 is the mining height of 4# coal seam, H 2 is the average burial depth of 4# coal seam, γ is the average density of overburden, C is the cohesion of coal, φ is the internal friction angle of coal, f is the friction coefficient, ξ is the triaxial stress coefficient, which can be calculated by ξ = (1 + sin φ)/(1 − sin φ), λ is coefficient of horizontal pressure. The stress at point M (x, y) in the floor can be expressed as 43 :…”

“…The stress at point M ( x , y ) in the floor can be expressed as 43 : $$$\left\{\begin{array}{c}{\sigma }_{x}=-\displaystyle \tfrac{2}{\pi }{\int }_{ \mbox{-} {l}_{0}}^{{l}_{3}}\displaystyle \tfrac{y{(x-\eta )}^{2}q(\eta )d\eta }{{[{y}^{2}+{(x-\eta )}^{2}]}^{2}},\\ {\sigma }_{y}=-\displaystyle \tfrac{2}{\pi }{\int }_{ \mbox{-} {l}_{0}}^{{l}_{3}}\displaystyle \tfrac{{y}^{3}q(\eta )d\eta }{{[{y}^{2}+{(x-\eta )}^{2}]}^{2}},\\ {\tau }_{xy}=-\displaystyle \tfrac{2}{\pi }{\int }_{ \mbox{-} {l}_{0}}^{{l}_{3}}\displaystyle \tfrac{{y}^{2}(x-\eta )q(\eta )d\eta }{{[{y}^{2}+{(x-\eta )}^{2}]}^{2}}.\end{array}\right.$$$…”

Failure mechanism and divisional differentiated control of surrounding rock in mining roadway under remaining coal pillar in close‐distance coal seam

“…Shen et al 13 put forward the “three index method” of concentration coefficient, lateral pressure coefficient, and stress gradient to comprehensively determine the reasonable layout range of roadway to solve the proper layout position selection of roadway under residual bearing coal pillar in the close‐distance coal seam, which provided a theoretical basis for the layout of the roadway under residual coal pillar in the close‐distance coal seam. Sun et al 14 calculated the staggering distance expression of multiseam mining using the slip‐line field theory. They verified the roof subsidence coefficient corresponding to the optimal staggered distance by numerical and similar simulation methods.…”