Statistical analysis of distribution patterns of coal seams in fold zones in Northwest China

摘要

The mechanisms for rock bursts occurrences in fold zones are complex,and the redistribution of in-situ stresses is closely related to the complexity of the structures.Analysis of the geomorphology of fold structures and changes of coal thickness can help identify zones prone to rock bursts to improve safety and productivity in coal mines.This study investigated the distribution characteristics of fold structures in coal seams in fold zones in four mines in northwest China.Geometrical characteristics of fold structures in coal seams and changes of coal thickness were analysed,based on comprehensive evaluation indexes,such as the length–width ratio of folds,interlimb angle,ratio P1 of projected width of fold limbs to that of the hinge zone,curvature ratio P2,the maximum curvature and amplitude.The statistical analysis of the four coal mines shows that the length–width ratio of folds changed from 0.78 to 2.03 and the maximum curvature of cross sections of folds was less than 0.04.The curvature ratio of cross section of a fold in the structure was no more than 1.4 and the interlimb angles of cross sections of 89%of folds were larger than 150.Gentle fold structures were dominant and the specific geological morphologies were domes or basins.The isopleth of coal thickness above the coal mines showed a fluctuation trend similar to the contour line of the floor of coal seams.The coal thickness in an anticline area was smaller than that in the neighboring syncline area.Therefore,the overall variation of coal thickness in the mining areas was likely to have a relation with the direction of the regional principal stress.