Failure characteristics of extra-thick coal seam under goaf based on double yield model

Abstract

This paper aims to study the influence of the goaf in the upper coal seam on the overlying ultra-thick coal seam and determine the dislocation distance in the roadway layout of the lower coal seam. Based on finite difference method, this research, takig Tashan Coal Mine as the engineering background, established Mohr-Coulomb and double yield constitutive models to invert the rock strata and the rock mass in the caving zone. The failure law of the ultra-thick coal seam under the influence of the overlying close goaf was studied on the basis of goaf and the residual coal pillar. In addition, the distribution law of stress field and the failure range in the coal seam under the goaf were clarified. With the theoretical analysis and the field borehole peep results, the reliability of the numerical method in this paper was verified, and the inner interlocked distance in the roadway layout of the lower coal seam was determined. The results show that the residual coal pillar has the greatest influence on the mining of the lower coal seam. The stress field under the residual coal pillar forms an approximate “normal trapezoid” influence range in the lower coal seam, with the width of the upper and lower being 32 m and 56 m respectively. The plastic zone under the residual coal pillar is distributed in an “inverted trapezoid” in the lower coal seam, and the width of the upper and lower is 81.36 m and 61.47 m, respectively. The inner interlocked distance of the roadways of the lower seam should be 13.5 m.

Keywords

• close goaf
• double yield model
• residual coal pillar
• underlying coal seam
• failure characteristics