Study on evolution characteristics of uneven stress field in mining-induced fold tectonic area

As one of the geological structures formed by crustal movement，the non-homogeneous stress distribution of nearby strata during the fold area is the main factor inducing coal burst.Based on the engineering geological background of No.21221 mining face of Qianqiu Coal Mine in Yima Mining Area，the numerical model is established by applying non-homogeneous structural stress to analyze the evolution characteristics of the stress field in the fold area during the coal seam mining，and strata behavior regularity in different areas of fold structure is also studied.The results show that the distribution of in-situ stress field in the fold area has obvious regional spatial distribution.It means that vertical stress and horizontal stress show different zoning characteristics in fold syncline and anticline axis，and stress concentration occurs at the syncline axis.As the working face advances through the syncline and anticline，the horizontal stress and the vertical stress form the oval pressure relief area in the roof and floor.The evolution of vertical stress relief zone is gradually expanding along the normal direction of fold syncline or anticline，and the vertical stress concentration area appears in front of the working face，and it extends away from the axis.The horizontal stress concentration area appears in the vertical direction of the working face，and it gradually develops to the far distance of the roof and floor，and the release degree of horizontal stress in the roof is higher than that in the floor during the relief area.As the working face advances through the syncline and anticline，the peak value of abutment pressure increases with the increase of mining distance，and the stress concentration coefficient increases at first and then decreases.Compared with the process when the mining face is mining from the syncline axis，the abutment pressure is larger when the mining face is mining from the anticline axis.When the mining face advances to the fold axis，the stress concentration degree of immediate roof compression state decreases gradually，and the process of reduction is accompanied by the phenomenon of sudden increase in energy release，which is extremely prone to induce the coal burst.