Analysis on Para-Static Stress Field Features of Pre-Cracking Blasting in Seam

In order to analyze the distribution law of the para-static stress field in the seam after the pre-cracking blasting, based on the elasticity mechanics super position theory, the borehole stress concentration and thick wall barrel principle, the paper had an analysis on the radial stress, tangential stress and shear stress distri bution features of the surrounding coal mass along the blasting chamber. The results showed that the radial stress and shear stress in the blasting chamber wall would b e a fixed value, the tangential stress would be related to the location and the crack expansion would be firstly opened along the horizontal direction.In the seam, the tan gential in an azimuth angle θ=0 direction would be always in a tension stress and a min value would be at the distance of r=10a (a is the radius of the blasting chamber) to the blasting chamber center.At the θ=π/4 and θ=π/2 direction, the variation tendency of the shear stress would be same and the pressure stress would steadily beco me the tension stress.The shear stress would only occur at the θ=π/4 direction.On the blasting chamber wall, the shear stress value would be 0.At r=3a, the shear stres s would reach the max value-4σ2/3 (σ2 is the horizontal stress of the surrounding rock) and then the shear stress would be steadily reduced.At a infinite remote locatio n, the shear stress would become a horizontal stress of the surrounding rock.The stress distribution features in the seam after the pre-crack blasting could provide the t heoretical reference basis to the optimized design of the seam gas drainage.