煤层预裂爆破准静态应力场特性分析

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

为了分析预裂爆破后煤体内准静态应力场的分布规律,基于弹性力学叠加理论、圆孔应力集中和厚壁筒原理,对爆腔周围煤体的径向应力、切向应力和剪应力分布特性进行分析。结果表明:在爆腔壁上,径向应力和剪应力为定值,切向应力与位置有关,裂隙扩展首先沿水平方向开始;在煤体内,切向应力在方位角θ=0方向上始终为拉应力,在距爆腔中心的距离r=槡10a(a为爆腔半径)存在最小值;在θ=π/4和θ=π/2方向上,切向应力变化趋势相同,均由压应力逐渐变为拉应力;剪应力只发生在θ=π/4方向上,在爆腔孔壁处,其值为0;在r=槡3a处,剪应力达到最大值-4σ2/3(σ2为围岩水平应力),随后逐步趋于减小;在无穷远处,剪应力变为围岩的水平应力。预裂爆破后煤体内的应力分布特性,可为优化煤层瓦斯抽放设计提供理论参考依据。

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 superposition theory,the borehole stress concentration and thick wall barrel principle,the paper had an analysis on the radial stress,tangential stress and shear stress distribution 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 be 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 tangential 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 become 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 stress 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 location,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 theoretical reference basis to the optimized design of the seam gas drainage.