基于颗粒流的倾斜厚煤层坚硬顶板运动失稳规律及水力弱化参数研究

Study on movement instability law and hydraulic weakening parameters of hard roof in inclined thick coal seam based on particle flow

为了探究倾斜厚煤层坚硬顶板的运动失稳规律,基于PFC^(2D)离散元颗粒流分析软件建立倾斜厚煤层采动覆岩的数值模型,并针对倾斜厚煤层坚硬顶板大面积悬露问题进行水力弱化方案设计,分析不同压裂参数对倾斜厚煤层坚硬顶板水力弱化效果的影响,并提出一种水力弱化参数优选方法。研究表明:倾斜厚煤层的坚硬顶板初次来压以一种“堤坝体”的岩块结构破断,采空区上覆岩层垂向应力表现出非对称特征,在纵向上随工作面推进呈阶梯状垮落;针对倾斜厚煤层大面积悬露提出4种不同压裂角度,3种不同压裂高度的水力弱化方案,结果表明压裂角度为“直角”,压裂高度为基本顶厚度一半的弱化方案可以达到预期弱化效果,坚硬顶板水力弱化影响区域来压强度整体降低,来压峰值压力降低约42%,来压步距降低约52%;综合考虑施工难度和成本,基于弱化程度和压裂角度、高度之间的关系,对倾斜厚煤层坚硬顶板水力弱化参数进行优化,提出一种倾斜厚煤层坚硬顶板非充分定向水力弱化参数的优选方法,于1E201工作面进行工业性试验并取得了良好的顶板弱化效果。

In order to investigate the motion instability of the hard roof in incline thick coal seam,a numerical model for mining covered rock in such seam was established using PFC^(2D)discrete element particle flow analysis software.A hydraulic weakening program was designed to address the issue of large area hanging arch in the hard roof.The study analyzed the influence of different fracturing parameters on the effectiveness of hydraulic weakening and proposed an optimization method for selecting hydraulic weakening.parameters.The study revealed that the hard roof of incline thick coal seam undergoes a“Dam-shaped block”breakdown under initial weighting,and the vertical stress of overlying strata above the goaf exhibits asymmetric characteristics,resulting in stepped collapse in longitudinal direction as the working face advances;Four hydraulic weakening schemes with different fracturing angles and three different fracturing heights were proposed for large area hanging arch of incline thick coal seam.The results showed that the weakening scheme with a fracturing angle of“right angle”and a fracturing height of half of the thickness of the basic roof achieved the expected weakening effect.The weakening scheme reduced the hydraulic weakening influence area of the hard roof,resulting in an overall decrease in ground pressure strength,with a reduction of about 42%in peak pressure and 52%in weighting step distance;Considering the construction difficulty and cost,the hydraulic weakening parameters of the hard roof of incline thick coal seam was optimized.Based on the relationship between weakened degree and fracturing angle and height,a preferred method of nonfully oriented hydraulic weakening parameters of the hard roof of incline thick coal seam was proposed.An industrial test was conducted in the 1E201 working face,yielding a significant weakening effect on the roof.