特厚煤层垂直分层区段窄煤柱围岩稳定性及控制技术

Stability and control of surrounding rock of narrow coal pillar in vertical stratification of extra-thick coal se

针对特厚煤层垂直分层区段窄煤柱大变形失稳控制难题,采用理论分析、数值模拟及现场试验相结合的方法,对内蒙古老公营子煤矿特厚煤层窄煤柱围岩稳定性及控制技术展开研究。笔者在对窄煤柱内三向应力计算的基础上,基于摩尔−库伦破坏强度得到窄煤柱平面应变的屈服准则,定性分析了窄煤柱破坏特征及损伤程度演化规律,进一步分析了区段窄煤柱失稳机理及其尺寸效应影响规律,最后给出区段窄煤柱围岩控制关键技术,并通过数值模拟及现场试验进行验证。研究成果表明:①窄煤柱中部破坏程度大于两帮,中部自顶端向下煤体破坏程度由严重向轻微发展。随着宽高比增大窄煤柱内破坏程度及严重破坏区域占比逐渐减小,当宽高比大于1∶1,窄煤柱中下部开始出现大范围的轻微破坏区,当宽高比大于5∶3,轻微破坏区占比超过50%。当黏聚力C≥3 MPa,或内摩擦角φ≥20°时,窄煤柱两帮破坏程度转变为轻微。②工作面回采巷道一侧为窄煤柱低强度承载区,在上部高应力作用下,大范围的低应力承载区煤体向巷道位移,造成两帮持续性大变形,进而影响顶板的稳定性。煤柱高度是中、底分层区段窄煤柱稳定的主控因素,窄煤柱宽高比增大,对高强度承载区承载强度影响程度较小,而低强度承载区承载强度增加较明显,合理的窄煤柱宽高比可平衡煤柱内高、低强度承载区比例,并提高承载强度。③分层窄煤柱留设需考虑工作面两侧采空时围岩稳定性,保证煤柱内部高强度承载区范围大于煤柱宽度及高度的一半,并通过联合加强支护措施使煤柱内形成由浅入深的多重联合控制区,共同维护煤柱的自稳能力。

Aiming at the problem of large deformation and instability control of narrow coal pillar in the vertical stratification section of extra-thick coal seam,the stability and control technology of the surrounding rock of narrow coal pillar in extra-thick coal seam are studied by combining theoretical analysis,numerical simulation and field test.Based on the calculation of the triaxial stress in the narrow coal pillar,the yield criterion of the plane strain of the narrow coal pillar is obtained based on the Mohr-Coulomb failure strength,the failure characteristics and the evolution law of the damage degree of the narrow coal pillar are qualitatively analyzed,and the instability mechanism and size effect of the narrow coal pillar are further analyzed.Finally,the key technologies of surrounding rock control of the narrow coal pillar are given.It is verified by numerical simulation and field test.The research results show that①The damage degree of the middle part of the narrow coal pillar is greater than that of the two sides,and the damage degree of the middle part from the top to the bottom develops from serious to slight.With the increase of width-height ratio,the damage degree and the proportion of serious damage area in the narrow coal pillar gradually decrease.When the width-height ratio is greater than 1∶1,a large range of slight damage area begins to appear in the middle and lower part of the narrow coal pillar.When the width-height ratio is greater than 5∶3,the proportion of slight damage area exceeds 50%.When C≥3 MPa,orφ≥20°,the damage degree of the two sides of the narrow coal pillar becomes slight.②The side of the mining roadway in the working face is a low-stress bearing area of the narrow coal pillar.Under the action of high stress in the upper part,the coal body in the large-scale low-stress bearing area moves to the roadway,resulting in a continuous large deformation of the two sides,which in turn affects the stability of the roof.The height of coal pillar is the main controlling factor for the stability of the narrow coal pillar in the middle and bottom layered sections.The increase of width-height ratio of the narrow coal pillar has little influence on the bearing strength of high strength bearing area,while the bearing strength of low strength bearing area increases obviously.Reasonable width-height ratio of the narrow coal pillar can balance the proportion of high and low strength bearing area in coal pillar.③The stability of surrounding rock should be considered in the design of layered narrow coal pillars when both sides of the working face are mined out,so as to ensure that the range of high-strength bear-ing area inside the coal pillar is greater than half of the width and height of the coal pillar.Through the joint strengthening support measures,multiple joint control areas from shallow to deep are formed in the coal pillar to jointly maintain the self-stability of the coal pillar.