浅埋近距煤层开采三场演化规律与合理煤柱错距研究

为探索浅埋近距煤层开采基于三场(应力场、位移场和裂隙场)演化规律的合理煤柱错距,实现井下减压与地表减损开采,以陕北柠条塔煤矿北翼东区1^-2与2^-2煤层开采为背景,采用FLAC^3D,UDEC数值计算、物理模拟及理论分析相结合的方法,揭示了近距煤层开采覆岩与地表应力场、位移场和裂隙场演化规律,掌握了不同区段煤柱错距对煤柱集中应力、覆岩与地表位移及裂隙演化的影响,提出了基于三场演化规律的区段煤柱错距确定方法。研究表明,近距煤层开采的裂缝集中发育和地层拉、压应力集中源于煤柱引起的非均匀沉降,上部单一煤层开采后,在底板形成煤柱高应力区、低应力区和采空区中部高应力区,为避开上、下煤柱垂直应力叠加,下煤层巷道应布置在低应力区范围内。近距煤层开采的地表拉应力场和位移场与煤柱错距存在密切联系,通过合理的煤柱错距布置,可以减缓地表下沉的"波状"幅度,减轻地表拉应力和水平变形。随两煤层煤柱错距增大,覆岩裂隙场由叠合逐渐分散,对应地裂缝逐渐减小,煤柱错距对其上部的覆岩裂隙与地裂缝起控制作用。建立了应力场-位移场-裂缝场耦合控制模型,提出了煤柱错距的计算方法,可实现减轻地应力集中和地裂缝发育的耦合控制。本研究得到实测验证,并在柠条塔煤矿后续开采布置中应用。

Research on three-field evolution and rational coal pillar staggered distance in shallow buried closely spaced multi-seam mining

In order to explore the rational staggered distance of coal pillars based on the three-field (stress field,displacement field and fracture field) evolution and realize the reduction of ground pressure and surface damage in shallow buried closely spaced multi-seam,the mining at No.1-2 and No.2-2 coal seams in the east of northern Ningtiaota coal mine was investigated in this study.Combining with FLAC3D,UDEC numerical calculation,physical simulation and theoretical analysis,the three-field evolution of overlying strata and ground surface in closely spaced multi-seam mining were revealed.Meanwhile,the relationship between the coal pillar staggered distance and the concentrated stress,displacement and fracture evolution of overlying strata and surface was obtained,the rational coal pillar staggered distance based on the three-field was put forward.The results show that the concentrated development of fractures and the concentrated tensile and compressive stress are due to the uneven strata subsidence by coal pillars.After upper single seam mining,high stress area of coal pillar,low stress area and high stress area in the middle of longwall face were formed in the floor.In order to avoid the vertical stress superposition of upper and lower coal pillars,the lower roadway should be placed in the low stress area.There was a close relationship between tensile stress field,displacement field of surface and coal pillar staggered distance.Through rational arrangement of coal pillars,the “wavy” amplitude of surface subsidence decreased,and the tensile stress and horizontal deformation were effectively controlled.As the coal pillar staggered distance increased,the fracture field changed from superposition to separation,and the surface fractures decreased gradually,consequently,the coal pillar staggered distance had control function on overlying strata fractures and surface fractures.Finally,the coupling control model of stress field-displacement field-fracture field was established,and the calculation method of coal pillar staggered distance was proposed.It can realize the coupling control for reducing the concentration of ground stress and development of ground fractures.It is verified by engineering practice,and will be adopted in the subsequent layout of Ningtiaota coal mine.