Study on movement instability law and hydraulic weakening parameters of hard roof in inclined thick coal seam based on particle flow
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 PFC2D 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 non-fully 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.
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