Determination of roof cutting hole spacing and line position under the action of roof stress
In order to reasonably determine the parameters of hole spacing and cutting line position in roof cutting operation,theoretical analysis was conducted to explore the calculation basis of hole spacing under the comprehensive action of roof stress and guide the selection of roof cutting line position.The following beneficial findings were obtained.The range of cracking induced by deep-hole blasting is limit-ed,and the theoretical spacing between blast holes is 10-15 times the diameter of the blast holes.In blasting practice,a smaller hole spacing conduces to achieving a better planar cutting effect.However,considering the comprehensive action of roof stress,obvious directional cracks are also observed when the spacing is 100 times the diameter of the blast holes.Deep-hole blasting promotes the severity of roof damage.Furthermore,the principle of the comprehensive action of roof stress is revealed by defining the coefficient of the cutting line position,and a larger value of the coefficient corresponds to more flexible selection of cutting line position and wider cutting timing.In roof cutting operation,the roof cutting po-sition is ahead of the end of the suspension beam by at least 60％of the weighting step distance in the case of Φ90 mm holes with a spacing of 2 m.When the hole spacing ranges from 8 m to 10 m,the roof cutting position approaches the fixed end of the suspension beam,being rather constrained.At this time,the roof stress will play the major role in roof cutting.
roof stressroof cutting and pressure reliefhole spacinghard roofdeep-hole blasting
万方数据
维普
