| Rock-burst is one of the most typical rock or coal dynamical disasters in coal mine. Especially the rock-burst dynamic disaster which is island coal pillar in extremely thick coal seam combined with hard and thick roof is more outstanding and complicated and destructive, and the relative study is less. Therefore, this paper try to explore the mechanism and staggering floor layout prevention technology of rock-burst which occurres in island coal pillar with hard and thick roof in extremely thick coal seam by some methods including theoretical analysis and numerical simulation and field practice.Theoretical analysis shows that stress concentration degree and bending deformation energy accumulation rate in the roof gradually increase with mining neighbor conditions gradually deteriorated from the four sides all entity to four sides all mined,. Especially those island coal pillar with hard and thick roof are easier to form long arm "T" shaped overlying strata structure which have a large area of overhang roof that can cause a large range and severity of strata movement. Thus,dynamic load generated from roof rupture and formation are readily applied to coal pillar in the form of stress wave at ambient extractive disturbance. However, island pillar area is already in a high state of stress by the clamping action of a large area of overhang roof,when its original high static superimposed with the dynamic load exceeds the ultimate strength of coal and rock, which resulting in coal and rock that are already in limit state instability failure, can cause a massive dynamic disaster impact. That is, the mechanism of rock-burst is induced by the superimpose of static load which is the leading factor and dynamic load which is the inducing factor.Calculation results of stress field of floor coal in island coal pillar show that coal stress difference decreases with depth increasing in the floor of island pillar, however, stress concentration degree and stress difference vary significantly with stress concentration factors changing. reduced stress and reduced stress changing area are both exist in Floor, which may be expressed as the outer envelope area of 0.1q stress and 1% stress change rate contour. However,non-uniform stress is the leading reason causing roadway support structure damage and deformation, therefore staggering floor layout roadway should be arranged within the superimposed area of reduced stress area and reduced stress change area.0.1q and 1% contours are respectively defined the boundary of reduced stress and reduced stress change area, with the angles between the vertical line is defined as the reduced stress anglekq and reduced stress change angle sq.Stress concentration factor are positive linear correlation between the two factors, while k <11, k sq <q, thus, comprehensive stress angle should be represented by the reduced stress change angle., and the reasonable distance is 1 2 0l =(h +h) tan f-x. And using1210 island coal pillar whose two lane has taken staggering floor layout as an field example to verify the reasonableness of the calculated distance.Calculations results from numerical simulation FLAC3 D show that the stress concentration factor of 1210 and downhill island coal pillar are 3.8 and 2.8, verifying that the island pillars are of high stress concentration degree,and the risk of rock burst are strong. analysis and comparison of the stress and deformation of various programs show that the staggering floor layout program for exclusive return-air gateway is in the reduced stress area because of its above mined-out area,and its rock stress and deformation is much smaller than all the other programs, which is very favorable for the prevention of rock-burst.Using barapukuria coal mine 1108 island coal pillar as a background to analysis the rockburst mechanism of island coal pillar with hard and thick roof, and combined with the field example of 1210 islands pillar whose two lane has taken staggering floor layout, results verifying that the staggering floor layout technology is reasonable and excellent to prevent rock burst... |
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