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An energy-gathered roof cutting technique in no-pillar mining and its impact on stress variation in surrounding rocks |
HE Manchao1,GAO Yubing1,2,YANG Jun1,2,GUO Zhibiao1,2,WANG Eryu1,2,WANG Yajun1,2 |
(1. State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China;2. School of Mechanics and Civil Engineering,China University of Mining and Technology(Beijing),Beijing 100083,China) |
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Abstract Based upon the cutting cantilever beam theory and the construction experience in Ningtiaota coal mine,the mechanism of gob-side entry by roof cutting was analyzed and the key processes of this novel no-pillar mining method was proposed. A double blast-hole mechanical model was established to obtain the cutting-through criterion of adjacent holes. The key parameters for the cumulative blasting was obtained considering the roof lithology of mining face S1201. The stress distribution and development before and after the roof cutting in both the mining face and the entry were studied systematically by means of theoretical analysis,numerical simulation and field measurement. The results indicate that the mine pressure at the working face and retained entry changes a lot before and after the roof cutting,mainly because the cutting process alters the roof connection and prevents the stress propagation from the gob roof to the entry roof. The periodic pressure strength reduces while the periodic roof weighting pace increases to a certain extent within the area of roof cutting influence. Analysis also shows that the supporting role of the gangue filling body is the immediate reason for the pressure strength reduction,and the decrease of the effective loading acting on the key stratum is the substantial cause for the roof weighting pace to increase. The gob rock masses experience the caving,compacting and stabilizing processes due to the roof cutting. Fully utilization of the bearing capacity of hulking gangues and the collaborative support of surrounding rocks are the effective ways to reduce the supporting intensity and increase the stability of surrounding rocks.
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