Active Relieving Control Of Hard Roof Over Gob-side Entry Retaining In1100m Deep Mine

This paper used the method that combine theoretical analysis, numericalsimulation and industrial test, studied the broking form of main roof over gob-sideentry retaining and its effect to structural stability. Analyzed structual form andstability of hard roof after pre-splitting blasting, Simulated the effect of pre-splittingblasting relieving, Proposed the Pre-splitting Blasting scheme of hard roof andsurrounding rock controlling scheme. The industrial tests have successed and resultsare as followed.(1) Proposed four possible breaking positions of main roof over gob-side entryretaining, identified the maximum bending moment of main roof in differentlocations by theoretical calculations. Believed that in non-hard roof circumstances,the breaking of main roof occurs at the top of the outer wall or over entity coal. Thebreaking position of hard roof only occurs at the top of entity coal.(2) Theoretical calculated and contrastively analyzed the influence law ofdifferent factors to small structural deformation in the conditon of hard roof andnon-hard roof. Closer breakage location of main roof to coal wall is, longer thelength of the key block is, smaller the deformation of coal-wall and filled-wall willbe. On the contrary, greater will be. The deformation of filled-wall and coal-wallunder hard roof is4and2.5times greater than that under non-hard roof, so manualintervention measures should be taken.(3) Proposed two kinds of structure forms and three kinds of stress model ofmain roof after pre-splitting blasting, calculated the support resistance of fillingbody under different loading conditions. The two kinds of structure forms includearticulation and cut off. There is a pressure that the broken block to lateralboundaries when they hinged out of filled wall, and there is no mechanical contactwhen they cut off out of filled wall. The collapse block will surpport the main roofin situ when main roof occurs secondary breaking, and will protect the filled wall.(4) By analyzing the geometrical and equilibrium conditions of hinge structure,believe we shound try to increase the radius of blasting weakened region, in order toachieve the purpose of the breaking roof is not in contact with the roof in situ.Analysed the requirement that the roof can form a stable structure after the hard roofoccurs secondary breaking, it is not conducive to small structure stability of gob-sideentry retaining when blasting weakness area radius is too large. Therefore, the blasting weakness area radius R exists a reasonable range of valuesL2m22hm/2L/2R222L max (h m)/(2L max) L/2.(4) Analysised the characteristics of roof collapse, surrounding rockdeformation and stress distribution in three conditions include not cutting+caving,single cutting+caving and double cutting+caving by UDEC simulation. The resultsshow,①Three cases, main roof is respectively breaking above the entity coal andforming situ articulated structure, outer the filling wall and forming dislocatedarticulated structure, outer the filling wall and directly cut off.②Pre-split blastingadjusted the breaking position and morphology of hard roof, reduced the amount ofdeformation of gob-side entry retaining, more fully relief the reducing degree ofdeformation will be greater.③Pre-split blasting optimized surroundung rock stressfield, lateral support pressure peak decreased after the bursting, peak stress pointtransfer to shallow rock.(5) In the end of the paper, combined the conditions of Pingdingshan No.12Mine, proposed the Pre-splitting Blasting scheme of hard roof and surrounding rockcontrolling scheme, and shown a engineering practice.