Mechanisms And Application Of Energy Vibrational Release And Structural Regulation Induced By Roof Deep-hole Blasting For Preventing Coal Bursts

Coal bursts in coal mines are largely driven by the near-field thick hard roof layers over coal seams.A common technique for mitigating coal bursts caused by near-field thick hard roof layers is roof deep-hole blasting.For its promotion and application,in-depth research of the mechanism of roof deep-hole blasting for preventing coal bursts is of considerable theoretical and practical importance.Therefore,using a combination of theoretical analysis,physical and mechanical experiments,similarity experiments,numerical simulations,and engineering practices,this thesis presented a systematic study on the mechanisms and application of energy vibrational release and structural regulation induced by roof deep-hole blasting for preventing coal bursts in coal mines.Roof deep-hole blasting caused strength weakening and energy vibrational release of rock.For column charge blasting in rock with load-bearing and energy storage,a superposition model for the propagation of blasting stress waves and rock damage criterion was developed,and the impacts of blasting on rock structure failure and strength weakening were presented.The dynamic evolution of stress and stored elastic energy in rock during blasting was obtained using a mechanical model for the transient unloading of stress during blasting.Then it was suggested that blasting in rock with load-bearing and energy storage would have an energy vibrational release effect.Rock with load-bearing and energy storage under impact loading was studied for its dynamic damage characteristics and energy dissipation using the SHPB equipment,which can apply axial and confining pressure.The effects of blasting on rock’s strength weakening and energy vibrational release were verified.Finally,the impact of factors including impact pressure,axial and confining pressure,and impact cycle numbers were investigated.This thesis proposed the mechanisms of stress reduction and seismic mitigation of roof deep-hole blasting for preventing coal bursts through coal-rock structure regulation during the mining of working face.Roof deep-hole blasting can directly reduce the static stress distribution and energy accumulation in coal rock mass,and regulate the roof-coal-floor system structure at the working face and the overburden structure in the gob.Firstly,the existence of the blasting damage zone can effectively block the stress transfer path in the roof-coal-floor system structure and weaken its strength and deformation parameters.Further,it can promote the system structure from brittle to ductile failure,and reduce its energy accumulation and release capacity.Secondly,roof deep-hole blasting can cut off the continuity of roof stratas in the horizontal direction,then the roof strata could break and collapse at the pre-splitting position.As a result,the breaking step distance of the overburden was reduced,and the structure form of overhanging roof behind coal wall changes from long"arc-shaped triangle"to short"trapezoid",which reduces the loading capacity of overhanging roof on coal seam and the dynamic stress produced by its breaking.Finally,the effects of blasting intensity,location,medium properties,stress environment and fan-hole initiation patterns on the blasting damage and vibration were investigated.Based on blasting-induced microseismic data,a technique for assessing the efficacy of roof deep-hole blasting was developed.The correlation between the characteristics of blasting-induced microseismic and the energy release effect was analysed,and the blasting effectiveness index B_e is constructed and the key parameters are determined.The rationality of the index was verified by using data from 181 rounds roof deep-hole blasting in three coal mines,and the classification standard for the evaluation of effectiveness was developed.Several widely used techniques for assessing blasting performance were also covered,along with discussions of their applicability and instances of successful application.Based on the mechanism of energy vibrational release and structural regulation induced by roof deep-hole blasting for preventing coal bursts,the engineering practice of roof deep-hole blasting was carried out in the 1210D isolated coal pillar of Mengba coal mine and W1103 working face of Yutian coal mine,Xinjiang.The proposed mechanism of roof deep-hole blasting for preventing coal bursts and its effectiveness evaluation method were verified.The safe and efficient production of the mine was guaranteed.Good social and economic benefits have been achieved.This dissertation contains 151 figures,19 tables and 216 references.