Study On Crack Propagation And Evolution Characteristics Of Hard Rock Under Dynamic And Static Loads Of Secondary Blasting

Hard rock is a common obstacle in coal mining,hindering the progress of the working face.Currently,deep hole blasting is employed to reduce the fracturing of hard rock.However,the efficiency of drilling is low and the range of cracking is limited.Therefore,the development of new blasting technology is a crucial aspect of blasting engineering.This thesis proposes a secondary repeated blasting technology in a single hole for liquid explosives,which can expand the range of blasting cracks and reduce the workload of intensive drilling.The technology allows for the re-expansion of initial blasting cracks.The study systematically investigates the mechanism of fracture development under secondary blasting of hard rock and presents the following main research results.(1)This thesis introduces a rapid excavation project for large section hard rock roadway.The main parameters of deep hole blasting are determined through theoretical analysis and numerical calculation.Field practice of deep hole blasting is carried out and the effect is analyzed.The thesis also summarizes and analyzes existing problems with primary blasting,and proposes a new technology for secondary repeated blasting in a single hole.(2)The law of stress wave propagation and surrounding rock damage evolution under the condition of secondary blasting of traditional grain and liquid explosive charge is studied.The results show that when the liquid explosive is used for secondary blasting,the energy accumulation effect appears along the direction of the initial blasting crack,and the crack propagation effect is good.By analyzing the secondary blasting of columnar charge,it is found that the secondary blasting mainly affects the crack development in the fracture zone.The crack quantification results show that the secondary blasting is 38.5 % higher than the primary blasting.(3)The effects of confining pressure and joint conditions on the development characteristics of blasting cracks were studied.The results show that the cracks preferentially expand along the direction of the maximum principal stress,and the cracks in the direction of the lowest principal stress are inhibited.The secondary blasting can weaken this inhibition and make the cracks in the direction of the minimum principal stress develop.The area between the blast hole and the joint forms a dense ’ triangular ’ damage zone,and the secondary blasting has little effect on the crack development of the jointed rock mass.In addition,the parameter design of secondary blasting hole spacing is studied,and it is found that it is reasonable to set the hole spacing to 1.8 m under the action of secondary blasting.This thesis has 69 figures,8 tables and 73 references.