An investigation into coal damage during blasting.

[摘要] This thesis has investigated ways of exerting control over coal breaking duringblasting. Its ultimate objective has been to optimise the use of explosive energy inblasting so as to ensure reduced production of coal fines in the comminutionprocess.The investigations reported were conducted on laboratory models at a scale of acontrollable energy to enable the development of a theoretical background for thethesis, However, the bulk of the work was undertaken insitu in surface andunderground coal operations. The research was conducted in three phases. Thefirst phase dealt with the approach to modelling the primary crushing mechanismwhich generates the coal fines during the blasting operation. A laboratoryapparatus to simulate blast-generated dynamic loading was devised. Dynamic coalcrushing test conducted on a set of over 150 samples of coal showed anexponential relationship; between the comminution energy and the subsequent coaldamage. A comminution index (Com ) characterising the ability of coal to generatefines was derived.The second phase of the research concerned the field investigations. This had thefollowing double aim: validating the hypothesis of the influence of the dynamicloading of the shock waves and that of the inherent discontinuities imbedded incoal on fines generation; and quantifying the problem of fines in the blastingtechniques currently used in the local mining industry. Three sites were used,namely Kleinkopje of AMCOAL, Greenside of Goldfields and ATC, Tavistock ofJCI.The investigations undertaken at Kleinkopje (surface mining operation) involved thedetermination of discontinuities by logging inherent fractures appearing on 75diamond drilled cores of coal and the monitoring of 76 blasts conducted on thesites sampled for discontinuities. These investigations indicated a good correlationbetween the fines observed in blasted piles and the fracture frequency of the preexisting fractures per metre of coal.The work undertaken in underground collieries (Greenside and Tavistock)demonstrated the enormity of the fines' problem in the local mining operations.Approximately a third of the coal broken underground was observed, in 30 blastssampled and analysed, to fall into the category of fragments of under 6 mm termed'coal fines', Which generate low income.The third phase of the research dealt with the optimisation of coal breaking duringblasting. A series of 100 trial blasts was undertaken with the aim of searching for ablasting technique that enables the generation of fewer coal fines. A number ofoptions were investigated. Trial blasts carried out were evaluated and their resultsare discussed in this thesis.The results of the fieldwork undertaken confirmed that fines generation is sitespeolflc, However, the decoupling technique used with high VOD explosiveproducts may be successfully employed to reduced coal fines generation in strongcoals (few inherent fractures).

[发布机构] University of the Witwatersrand