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1、Non-explosive Rock Breaking Technologies for Safe and Continuous MiningK.K.KabongoKey words：Mining Consultant，Yonke Services (Pty) Limited，31 Impala Road Chislehurston，Sandton，Johannesburg，RSAABSTRACT：Several mines in South Africa (SA),like in many other parts of the world, use drill and blast as me
2、ans of rock breaking for ore extraction. Despite cost effectiveness high explosive mining does not guarantee optimal total mining costs.Its low energy efficiencies and the hazardous nature of blasting, i.e. poor safety records especially in deep mines, create a need for intensive reseach and develop
3、ment into safer and more productive technologies. Surely mechanised mining is the ultimate option. Many attempts to use heavy machines in narrow vein deposits at great depths have however resulted in disappointment. Over the last three years, the quest for nonexplosives breaking technologies has gai
4、ned momentum. The industry is desperately looking for a face saving system to uplife productivity , ensure safe mining underground, prevent and damaged-control the impact of the devastating HIV/AIDS on the future of mining. Propellant based non-explosive rock breaking is positioning itself so as to
5、capture the opinion in the industry. It is considered a midway between cheaper but life-threatening explosives and the capital intensive and uncompromising mechanised mining.Many non-explosive products being trailed in the industry: Swartklips Boulder , Rocksplitter, Brandrills Penetration Cone Frac
6、ture (PCF),NXCOs Nonex and Altexs Safex to name a few . All these systems have unique merits and they all claim different levels of success in breaking rock under varying conditions, however they all lack the Herculean power (Cunningham 2002), “the oomph”,to properly clean out the rock burdens consi
7、stently to the satisfaction of the industry . Fundamentally these systems appear to lack in containing the blast gas energies in the rock to mature burden fracturing. Rockdusters and Conmin 101 are the newest products to make an appearance . They claim to have addressed this shortcoming with contept
8、. They still have to prove in practicaltrials what appears like an obvious edge over precursors, that capacity of holding gases in blastholes for long duration. Ever though the industry expectation of continuous mining operationts is still a dram , as non-explosive mining technologies developed to d
9、ate , have not succeeded to demonstrate such capabilities . This paper intends to discuss the advantages of non-explosive rock breaking systems and to present some results of trial blasts to highlight the way forward towards achieving continuous mining , improved health and safety and higher product
10、ivity that impacts on the industry bottom lines.1INTRODUCTIONDrill and blast technology has indisputable merits of breaking the rock. However it is always associated with major health and safety concerns owing to direct aftermath side effects such noise, fly rocks, toxic fumes, dust, high concussion
11、, accidental detonations and management of misfires. Indeed, the SA industry has managed to scale down and manage these hazards relatively well, given the risks involved and the statistics of accidents recorded to date. However since human life should be rightly valued, the national expectance is ze
12、ro accidents at any cost. Thus the reason for this quest by all concerned parties is to work towards a safer mining system that ensures sustainable mining to well take the industry into the future. Cunningham (2002) highlights the major shortcoming of conventional high explosive mining. He observes
13、that underground ore production is limited by disruption of operations imposed by mining legislation associated with blasting. Full shift continuous operations are impossible owing to the withdrawal time required. Workers vacate the workings shortly before and during blasting. There is a working pre
14、scribed re-entry period that ought to be observed while blast fumes, noxious gas and dust settle. Non-explosive rock breaking systems claim the advantage of no concern with such huge loss of working time. Several systems have been developed and put forward to the industry. Despite their subtle diffe
15、rences warranting their individual patents, they all have in common the following claimed features: Non-explosive low concussion rock breaking Less fines and dust generation Improved hanging wall conditions due to low concussion Low toxic fumes, enabling immediate re-entry and continuous mining.2 NO
16、N-EXPLOSIVE ROCK BREAKINGSA mining industry has one of the highest rate of mining casualties in the world mainly due to the great depth of mining (2 to 3 kilometres under the ground, ever more ). The unique geotechnical rock conditions are generally characterized by heavily fractured rock in stops a
17、nd haulages as well as a highly sesmic active ground conditions.High explosive mining does add to the ground conditions described above another safety concern that is born out of the enormous energy generated by blasting,which is often poorly accounted for.Considerable portion of blast energy remain
18、s locked up in hanging walls of mining excavations.Without prior warning such energy comes down often triggering bloody falls of ground that frenquently result in accidents varying in intensity from small cuts to multiple fatalities .Tabulated below are statistics of accidents recorded in SA mines f
19、or a period of nine years from 1990 to 1999.Table 1. Statisics of high explosive related accidents in SA mines.SA mines accident statistics from 90-99Total injuredTotal disabledTotal killedTotal accidentsFall of groundMisfires Exposure to blasting fumesOther explosive related accidents17286124993015
20、472901822997417180Table 1(above)depicts the horrendous reality of SA mining industry that may be summed up in the following:Every single year high explosives in the industry cause death to over one hundred and fifty people,injure over one thousand eight hundred people and inflic permanent disability
21、 to some ten people.This is the scenario that non-explosive rock breaking technologies intend redressing beside the added advantage of increased production rates.Path and underlying principles of non-explosive rock breaking systems Impact miningIn the early nineties, the mining industry witnessed an
22、 eagered search for paradigm shift in mining underpinning intensive reaserch for safer and more productive rock breaking technology for narrow reef mining. The trend was fuelled by the need for substituting the inherent disadvantages of conventional labour intensive method of drilling holes and deto
23、nating violently chemicals into the rock to extract portions of orebodies. In already difficult ergonomical conditions, i.e. deep mine heat load, highly stressed rock and confined spaces, explosions are always perceived to sensibly obscure the positive contribution of the industry. Financial Mail, S
24、eptember 1993 reports that impact mining considered revolutionizing mining since the eighties. Intitial exploratory trials were carried out at Doornfontein mine. Number of mines which followed suite to pioneer the process, i.e. Kloof Mine, claimed an upper hand for the technology as it yielded lower
25、 working costs and high production rations. However the technology was not further developed owing to its lack of flexibility associated with high level of mechanisation. So despite being non-explosive impact mining was seen as part of drive towards mechanized-mining in deep mines, which falls outsi
26、de the scope of this paper.NXCOs Nonex technologyNonex technology is also based on the use of a propellant cartridged in a drilled hole and stemmed by aggregates (stemming column) to fill the blasthole. This system claims to have substantially improved the geometry and nature of the stemming materia
27、l used to confine the propellant in the hole therefore resulting in a much better in-hole confinement of gas energies. In addition Nonex cartridges are 100 non-explosive and totally inert. Ignition is obtained by low voltage electric power a part from which any other means would completely fail to s
28、et off the cartridge, hence its extreme safety in handling and transportation.The Nonex cartridge system works on the principle of a balloon to seal off the hole and avoid premature gas escape during the pressure build-up. This is a considerable advantage as escaping gas compresses air at the interf
29、ace cartridge/rock/stemming, interfering thus with the pressure build up in the hole. Indeed, the gas fills the annular space around the cartridge as well as filling all the new openings generated by induced and/or in situ fractures, thus lowering the pressure in the blasthole. In a non-expanding ca
30、rtridge, the pressure is further lowered by the movement of the stemming in response to the slow pressure build-up in the hole. In principle, the build-up of pressure should be fast enough so that inertia prevent appreciable stemming movement during the critical period of gas advance into the rock f
31、racture network. The slow pressure build-up, on the other hand, results in an early release of gas from the hole before the rock fracturing process is completed. Work by Ozbay (1982), and other earlier works, ascertained that the fracturing process in hard rock requires some 3 to 10 microseconds to
32、complete. The Nonex cartridge is provided with a pressure release valve that is activated on ignition, inflating the cartridge to seal off the hole and keeping the pressure within the hole for as much time as the rock needs to crack before the release. The system greatly reduces the probability of c
33、artridge malfunctioning in the blasthole. An additional advantage is that ever in the case of malfunction,a Nonex charged blasthole could be drilled into by the rockdrill without danger of detonation. There is no potential danger as the cartridge and the igniter are both non-explosives. One cannot t
34、alk of misfire in this case; rather a malfunctioning that can easily be remedied.ALTEXs SAFEX technology Originally from Scotland this technology is claimed to be suitable for both secondary and primary rock breaking in surface as well as underground mining. It is a relatively new product in the ind
35、ustry and so it has not attracted much interests. It is based on the use of drilled hole in which a special propellant cartridge is charged in a bottom-priming configuration. The blasthole is stemmed with sand and a double chemical concoction, which mixt with the sand to from a sort of paste in the
36、hole. The paste expands to fill up the section area of the hole and dries quickly into a plug that seals tightly the hole. The propellant charge is initiated by an AEL made electrical/combustion igniter named “sure start”. It is basically an electrical fusehead that is made to set off normal igniter
37、 cord for combustion initiation. Safex field trials conducted at a chrome mine as well as at a platinum mine respectively in the Eastern and Western Bushveld did not yield conclusive evidence to warrant recommendation of the system for routine mining. As in any R&D, the product is being improved (ba
38、ck to the drawing board) for further attempts.Salient features of non-explosive rock breaking The learning curve of non-explosive rock breaking technologies has been steep since they are meant to compete with settled high explosives that have built the mining industry wealth and reputation over many
39、 years.It is against this background and the general conservatism that riddles the industry that the new comers have to battle .Whatever the standoff will be, it is worth highlighting the following salient features of these new technologies.Motivational edgeFull day work in stops with shift relief u
40、nderground can be achived.Thus continuous mining and its several advantages discussed below ceases to be a dream of the industry but a reality applicable for both primary and secondary, surface and underground mining.Legal advantageNon-explosive mining offers tremendous advantages in that countless
41、legal implications would fall through and would no longer haunt the industry. By virtue of using safe-to-handle energetic materials, i.e. propellant instead of explosives, the perception of mining being the peacetimes most killing industry would fade away.Technical argumentNon-explosive rock breakin
42、g technologies are being introduced at the time when the mining industry is very environmental conscientious. Energetic products are designed with health and safety concerns in mind. Components are user-friendly and life entertaining therefore no special dispositions should be required in their hand
43、ling and transported as pre-assembled units ready for charging in the hole or can be assembled on site shortly before use.The system guarantees cost-effective mining, which may come in as an oxygen line to deep and marginal mines threatened with closure. This would boost the industry and contribute
44、to ensuring its global competitiveness.The technology is set to revolutionise rock breaking in mining. Short of replacing high explosives this technology would compete favourably and capture a sensible portion of the commercial explosives market. Its edge over explosives mining is embedded in the ge
45、ntleness of the propellant combustion reaction. The slow release of equally huge energy like that from explosives enable more useful work to be done in the rock, i.e. the longer the gas containment in drilled holes the better the breaking and the lesser the fine generation (crushing).Economic benefi
46、ts Non-explosive rock breaking is expected to offer the following advantage:Safety aspects: Little or no harmful nitrous fumes are created, Little or no dust created when the blast takes place, Little or no fatal injury from accidental detonation, Due to lower concussion, fewer fractures in the soli
47、d rock surrounding the blasted area, which implies less rockfalls. (Great reduction in hanging wall fracturing). Temporary supports are not blasted out leading to lower support costs. Number constraints and current regulations applicable to dangerous commercial explosives areavoided. Working time re
48、straints in stopes are greatly reduced. Few misfires. Ever if they occur one can safely drill through them as the propellant would be rendered harmless on contact with the water.Productivity aspects: Production process to be continuous, i.e. no need for lengthy re-entry periods that underpins curren
49、t inefficient work schedule of one blast per day. High monthly calls. A double advance per day in a panel is achievable. A slight increase in overheads (labor force and drilled meters ) that would be compensated by the extra advance production. Possibility of multiple breakings(3 to 4 times in 24 hours, provided that cleaning technology follows suite). Optimum utilization of the labor force. C
