Search Documents

By P D. Katsabanis

The phenomenon of sympathetic detonations in blastholes is investigated by comparing experimental observations and numerical modelling results. Numerical modelling using the TDL computer code and Forest Fire decomposition rates for commercial explosives has shown the importance of blasthole diameter, impedance of stemming material and host rock. Comparison with experimental observations has also shown that sympathetic detonations cannot always be treated as shock to detonation transitions (SDT). Examination of previous results which have been obtained from calibrated low amplitude shock experiments reveal that there is an ignition threshold prior to the detonation threshold. The difference between the two thresholds is more pronounced in the case of air bubble sensitized products. The ignition threshold can be very important under the confinement provided by the blasthole and the conditions of application. It also correlates well with the pressures expected at the gap distances of interest in the practical application. It is suggested that critical energies are used as the criterion for cross initiation in blastholes. Practical suggestions based on the numerical calculations and experiments based on these calculations are also given and discussed.

Jan 1, 1992

By John C. Didlinger, John L. Didlinger

As we begin the pre-blast survey we need to decide on the number of holes needed for production and a detailed highwall inspection. The survey consists of checking the highwall and placement of barrier cones. At the Elmhurst Chicago Stone Company, Barbers Corner Plant, we use 18-24" orange highway type safety cones. These cones are easily noticed because of their high visibility color in all weather conditions and are placed approximately 20-25 feet from the face and approximately 50 feet apart along the highwall, then the area is checked for back break, under cut, over hang, surface filled area and clay area. This deposit is unique because of the number of clay filled areas and slip seams that meanders through the deposit plus a fault that runs North-Northwest and South-Southeast. This particular limestone deposit is overlaid with glacial sand and gravel and the top weathered stone wanders plus or minus 10 feet in 1400 feet.

Jan 1, 1996

By Elias Poulakidas, Marco Arellano

The impact of a higher copper price on the open pit metal mining sector has derived in a faster and safer way in which the mining operation of broken and mineralised material is carried out. In this regard, a good control of bench stability allows a lesser extra removal of material and so more safety to get the planned ore. The stability is ensured through an efficient drilling and blasting, applying the current technology and available know-how. An efficient use of energy through low-density explosives which are the most adequate for the existing solid rock releasing energy in a smoother way through a deterministic detonation sequence which is the application experience presented here. This application experience has two main technological factors; the adequate type of explosive for the kind of rock, in terms of velocity of propagation (Vp) together with the use of a determined detonation sequence and the appropriate designs, which allow to reduce the level of damage to the walls and to maintain a minor backbreaking through quantification with vibration modelling carried out at the near field. The reductions achieved were 30% lower in peak particle velocity.

Jan 1, 2008

By Lee Wehner, Daryl Kin, John Bolger

The Maumee Quarry, located in the city of Maumee, Ohio, has large in-situ cavities, ranging in size from 3 ft (.91 m) in diameter to over 15 ft (4.5 m). The drill/blast team challenge is to drill, load and shoot the geologically disturbed rock in a safe, cost efficient manner, while in close proximity to a commercial area. A continuous improvement process, managed by a Blast Optimization Team (BOT), was implemented to quantify the innovative explosive loading techniques that have been implemented. Borehole camera monitoring, modified loading practices, the need for accurate drill hole logging and open communications between the drill and blast crew proves critical to the success of the operation. Safe Standard Operating Procedures (SSOPs) have been developed and are strictly enforced for the drill/blast cycle. All blasts are monitored with seismographs and recorded on video to provide detailed information as part of the Blast Management Plan. Despite the geological challenges, the measurement of rock fragmentation index versus loader dig rates has provided near optimal crusher throughput.

Jan 1, 2007

By Franklin J. A, Tam C. Palangio, N H. Maerz

WipFrag systems I, II and III have become the world standard in photoanalysis systems to measure particle sizes. Mines, quarries and excavating contractors can now easily measure blast results and track the progress of optimization efforts. This technology was developed and evolved ~to allow automatic measurements of the size distribution of particles on moving conveyors, in truck boxesand on crusher feeds. Production machinery can now be controlled by photoanalysis results and multiple cameras allow various locations to be monitored by a single system. Blast designs can, be monitored on a shot by shot basis. Changes in delay times, explosives, patterns and hole sizes can be quickly evaluated. Along with this measurement capability has come a heightened awareness of the importance of “optimum size” and uniformity of particles for lowest cost production and material handling efficiency. In the past, savings in the “drill / blast” cycle of the operation were sometimes overshadowed by downstream production costs related to fragmentation. Now total production costs can be compared with fragmentation sizes, which will immediately show the trend towards optimum size for economical production. No cost reduction program can be complete without this critical information.

Jan 1, 1998

By Lon D. Santis

This paper presents data and theorem to calculate the risk of experiencing undesirable lightning related events while blasting or while engaged in other lightning sensitive activities. The paper provides an overview of lightning hazards in blasting operations and a brief history of lightning related blasting accidents. Lightning continues to be the primary cause of premature initiations of explosives in mining; on average, over two such incidents are reported to the Mine Safety and Health Administration (MSHA) each year. The energy contained in lightning discharges and how this energy sets off explosives in mining is presented. Three categories of lightning warning methods: public media, lightning detectors, and atmospheric electrostatic field measurement are discussed. The remainder of the paper presents recently acquired data on the spatial characteristics of lightning development. This data is used to estimate the risk assumed by blasters under certain conditions. Risk estimations are made for electric and nonelectric blasting if persons are evacuated when cloud-to-ground (c-g) lightning approaches within a certain distance. For example, about 0.6% of all c-g lightning strikes have no other c-g lightning strikes within 25 miles in the previous 30 minutes. The paper shows that a typical blaster using nonelectric initiation in a high lightning density area with a 100% accurate lightning detector set to alarm at 25 miles would have a lightning caused unplanned detonation every 14,000 years.

Jan 1, 1998

By Cameron McKenzie

Flyrock is a complex issue involving interaction between the charging crew, the blast design, and the local geology, and once conditions on the shot meet certain criteria, the probability of a flyrock incident becomes unacceptably high. It is essential that flyrock awareness be built into the blast design process, requiring an engineering approach to understanding and controlling the outcomes and managing the associated risks. Based on previous studies of flyrock and published literature relating to fragment motion at high velocity in air, the equations to predict maximum flyrock range, and the size of particle achieving the maximum range, for blasts of varying rock density, hole diameter, explosive density, and state of confinement have been developed. These equations, and other associated correlations, permit the flyrock footprints to be established for any charge configuration, in any size blasthole, in rock of any density, and with particles of any known shape factor. The equations developed, and the mechanisms they reflect, allow engineers to go a long way towards understanding the primary factors controlling flyrock generation, including the rock mass, the blast design, and the quality of blast design implementation, i.e. the human factor. The paper presents guidelines as regards use of the equations to establish personnel clearance distances as a function of charge design and implementation, and equations to estimate appropriate stemming lengths when blasting must be conducted close to occupied or sensitive structures. The equations are amenable to definition of, and quantification of Flyrock Risk.

Jan 1, 2009

By Jim Daly

The word “Enron” has taken on a totally different meaning since its leaders were caught juggling the books, President Clinton’s reputation was destroyed not by what he did but by how he tried to cover it up, Martha Stewart spent time in prison for not being honest. Our society is tolerant of mistakes we humans make but has become very critical about what we do following those mistakes. The blasting industry is in a similar position. We have all heard the stories of the tree stump that came down through someone’s roof, of the windows that were broken, of the casualties that occurred when a blast was not properly guarded. What was done following these incidents? In the mind of the public, not enough.

Jan 1, 2007

By Courtney Vallejo, Rafiqul Tarefder

This study examines the effects of small scale airblast experiments on cohesive soils and the resulting ground vibrations and crater geometries. Relationships for ground vibration attenuation with soil depth and distance from the blast source were developed. The study is part of a broader research topic of understanding the vulnerability of earthen embankment dams to blast loading. Many earthen embankment dams in the United States were constructed more than fifty years ago and were not designed to withstand high-stress loading such as blast loading. These structures may be susceptible to failure and it is important to describe the response of the earthen dam during a blast event.

Jan 1, 2013

By J. A. Rodgers, K. C. Whitaker

The time domain during which an explosive detonates and causes rock to fragment and displace is on the order of tens of milliseconds. Because of this, the dynamic processes that occur during this time frame often become a source of confusion when trying to analyze the performance of explosive products in decked blast designs. As an illustration, the authors have experimentally examined explosives malfunction in decked blasts through state-of-the-art measurement techniques. The interaction of explosive products and blast geometry was examined in detail using the analysis of a series of decked blastholes. Explosive and initiator malfunction in decked blasts is often considered to be entirely the result of insufficient inert decking material, however, it is shown that rock properties and dynamic burden conditions may have a significant impact on decking performance. The successful application of deck-blasting technique for control of ground vibration amplitude relies on an understanding of the true dynamic performance of the blasthole.

Jan 1, 2000

By Richard J. Mainiero, Eric S. Weiss

This project investigates the behavior of blast waves from the detonation of high explosives in an underground mine. A series of explosive tests was conducted in the underground and surface facilities at the Bureau of Mines' Lake Lynn Laboratory to evaluate the potentially dangerous effects of blast waves produced by open shooting, blown out holes, or accidental detonations of explosives. Shots of C4 and TNT were fired at the dead end of a 6 ft high by 20ft wide entry, at the intersection of two entries, and on the surface. C4 and TNT were chosen for this research because they exhibit very consistent performance. Behavior of the blast wave was evaluated through recording of the pressure as a function of distance from the explosive detonation.

Jan 1, 1995

By Robert A. Cummings, Francis S. Kendorski, Charles H. Dowding

During the summer of 1980, a field project was carried out to determine the stability of the beautiful and dramatic natural limestone pinnacles (locally termed "Hoodoos") at Bryce Canyon National Park, Utah, when subjected to ground motions and airblasts resulting from proposed strip coal mine blasting. The concern arose from environmental considerations associated with the proposed development of a large coal strip mine which would approach within 4 miles of the park. The pinnacles range up to 150 ft in height and are quite slender, producing a fragile appearance. The remoteness and ruggedness of the area required a field camp, and 4-wheel drive vehicles, helicopters, and snowcats for support. Portable magazines were necessary to store the more than 7 tons of blasting agents and explosives required. In conducting the blasting, great attention was paid to environmental impacts. In the field, a target pinnacle was selected and instrumented with mechanical strain gages, and research seismographs that required helicopter placement.

Jan 1, 1982

By Jennifer Paukula, Steven Lindsay, S. Joon Kim

String loading is the placement of a bead or ‘string’ of emulsion along the lower edge of a development drill hole. The loading hose extraction rate controls the amount of emulsion placed in each drill hole. This allows a controlled distribution of explosive energy throughout the development round. Center holes are loaded using the slowest extraction rate causing the majority of the explosive energy to be placed in the center of the round. The loading hose is extracted successively faster for the buffer and perimeter holes causing less explosive energy to be placed near the edge of the blast. This causes less damage to the rock mass that remains in place after the development blast.

Jan 1, 2012

By Ashlin Pillay, Osamu Iwata

Hong Kong is ranked as the world’s third most important international financial hub and attracts significant growth and development annually. The city is also known as the world's most vertical city, the most common view from your window in Hong Kong city centre is probably the window of another 30 storey skyscraper. The increasing demand for real estate in this bustling Metropolis has placed immense pressures on its transportation infrastructure because whilst the construction continuously grows upward with larger and larger skyscrapers, it leaves the transportation planners with very little choice but to go underground. As a first world city, interrupting daily business operations is simply not an option; however, of even greater concern is the safety of these 8 million residents. Blasting Regulations are under the strict control of the Mines Division showing zero tolerance to the breaching of safety standards. The Ho Man Tin Station (HOM) excavation, a part of the Kwun Tong Line Extension (KTE) project situated in Hong Kong began in June 2012 and is one such project that is under strict regulations from the Mines Division. The HOM project is a cross cut interchange station between the Kwun Tong Line Extension (KTE) and Shatin Central Link (SCL).

Jan 1, 2015

By Raimo Vuolio

"Over the past 30 years, the Nordic countries have developed similar practices for estimating damage caused by rock blasting vibrations. However, over the last few years the risk of damage has sometimes been estimated by using international values, which have created unnecessary costs, since they are too conservative. This paper gives a proposal for Finnish blast vibration standards and a calculation model for the extent of the zones for building inspection, risk analysis, and vibration measurements. The international conclusion is that particle velocity is the best descriptor for limiting damage potential for structures. Over 900 000 vibration data recordings from 52971 blasts were collected for this paper during 1970-1989. They show that the most practical description is the vertical component of the peak particle velocity. As rock is a nonhomogeneous medium, it is hard to predict the need and scope of risk analyses, building inspection, and vibration measurements. As a large number of blasts were monitored for the recording of the peak particle velocity in several locations in Finland, and the data combined, it is possible to establish safe scaled distances for the calculation of the need and scope of risk analyses, building inspections, and vibration measurements."

Jan 1, 1991

By S K. Mandal, S Dasgupta

"Damage is classifi ed as loss in the integrity or deterioration in the quality of rock massand is infl uenced by methodology of excavation on the geo-technical properties of rockmass. Overbreak, on the other hand, is the result of damage and is quantifi ed in either of the terms viz., extra mucking, shot-creting, application of extra support system and extension of scheduled completion time. Damage or overbreak in rock mass by the impact of blasting, is generally unavoidable but, the magnitude can be minimized so that it does not deteriorate the quality or integrity of structure. The paper, here, analyses magnitude of overbreak of a powerhouse cavern with respect to different blast patterns implemented at the site. The magnitude of overbreak was analyzed in terms of profi le measurement with the help of laser profi ler and percentage of halfcast markings observed on the periphery rock wall. The paper revealed the impact of decoupling ratio, blast pattern and geometry of blasting patch on the magnitude of overbreak. The authors observed that presence of un-favourable joint pattern or foliation plane along the periphery rock wall couldn’t contain magnitude of overbreak within allowable limit. The analyses revealed that percentage of half-cast markings on periphery rock wall was infl uenced by response of rock towards detonation of explosive and cannot be a single parameter to assess the effectiveness of a blast. The analyses also revealed that magnitude of overbreak for down-stream wall was more than that observed in up-stream wall."

Jan 1, 2008

By John P. Ashby

Production blasting is a process of destruction of rock masses in order that ore may be extracted. Many open pit operations are faced with the apparently conflicting requirements of providing large quantities of fragmented rock for the processing plant and of minimizing the amount of damage inflicted upon the surrounding pit slopes. A reasonable compromise between these two conflicting demands may often be found by means of simple engineering of production blasts.

Jan 1, 1980

By F M. Dantini, P Berry

An experimental investigation on the trend of cratering induced by explosives placed on rock masses was carried out. By using various types of explosives and rocks having different geomechanical parameters, it was possible to evaluate the influence of the explosive-rock coupling. Furthermore, the importance of the parameters defining the rock and the explosive for the absorption of energy induced in the rock mass, is pointed out.

Jan 1, 1981

By Salah A. Taqieddin

Blast casting or trajectory blasting, as it is sometimes called, is an innovative mining technique that has been receiving increasing acceptance among operations of surface coal mines and quarries as a means of offsetting the rising cost of mechanical excavation of overburden with a high overburden-to-ore ratio. Many similarities exist between geological characteristics of overburden formations of phosphate beds and the formations that conceal coal seams. Both are sedimentary origin and are removed for mining in an identical manner (i.e. use of a dragline or shovel to strip or cast the overburden aside).

Jan 1, 1997

By Terry Nichols, Karl E: Warkwick Burgher, Charles J. Wideman

The application of Fourier spectral analysis to records of ground vibration generated by over 100 explosions from an open pit mine is used to develop empirical predictor equations that relate the response spectra to the blasting parameters used to generate the excitation motion. Time series representations of ground particle velocity are transformed into the frequency domain where the appropriate modifications are made such that the inverse Fourier transform yields the time series representation of particle displacement and acceleration. Compensations are made for the transform function of the recording system in the frequency domain. Spectral analysis of the three types of ground motion is correlated with the blasting parameters. The results show that the frequency content of ground vibrations generated from a mine blast can be quantified in terms of the predictor equations.

Jan 1, 1990