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By Michael Wieland

Sharp transient stress waves generated during the delay blasting of underground coal can damage unfired borehole charges remaining in the delay pattern. These tremendous stress pulses in coal bear a strong resemblance to underwater shock waves, despite differences in rise times, damping rates, and scaling relations. "Shock wave" terminology is adopted to distinguish the sharp transient waveforms propagating through the coal from the gas-driven stresses that rift the coal. Reported waveform characteristics of shock waves through underground coal were utilized to design a simulator test for rating the impact resistance of cap-sensitive explosives. Theoretical minimum borehole separations were determined for each cap-sensitive explosive from the requirement that worst-case waves hitting an unfired charge would not exceed its impact resistance rating. Rugged explosives have higher impact resistance and will function properly at smaller borehole separations. Additional work is required to verify the findings from the simulator technique and modeling relations reported here.

Jan 1, 1990

By Ruilin Yang

This paper presents a fragmentation model for large production blasts. The model uses peak particle velocity (PPV) induced from the blast as a controlling parameter to predict the fragmentation size distribution. The PPV can be related to shock pressure or strain under a given rock condition. The fragmentation size is calculated at three-dimensional grid points within the blast volume. The grid size defines the calculation resolution of the model. The fragment size distribution is assumed to be in the same form as the crack distribution within a cube (of the size equals to the grid size) surrounding a grid point. The crack distribution in rock from impact is based on the finding from previous researchers (Seaman et al., 1976). The fines and oversized blocks are calculated explicitly. The summation of the size distribution at all calculation grid points over a specified volume of the blast yields an overall size distribution for the volume.

Jan 1, 2015

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 Dean E. Albon

The author gives a brief resume of his observations of drilling and blasting supervision in surface coal mines during the past thirty years and recommendations for upgrading this supervision to the category of a professional.

Jan 1, 1979

By P D. Katsabanis

Explosives malfunction due to shock waves is a serious concern for successful blasting results. Malfunction includes sympathetic detonation and desensitization of explosive charges as well as the modification of firing times of conventional pyrotechnic detonators.

Jan 1, 1995

By Clive-Workman Davies, K K. Kabongo, Mensah Frimpong

Given the capital intensity of the dragline operation coupled with rising cost of explosives, the onus is on mine operators to make maximum use of explosives in blasting to assist dragline diggability. At a surface coal mine in South Africa large boulders necessitating secondary breakage and in some cases completely unfragmented sections of a blast resulting in low dragline diggability were encountered in the interburden blast. Twelve blasts were therefore closely monitored and dragline productivity evaluated. The ultimate aim was to improve the overall blasting performance and hence increase dragline productivity. Three areas were in focus; fragmentation assessment, dragline productivity assessment and cost analysis. The studies indicated unsatisfactory explosive and initiation performance, problematic blast design and questionable operators performance. It is established that dragline cost account for 60% of the total mining cost whereas the drilling and blasting cost account for the remaining 40% and that improvement in dragline productivity results in automatic cost saving.

Jan 1, 1996

By M Siefert, P Moser, T Oberndorfer

"The EC-project ""Blasting Control"" with partners from France, Austria, Italy and Greece dealt with the development of a diagnosis system, which enables blasting experts to investigate in detail on probable reasons of poor blasting results in underground drifting. The system incorporates monitoring of geometric, explosive, vibration and granulometry data. All data are compiled in a database and are provided for direct retrievement by demand of the experts in a graphical environment. This paper focuses on the advantages of such graphical system for both research tasks and applications in real testing situations. It describes the procedure of monitoring and presents a selection of graphical outputs generated during data processing immediately after blasting. Benefits of detailed monitoring in respect of detecting sources of errors are explicated by a actual example of a test series in a mine. The paper will conclude with an outlook onto the scientificresearch work which is planned to be based on the results of hitherto investigations."

Jan 1, 1996

By Claude Cunningham

Simple bulk energy rating of explosives obscures the realities of how these deliver their energy, and diverts attention from the key question of controlling blasting results. Explosive performance is directly related to the pressure pulse impacting on the blasthole wall. This is helpfully visualised by comparing the adiabatic expansion plots for explosives of interest on the right scales and axes. The simple comparison of a pure emulsion with pure ANFO illustrates the practical significance of the intrinsic behaviour of these opposed formulations, showing that the emulsion can be expected to work more by softening rock, while ANFO will tend more to crack it. The explanation for these differences lies in the high shock, low sustained pressure of the former relative to the latter. The technique is readily applied, if a good detonation code is available and able to swap data into a spreadsheet. Any differences between codes will emerge most strongly in comparing the gamma plots.

Jan 1, 2002

A case history is presented where a variance was permitted by the court to change a 500 foot limit to 250 feet for blasting overburden at a surface coal mine in the proximity of a historic structure.

Jan 1, 1991

By Jean A. McIntyre

The Office of Surface Mining (OSM) has twice proposed rules for a blaster training and certification program to implement Sections 515(b)(15)(D) and 719 of the Surface Mining Control and Reclamation Act of 1977.

Jan 1, 1980

By N K. Jain, Rajesh Jain

This article has been written indicating the present trend in Blasting all over the World, so as to help in planning production and development of Industrial Explosives for the development of industries in all the countries in general

Jan 1, 1992

By Wiliam Reisz

As we approach the peak season for thunderstorm activity it’s important to keep in mind that lightning still poses a serious threat to drilling and blasting operations. Lightning remains the number one cause of accidental detonation of explosives.

Jan 1, 2008

By Alain Duchesne, Dominique Fonfrede, Alan Broca

The technique involves the removal, in one piece, of an unwanted concrete pile section, exploiting the principle of crack propagation induced using gas pressure. The device, or pod, is made of a container in which an over-pressure is generated. After a predetermined time delay of 72 hours, gas and pressure are produced by the reaction between a calcium base chemical and water.

Jan 1, 2012

By R Heater, G Glynn

Various small diameter commercial grades of slurry and emulsion explosives were tested and compared. Velocity diameter curves for confined and unconfined charges were established and the effects of temperature and hydrostatic pressure on critical diameters and minimum primer weights were determined.

Jan 1, 1984

By Robert Hopler

Complying with our request in the February issue of the AGRICULTURAL BLASTER for items that would be of interest to other blasters, Mr. Thomas H. Benton of Tennessee sends us an article in which his methods of securing contracts are explained:

Jan 1, 2013

Many North American coal strip operations are practicing trajectory control blasting with good results, often based on trial and error methods. This study summarizes the basic technical requirements for the design of bench-type casting with explosives to achieve further improvements.

Jan 1, 1987

By Miie Shields, Ed Billington

Trail blasters for the National Park Service (NPS) live and work in remote mountain terrain throughout the western states, where any support or resupply may be sporadic and ditlicult and mountain weather affects every activity. Mechanical “aids” are the pick, shovel, rock-bar, wheelbarrow, and a Pionjar or Cobra dritl. The blaster is usually faced with an extraordinary range of work, t?om delay blasts in weathered rock using driiole depths of 18” (46cm) to as little as 4” (1 Ocm), through reducing boulders and talus fields to useable tread, blasting stumps, snags and log-jams, to the explosive disintegration and casting of animal czcasses. One day he/she might provide a 500cf (14 cu meter) anchor excavation for a suspension bridge, the next day directionally fall 60” (1.5m) diameter snags in a camp area, and the following day blast a 3-foot-wide (1 meter) tread bench across a steep bedrock slope. To be effective, the blaster must design each and every blast around desired end result, crew and public safety, maximizing effective use of limited quantities of explosive, and the minimnation of environmental effects. Since almost all drillhole blasting occurs in the weathered zone of the rock, blasting is more the art than the science of judging rock density, hardness, cohesion and prefracturing, and selecting explosives, drill and delay patterns, and loading techniques responsive to those conditions. For these reasons the NPS issues its own Blaster’s License, with a basic requirement of at least 40 hours of NPS blaster training and 3 years of supervised Blaster in-Training experience. The focus of this pre-license requirement is on safety and using explosives as a precision tool, versus just “blowing things up”.

Jan 1, 2002

By Catherine T. Aimone-Martin, Elena Oana Jacobs, Brent Meins

Accurate pressure measurements during underwater detonations are critical for the protection of structures and mitigating impacts to fish and marine mammals. Current guidelines that limit underwater pressures are based on past studies, many of which used sample rates of 48 and 65 kS/s (48,000 and 65,000 samples per second). These sample rates may be insufficient to accurately record high frequency, sharp rise time blast pressures. As such, pressure thresholds associated with fish and marine mammal injury or mortality may be underestimated, calling into question the pressure and sound pressure level guidelines that govern underwater blasting today.

Jan 1, 2019

By Larry R. Fletcher

Excessive flyrock, which is blasted rock that travels beyond the secured blast area, is responsible for 25 pct of the blasting injuries that occur in surface mining. Excessive flyrock is also a frequent cause of damage to mine equipment and facilities.

Jan 1, 1986

By Jay P. Tobin

This paper will address the legal standards applicable to construction blasting lawsuits and offer best practices suggestions for pre-blast inspections, documenting the construction blasting work, recordkeeping, and effectively participating and partnering in the defense of a construction blasting lawsuit.

Jan 1, 2015