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By Virgil J. Stachura, Calvin L. Cumerlato

The U. S. Bureau of Mines is conducting research on blasting methods that reduce highwall overbreak and the associated rockfall hazards. This paper presents the results of tests using a low-density water gel to improve the quality of air-decked presplit blasts at a surface coal mine in New Mexico. The explosive's specific gravity averaged 0.50 and was bulk loaded using a modified truck which injected the gassing agent. Reductions in overbreak and resulting rockfall were achieved in comparison to a highwall presplit with ANFO. The test sections used 15° angled blast holes and resulted in 1,119 m (3,672 ft) of air deck presplit highwall using a low-density water gel which was then compared to 894 m (2,934 ft) of highwall shot with an ANFO air decked presplit design. The total quantity of explosives per hole ranged from 68 to 113 kg (150 to 250 lbs) and the 27 cm (10-5/8in) holes were 19- to 33-m (62- to 108-ft) deep on 5.5 m (18-ft) centers. Periodic visual examination and photographic surveys of the highwall test areas were used to document the amount of rockfall. In addition, laser profiles of selected sections were conducted to further delineate the damage and highwall contour differences.

Jan 1, 1995

By Timothy Stark

At present blasters are strictly liable under tort law for personal injury and property damage caused by ground vibrations and/or air overpressures. The application of strict tort liability to vibration and air overpressure damage has resulted in litigation that has hampered and probably will continue to hamper the blasting industry. There are many case histories in which blasters have been sued for the appearance of cosmetic cracking, some of which have involved frivolous claims and marginal expert testimony (Oriard 1999). This litigation has resulted in additional costs to the blasting and construction industries and the American public because there are usually many plaintiffs involved and each case is usually adjudicated separately instead of under a class-action format. It is proposed herein that blasters not be held liable for vibration or air overpressure damages unless their conduct is proven to be negligent. A number of reasons are presented for raising the legal standard from strict liability to negligence including: (1) improvements in blasting technology that allow blasting to be conducted without substantial risk of damage and if damage does occur it is likely to be cosmetic, (2) establishment of conservative ground vibration and air overpressure damage limits for typical structures, and (3) established industry standards for construction blasting.

Jan 1, 2002

By Jikai Rong Changai Liu

The dig instrument by blasting is a,new product we developed(See Fig. 1) It is an apparatus to dig hole at the ground. It is composed of combustor A, combustor B, charge pipe and shock head. Work characteristics of Combustor A are that combustion time is 1. 5 seconds, driving force is 725kg. Work characteristics of combustor B are that the combustion time is 1. 3 seconds, driving force is 460kg. After the combustor is ignited, the charge pipe is drived into ground immediately. Then, whole dig instrument is threw out automatically, but explosive in charge pipe is left in ground and blast in the twinkling. The diameter of vertical hole formed by blasting is 3cm to 60cm which is controlled according to engineering requirement. The maximum depth of the hole diged by using the dig instrument is 2M. It applies to blindage of single solidier in military affairs, and hole planting pole as well as sewer in civil use and so on. The two shots are charged in combustors to dig a hole. The maximum weight of shot is 490g, minimum is 130g. The whole process diging hole is completed automatically in about ten seconds.

Jan 1, 1998

By Diane F. Baker, Cathy Aimone-Martin

A series of small-scale explosive experiments were conducted in a perlite mine near Socorro, New Mexico. These experiments were a joint effort between Los Alamos National Laboratory, New Mexico Institute Of Mining and Technology, Southern Methodist University, and Defense Nuclear Agency. The purpose of these tests was to measure the changes in the shock wave and seismic coupling as a function of depth of burial and structural setting. The size of the explosive charges ranged from 1 to 68 kg. Over 1150 measurements of velocity and acceleration were made on thirteen experiments using three component sensors. The sensors were placed to maximize the azimuthal coverage as well as to provide data at a variety of ranges from ~1 to 130 m A few far field measurements were made at ranges of ~2Êkm. While the bulk of the measurements were made on the surface, high g accelerometers were placed in one instrumentation borehole to provide some free-field measurements. Preliminary results indicate that significant differences in the amplitudes of signals can occur when the location of the explosive charges are changed by only meters. Part of the observed difference is attributed to variations in the rock immediately adjacent to the charge affecting the shock coupling; and part to the effects of the site characteristics.

Jan 1, 1994

By J. Sigler

A series of small scale tests have been performed to establish the effect of powder factor and initiation timing on the grindability of rocks. The blasts were performed in high quality granite blocks, which were cut from stone prepared by dimensional stone quarry operations. Three different types of granite were tested. The charge configurations included detonating cord placed in five holes with water as a coupling medium or concentrated charges of equal mass, placed in the same number of holes, fully stemmed or air decked. The powder factor was varied from 0.4 to 1.2 kg/m3. Typically all charges were detonated simultaneously; however, in some experiments, detonation waves collided in the middle of each borehole and in others a small delay was used between charges. All fragments were collected and screened, and drop weight impact tests were performed on selected size fractions, using different impact energy, to calculate the resistance of the rock to impact breakage. The work index of some of the blasted samples was measured using a standard Bond mill arrangement. The experiments generally showed increased softening of the rock with powder factor, which appeared to be the dominant factor. Charge configuration as well as in-hole collisions of detonation waves affected the initial fragmentation but had little effect on the impact breakage of the samples.

Jan 1, 2008

By C. Lownds, U. Steiner

In 2008 a paper from the same source describing four actual cases of exposure of electronic detonators to lightning strikes was presented. It was shown that electronic detonators, like other initiation systems, are vulnerable to very close or direct lightning strikes. At the time of submitting this abstract no further incidents with lightning have been experienced. As a result of those original incidents, and in order to understand how the safety devices inside electronic detonators break down, two series of tests have been done, each with 2 detonator designs. In the first series detonators were subjected to capacitor discharges up to 6kV and 1kJ in energy. In the second series the intensity was increased to 800kV and 24kJ in energy. In the second series, more electrical energy was delivered to the detonator assembly than the explosive energy of the detonator. In both series both detonators showed a spectacular ability to resist very high discharge energies. The tests are described in detail with supporting photographs. The data for both pin-to-pin and pin-to-case (more relevant to lightning) are presented and discussed. The mechanism of breakdown of safety devices is now understood better and the learning is being used to design more robust products. This high-voltage testing is relevant in understanding how electronic detonators might initiate as a result of a very close or direct lightning strike 1. Orica

Jan 1, 2009

By Braden Lusk

This paper includes results from analysis of recorded Acoustic Responses of Structures to Blasting. The analysis was performed to determine specific characteristics of sounds experienced inside homes during blast events. Data was collected in a typical house within the Boone North No.2 Coal Surface Mine in Ashford, WV which was instrumented for several blast vibration and acoustic responses. The instrumentation consists of four acoustic microphones distributed throughout the internal areas of the house and three geophones buried near the house. Two additional channels collect the trigger signal and Air Blast information. For each blast event recorded by the system, the mine blast reports were used to obtain major blast characteristics such as distance from the blast to the instrumented house, weight of explosive used, number of boreholes, delays, and other important parameters. This information allowed study the relationship between the acoustic response and the blast design. From a database of 43 records, five records were chosen for complete analysis. These records were chosen based on distance from the blast to the house, and specific blast parameters. This paper presents the result of the relationship between the frequencies and amplitudes for the entire trace of acoustic records, the response due to ground vibration (GV), and the response due to air-blast (AB). Frequency content was obtained through Fast Fourier Transforms (FFT), using D-Plot software. The records have a typical shape that permits cutting and analyzing each part of the signal with respect to GV and AB separately. Some conclusions are reported concerning the relationship between blast parameters and acoustic response of structures.

Jan 1, 2009

By Leslie Taylor, Kevin Genson

This paper reports on an experimental study of the effect that bottom shaping might have on the impulse delivered to a light armored vehicle due to a buried mine detonating beneath the center of it. The study was restricted to explosives buried in saturated sand and three parameters were varied within the study: bottom angle (0 degrees to 21 degrees), depth of burial of the explosive (1.02 mm to 12.7 mm), and stand off distance (0 mm to 38.1 mm). Six hundred and thirty six milligrams of explosive was used as the explosive load. It has been shown in previously published work [1,2] that Hopkinson scaling works well for the determination of impulse loading on a semi-rigid target plates. Therefore in terms of a full scale test using 4.54 Kilograms of explosive the parameters investigated would cover a DOB of from 19.56 mm to 243.84 mm and a Stand off distance from 0 to 734.06 millimeters. These values nicely cover those of interest to the Marines with regard to the AAV (amphibious assault vehicle). Four angles were investigated at all DOB’s and Stand off distances – 0 degrees, 7 degrees, 13 degrees, and 20 degrees. The results show that reduction in impulse delivered to the target is achieved with an angled bottom on the target plate with a major reduction occurring before the 13 degree angle is reached. Hence vehicles with quite modest bottom angles could help greatly in load reduction with very little loss in utility.

Jan 1, 2008

By Robin L. Simmons

Mining in the Genesis open pit has been conducted above the active haulage and ventilation declines of the Deep Star underground mine. Production has continued in both mines. The Deep Star haulage and ventilation declines, the primary and secondary egresses respectively, had to remain open and safe for travel until the new haulage and ventilation accesses were completed. Eventually, the upper 350 feet in each decline will be removed. The declines are in relatively competent calc-silicate hornfels with several high-angle, northeast-striking, clay-filled or open-spaced fault zones that create localized areas of poor ground requiring steel sets. To maintain the integrity of the declines, blast-induced vibration levels and damage were monitored in both declines after each surface blast. Seven geophones were installed in the declines to monitor peak particle velocity and peak vibration frequency. These data helped design subsequent blasts and predict expected vibration and damage levels. Blast design modifications included reducing the pattern size, reducing the powder factor and limiting blasthole detonations per delay. While limiting blast-induced vibration, these blast design modifications had to allow effective surface mining to continue. Linear regression analysis of peak particle velocity and scaled distance was used to determine the scaled distance necessary to keep the peak particle velocity under 2 inches per second. To date, the new ventilation raise, which is also the secondary escapeway, has been established and safe conditions were maintained in the original ventilation decline. Data collection and conscientious blasting procedures continue above the haulage decline.

Jan 1, 1998

By Thomas A. Gelormino, Ulrich La Fosse

"Deep blasting was used to densify foundation soils for a large manufacturing facility inChicopee,Massachusetts. A 360,000 square foot building, whose construction began inthe summer of 1990, is founded on alluvial deposits up to 90 feet in depth. These deposits are comprised of saturated very loose to loose fine to medium grained sands with traces of silt and gravel. During the building foundation design it was found that to withstand earthquake forces without soil liquefaction, it would be necessary to improve portions of the alluvial deposits by densification. The zone in need of densification extended from approximate depths of 20 to 50 feet. Several conventional densification methods, including vibrocompaction and deep dynamic compaction, were evaluated along with deep blasting. Detonation of 1-3/4 inch diameter charges of 65 percent gelatin dynamite (Atlas Power Primer) installed inside 2-inch diameter PVC casings to a depth of up to 40 feet, was used to achieve the desired densification. This method was selected over others due to its lower cost and decreased construction time. Although used in New England once in1940 for a dam and once in 1960 for a transmission line tower to improve foundation soils, there is no precedent found in the literature for densification by blasting to improve liquefiable soils below a proposed building. Details of a test program and the production blasting, including vibration data are presented. Pre-and post-blasting data conclusely shows an increase in the density of the sand deposit after blasting."

Jan 1, 1991

By Y. Hirosaki, H. Hamashima, Y. Itoh Kato, S. Tanaka

The emulsion explosives show non- ideal detonation behavior, and its detonation velocity can be controled by selecting the size and adjusting the quantity of voids involved. To establish the technology to control the detonation characteristics of the emulsion explosives, some experiments have been carried out using resin balloons of five different sizes ranged from O.OSmm to 2.42mm in the average diameter. Detonation velocities of the emulsion explosives containing resin balloons of different size and quantity were determined for the charge diameter of 20-50mm. The detonation velocity at infinite charge diameter was compared with calculated ideal detonation velocity. The emulsion explosives containing large (0.5mm or larger) balloons showed big discrepancy between the measured and calculated detonation velocities, and the fraction of ammonium nitrate reacted in the reaction zone was estimated to be significantly low. It was shown that the reaction zone length was proportional to the size of voids involved. The critical charge diameter was determined for the emulsion explosives containing different resin balloons at the various explosive densities. It is large for the emulsion explosives containing large voids, and it was shown that the critical diameter is proportional to the distance between the void surfaces, not to the void spacing, the distance between the centers of the voids. The reaction rate of the bulk emulsion matrix seems to be the major factor that affects the critical diameter than the specific surface of voids. Good relationship between the critical diameter and the reaction zone length was observed.

Jan 1, 2000

By Lewis L. Oriard

Ground vibrations associated with blasting are generally in a higher frequency range and of shorter duration than those generated by earthquakes, and the intensity scales for earthquakes cannot be applied directly to blasting vibrations without modification. Further, the profession does not need an intensity scale merely to estimate vibration intensity. If the blasting in question was not monitored instrumentally, it is a simple matter to estimate the range of intensities based on published prediction formulae or data from various sources such as Oriard (1), Nicholls et al (2), Hendron and Oriard (3), Siskind et al (4), and others. However, the profession has a serious need, for purposes of evaluating damage claims, to understand the relationships between vibration intensities and the levels of observed effects. The criteria for threshold damage do not apply to typical cases which usually involve structural damage. If the damage in question would have required ground vibration with a particle velocity of, say, 20-120 ips, damage is not verified by showing that the vibration merely approached a suggested limit to avoid threshold damage. That is not the question. This paper provides some guidelines for comparing severity of damage to intensity of vibration which would be required to cause such damage, much as is done when determining earthquake intensities. In addition, this paper includes a discussion of strain amplitudes induced by environmental forces, the predominant causes of damage to structures. Also, certain popular myths regarding blasting damage are discussed in the paper. Due to space limitations, the paper will not include a discussion of airblast effects.

Jan 1, 1989

By Sehoon Lee, Duhwoe Jung, Eunsu Cha, Kyeonghwan Jeong

This case study presents the effectiveness of underground rock blasting to facilitate the trench cut in the hard rock layer using a conventional trench cutter for the construction of a diaphragm wall. Rock blastings are pre-performed up to the scheduled depth and then the fragmented rocks can be easily cut using a conventional trench cutter. Two trial underground rock blastings have been performed and the effectiveness of pre-blasting is presented in terms of a cutting rate, a loss of cutter heads and an amount of overbreak. Based on the results obtained from the trial underground rock blastings, the following conclusions can be appropriate: 1) A pre-blasting of hard rock layer located in depth can help to overcome the limitation of the trench cut using a conventional trench cutter. If the hard rock layer is fragmented after blasting, the fragmented rocks can be easily cut using a conventional trench cutter, 2) The speed of cutting works was accelerated and the loss of cutter heads was significantly reduced in the sections where the blastings were applied prior to cutting. 3) The amount of overbreak, expressed in terms of the amount of poured concrete, can be reduced to some extent. However, the location of blast holes in the trench can also contribute to the amount of overbreak. The closer the location of blast holes to the edge of the trench, the more extensive fractured and cracked zone can be formed on the face of the trench. This can increase the amount of overbreak if the trench is left empty for a while.

Jan 1, 2000

By Norman Paley, John Kells

The climate and location of the Red Dog Mine present several challenges to blasting operations. The mine is located north of 68º latitude, in an area of continuous permafrost. Ground temperatures are below freezing year-round and air temperatures range from -40 to 70°F (-40 to 20°C). Because there is no overland access to the mine, the entire year’s supply of bulk explosives, approximately 7,000,000lbs (3,175,000kg) is shipped in by barge during the 100 day shipping season when the port is ice-free. The first week in July is the earliest that new product arrives at the port. Emulsion usage is maximized from mid April through October when surface water fills the blastholes during drilling. This necessitates that a considerable portion of the bulk explosives are stored for 10 months or more before usage. The emulsion is routinely pumped from the ISO containers at temperatures of 20ºF (-7°C). The mine engineers conducted a testing program during the 2001-2 blasting season to identify the bulk explosives best suited for the conditions at the mine. A secondary goal was to decrease the usage of sensitized emulsion, as this is the most difficult portion of the explosives order to ship. To ensure repeatability when transferring the results to the day-to-day blasting operation, the majority of the testing was incorporated into normal blasting operations in the field. The mining methods used at Red Dog Mine make direct fragmentation analysis impractical and performance testing in the field relied primarily on VOD measurements. The products were also tested for their ability to be pumped in cold temperatures.

Jan 1, 2004

By Ruilin Lang

This paper presents an application of 3-D plots and non-linear regressions to define a sitespecific form of the charge weight scaled distance. The PPV (PPA) of single hole blasts is normally considered as a function of two independent variables - the charge weight and the distance. It is of great importance to obtain the relationship of the function accurately for a concerned site in terms of blast vibration analysis and modeling. However, in pre-computer time it was difficult to plot 3-D graphs. Consequently, a charge weight scaled distance was used to plot the PPV (or PPA) against the scaled distance as 2-D graphs. Blast vibration investigators use several forms of the charge weight scaled distances to plot data. We can exemplify them with the cube root of charge weight scaled distance, the square root of charge weight scaled distance, and other forms (Hossaini and Sen, 2004). Each of these scaled distances assumes relative contributions of the charge weight and the distance to the vibration attenuation. For example, the charge weight is assumed to have a less contribution to vibration in the cube root scaled distance than it is assumed in the square-root scaled distance. In reality, for different sites the relative contribution of the charge weight and the distance may be different and site-specific. This may explain that in some cases, the blast vibration data plots using these charge weight scaled distances are scattered. This could be largely due to the fact that the definition of the form of the charge weight scaled distance is not adequate for the particular site condition.

Jan 1, 2006

By Cathy Aimone-Martin, Kristin Dunlap Kolden

Blasting was conducted for the Army Corps of Engineers (Corps) in the Columbia River near Saint Helens, Oregon during 2009 and 2010 to deepen the navigation channel as a final phase of a dredging project to accommodate larger container ships. The Columbia River Channel Improvement Project (CRCI) required 4 months to blast and dredge 300,000 yd3 (229,366 m3) of basalt from the bottom of the channel to allow Post-Panamax vessels with drafts up to 50 ft (15.2 m) access to the Ports along the River. Explosives charges were limited to 90 lbs (40.8 kg) per delay for the protection of fish and marine life in the area. A fish mortality study and marine mammal monitoring program was also required by the Corps. Underwater overpressure monitoring was required for each blast and peak overpressures measured 10 ft (3.1 m) above the river bottom 140 ft (42.7 m) from the closest blast hole were not to exceed 70 psi (483 kPa) with a cautionary level of 40 psi (276 kPa). Specifications required sampling rates of 500k S/s and PCB Peizotronics tourmaline pressure sensors. The Corps granted permission to co-locate additional ceramic-type sensors at different sampling rates to design redundant monitoring systems 140 and 300 ft (42.7 and 91.4 m) from blasting and develop a site-specific overpressure attenuation model for the project. This paper presents the correlations of overpressure with cube-root scaled distance factors, a comparison of measurements using three different pressure sensor systems, and a discussion of blast design influence on overpressure measurements.

Jan 1, 2014

By Robert C. Fouchard, Gordon Chalmers, David E. G. Jones, Ivana Alilovic, Phillip D. Lightfoot

There have been numerous international instances over the last several years in which pumping emulsion explosives has resulted in accidents, apparently as a result of increased thermal sensitivity under these conditions. The key questions for the explosive industry are (1) what are the parameters that influence the sensitivity of emulsion explosives and, (2) how do these various parameters interact. To address the sensitivity of emulsion explosives to various parameters, a study was undertaken using an accelerating rate calorimeter (ARC) and a heat flux calorimeter (HFC). The effects ofthe addition of ammonium nitrate (AN) prills and different grades of aluminum (Al) on the thermal behaviour of emulsion explosives were determined. Additionally, changes in pressure, atmosphere (inert or oxidizing) and sample vessel material were assessed for their impact on thermal sensitivity. Addition of AN prills, fine granular Al or atomized Al did not affect the onset temperature for exothermic decomposition, so that the maximum “safe” temperatures for emulsions containing these additives will be similar. There were differences in the rates of self heating, however: AN prills decreased the rate of self heating, whereas atomized Al increased it. The emulsion formulations containing atomized Al produced small holes in titanium vessels. This phenomenon did not occur in Hastelloy C vessels, providing a reminder that materials of construction need to be carefully considered for equipment used to manufacture or handle emulsion explosives.. Both ARC and HFC experiments gave lower onset temperatures in air than in argon. We attribute this to oxidation of the oil phase by air. This result is significant for dry-running pumping conditions, where emulsion is heated in the presence of excess air.

Jan 1, 2000

By Piyush Rai

Proper use of fi ring pattern vis-à-vis the blast requirements can provide optimal blast performance in terms of fragmentation. Further to this, each fi ring pattern has its own characteristic, for instance, although V-type and diagonal fi ring pattern provide same Se/Be ratio, the V-type fi ring pattern increases the opportunity for in-fl ight collision amongst broken rock fragments during their movement. Similarly straight V-type and skewed V type fi ring patterns (V1,V2 etc.) have their own characteristic strengths and weaknesses. In this light the present paper highlights the application of three different types of fi ring pattern on two different type of sandstone overburden benches of a large coalmine in India. The study reveals that Firing pattern infl uences the effective spacing to burden ratio at the time of detonation. By changing the fi ring pattern, effective burden (Be) changes and the ratio of effective spacing (Se) to effective burden (Be) during the fi ring is also subject to change in comparison to drilled spacing to burden ratio (S/B) Hence, the Se/Be ratio vis-à-vis fi ring pattern must be used to design the blast rounds. The results have been derived on the digital image analysis based fragment size characterization, excavator performance and evaluation of powder factor values on blasted muck piles. Skewed V- type fi ring yielded the best results in comparison to straight v-type and normally practiced diagonal fi ring pattern on the moderately strong sandstone benches, whereas, the existing diagonal fi ring pattern appears to be satisfactory on weak (weathered and gritty) sandstone benches. The presence of geological anomalies has also been investigated.

Jan 1, 2008

By AJ Rorke

Blasting trials using Daveytronic Electronic Delay Detonator systems (EDD’s) were conducted at the Alpha Ferro Quany (Pretoria) and the Eikeboom Colliery near Witbank in November 1999. The objectives of the trials were to determine the influence of accurate hole firing on rock fragmentation, blast-induced vibration and blast throw. This paper provides an outline of the trials and an analysis of the results. The results were compared with a normal shock tube initiation system. Fragmentation was measured using video-imaging techniques at the hard rock Ferro Quarry for one conventional shock tube blast and two EDD blasts. No significant difference was measured in the fragmentation between the shock tube blast and the two electronic detonator blasts. Joint planes mostly defme the fragments at Ferro Quarry. The fragment sizing was therefore controlled mainly by the rock structure and the blast timing appeared to have no influence. Vibration measurements made at Ferro Quarry indicate that electronic detonators have a marked effect on vibration frequencies compared to shock tube systems. The more accurate detonators resulted in a narrower f+equency band at lower amplitude with similar timing. By modifying the blast timing, the dominant frequencies were changed. The electronic detonators had a significant positive influence, therefore on blast vibration and its control. The timing scatter measured from the shock tube blast was considerable, with measured inhole detonator scatter at 48 ms over a sample of 19 units. Surface delay periods less than 42 ms would therefore not be able to provide effective sequential firing. The scatter of the Daveytronic units was below the 2 ms resolution of the high-speed camera used to film the blasts. Reliable sequential firing, even at very short delay intervals was considered the main reason for notable improved throw in an overburden blast at Eikeboom Colliery. Blast throw was improved by 25% for the test blast.

Jan 1, 2000

By Dae-Woo Kang, Sang-Wook Kim, Shin Lee

The Air-tubes blasting method is provided in which a series of aligned boreholes are charged with explosive s and air tubes in a predetermined blasting pattern. The air tube is composed of cylindrical flexible tubes which have a predetermined width and length to be fit with the site boreholes. Within a preferred formation, each borehole is charged with the explo sives and detonators with an air tube installed just above the explosives. Stemming materials are filled above the air tubes. At the limestone mine of Sung-Shin Cement Co., in South Korea, these blasting tests were performed by a diameter 102 millimeter and 15 m long boreholes with the charging length of explosives was 8m to 10 m by the total weight of explosive 40 to 50 kg with 3m to 6m air tube which has a 76 mm diameter, and 1m to 3m stemming cover. Blasting results showed the about 10% to 30% explosives savings available and especially, the about 20% to 50% reduction of ground vibration with the low noise measures around 2dB to 5dB by this new blasting method which was compared with the conventional blasting methods. The explosives and air tubes may be alternately charged along the boreholes. The use of air tubes which were charged above an explosive layer allow to form the quantitative air decking in every blast hole. Therefore, the Air-deck effect can be easily obtained through this blasting method, and also easy to increase the fragmentation rate resulting in the more suitable mucking procedures at the working site with the minimum usages of explosives for the better economic operations in mine quarries.

Jan 1, 2005