2021 Blasting Studies Target Common Challenges

Four studies on blasting optimization and blasting vibration damage disputes seek ways to attain best outcomes

by jesse morton, technical writer

Some of the top studies on blasting from around the world from 2021 show how mines and researchers are trying to solve timeless blasting challenges. While some of the studies may have been conducted on the other side of the globe, the problems they attempted to solve could occur at surface mines anywhere.

Two of the studies reviewed process optimization programs. A coal mine in India experimented to determine the big factors of overbreak. A coal mine in China tested presplit blasting at improving gas drainage and seam permeability.

Two of the studies looked at ways to prepare for blasting vibration damage claim disputes. Researchers in the U.S. looked for commonalities in two cases that were ultimately won by miners. And researchers in Vietnam trialed a cloud-based solution at remote monitoring blasts for the purposes of recordkeeping in compliance with government regulations and answering damage complaints.

All of them offer advice worth considering by those seeking the best overall outcomes when blasting.

Dispute Resolution in US

A study¹ that looked at investigations into complaints of blast vibration damage to properties near mines found that the records kept by the miners on the blasts ultimately exonerated the mines. Specifically, blasting records and the data from nearby offsite seismographs proved that the blasts could not have created airbursts or vibrations big enough to do the damage alleged.

The study looked at two investigations. One was into the allegations of a property owner near a coal mine in West Virginia. The other was into allegations of a property owner near a coal mine in Virginia.

In the first, the structure was a double-wide nine-year-old home on cinder blocks with concrete footers, and an external garage of similar construction. The allegation was filed in January 2020.

The reported damages included cracks in the drywall, foundation blocks, garage floor and driveway. Also reportedly damaged was the ceiling trim and a French door.

The West Virginia Department of Environmental Protection (DEP) “inspected the mine, reviewed blasting records, viewed the alleged damages, and issued reports dated May 20, 2020, and August 20, 2020,” the study said.

The DEP “review of the pre-blast survey showed that some of the damage was preexisting. It included a renovation survey due to recent upgrades to the home,” it said.

The nearest, most recent blast was 1,076.25 m (3,531 ft) away.

“The shot used 719.39 kg (1,586 lbs) of explosives per 8 ms of delay. According to the predictive equation, the home would have had a peak particle velocity of 0.003 m/s (0.127 in./s),” the study said. “The largest, most recent blast used 1,142.6 kg (2,519 lbs) of explosives per 8 ms of delay and was 1,373.4 m (4,506 ft) from the home. The predictive equation indicated that the home would have had a peak particle velocity of 0.003 m/s (0.119 in./s).”

The highest estimated airblast was 121 dB.

The limits set by the federal government are an “amplitude of 0.0127 m/s (0.5 in/s) for ground vibrations when frequencies are low (<40 Hz), and 133 dB for airblast.”

Therefore, the department concluded “the alleged damages did not meet the criteria for blasting damage,” the study said.

The U.S. Deparment of the Interior, Office of Surface Mining Reclamation and Enforcement (OSMRE), looked at the same information items and found the DEP determination was “reasonable and appropriate,” it said.

Ultimately, it was the company blast records and offsite seismograph readings that exonerated the miner.

In the second case, the house was built roughly a century ago as part of the Exeter Coal Camp. It was remodeled in 1975.

A contractor was doing the blasting from February 2019 to March 2020. “On January 29, 2020, the Virginia Division of Mined Land Reclamation (DMLR) requested technical assistance from OSMRE concerning a long-running blasting complaint alleging damage to a residence,” the study said. Numerous complaints were made throughout 2019.

The alleged damage included doors settling and needing to, first, be lifted to be opened and, then, later being removed entirely; vertical drywall cracks; uneven and warping floors; and soft spots in the yard due to alleged subsidence.

The “assessment was based on the company’s permit information, blasting logs, blasting seismograph records, a pre-blast survey, and an inspection of the residence and the mine,” the study said. OSMR found that “blast records were complete and critical information on the charge weight per delay in the blast reports was accurate.” There were, however, some errors within the records, but they apparently had no bearing on the investigation.

OSMRE put all the data from the blast logs and the seismographs into an EXCEL spreadsheet.

Findings included “the highest estimated vibration level at the residence had been 0.005 m/s (0.20 in./s) with frequencies of about 10 Hz,” the study said. “This was insufficient to cause any of the alleged damage, including cracks in masonry, concrete, or drywall; door settlement; floor rolling or warping; or the fallen vinyl soffit,” it said. “The highest estimated airblast at the residence was 127 dB, which carried no damage potential. Window breakage was not alleged.”

Further, the property had not been “undermined, and movement or unevenness of the ground was not due to subsidence or blasting,” the study said.

The investigator reported that “blasting conducted by the drilling company had not generated ground vibration or airblast levels in excess of the (government) limits,” the study said. “The investigator determined that blasting vibrations had not been contributing factors to the alleged damages at the residence or to the subsidence in the yard.”

The study emphasized “the need for mining companies to identify their permit areas in relation to nearby residential structures and to consider structure type for appropriate vibration limits and damage prevention.” Most important is for miners to keep accurate blasting records and “conduct monitoring with blasting seismographs to adequately evaluate and minimize tort claims.”

Prediction and Assessment of Overbreak

A study² from India published in February 2021 determined that, of those analyzed, stiffness ratio and stemming length are the most influential variables linked to overbreak.

The study was conducted at ASP Colliery, which is run by Bharat Coking Coal, a subsidiary of Coal India Ltd. The mine is located in East Jharia, in eastern India.

The seam there burns “due to spontaneous heating.” Blasting there is done comparatively quickly, and thus uses relatively less explosives. Because previous studies don’t, the authors sought to arrive at methods that would help predict overbreak at a fiery seam.

Previous studies on non-fiery seams found that the big factors driving overbreak were timing, confined gases, spacing, burden, stemming and stiffness ratio.

To determine the major factors driving overbreak at a fiery seam, the authors did 26 blasts and collected data on burden, spacing, stemming length, powder factor and stiffness ratio. That data was subjected to a statistical analysis and to an analysis by an artificial intelligence system to determine which could arrive at the most accurate prediction for overbreak.

For the 26 blasts, the bench height was roughly 6 meters (m) (19.7 ft), the drilling pattern was staggered, the number of holes per round was from 9 to 30, the number of rows per round was 2 or 3, hole diameter was 150 mm (6 in.). Electric detonators were used. The hole-to-hole delay was 25 ms. The row-to-row delay was 92 ms. The booster was 150 gm (5.3 oz) Emulsboost. The explosive type was site-mixed emulsion.

For the blasts, overbreak ranged from 1.4 m to 10 m (4.6 ft to 33 ft).

The data from the blasts was fed into two software systems.

One did a statistical analysis, an Multivariate Regression Analysis (MVRA) that determined the statistical relationships of variables to arrive at a formula for overbreak. The other was a Random Forest algorithm (RFA). It “creates the forest with several trees of the subsection of data and combination of all of trees will produce the output.” The output is the overbreak prediction.

WEKA software was used for the RFA.

The statistical analysis arrived at a formula the study concluded “will help in suitable blast design modification for minimizing the back break and optimizing explosive energy.” If BB is back break (m), B is burden (m), S is spacing (m), ST is stemming length (m), PF is powder factor (m³/kg), and K is stiffness, then BB = 28.47 – 6.04 x B + 4.28 x S +1.20 x ST – 7.31 x PF – 7.19 x K.

The formula gives a prediction of overbreak that proved to not be as accurate as that generated by the RFA. “The prediction of back break by RFA is close to the measured back break,” the study said. “Random Forest Algorithm technique can be used efficiently.”

Sensitivity analysis followed and found that “stiffness ratio and stemming length are most influential parameters.” The authors reported having no ties or connections to WEKA.

Presplit Blasting for Gas Drainage

A study³ conducted on the 1312 face of coal seam No. 3 in the Sanyuan coal mine in South China found that computer-optimized millisecond presplit blasting gave better gas drainage and significantly greater seam permeability than did conventional simultaneous presplit blasting or simple gas drainage through boreholes.

It reported that previous literature had proven that presplit blasting’s effects on seam permeability and gas drainage “can reduce or even eliminate hidden dangers,” but that same literature mostly fails to “consider the existence of gas in the coal seam” and, instead, is only on “the coal and rock mass as a solid medium.”

Gas drainage in the 1312 working face has historically been difficult. The study therefore sought to arrive at a process that would work for that seam.

The authors squared away a section of the seam roughly 400 m from the working face as a test area.

First the authors used ANSYS/LS-DYNA software to optimize hole spacing.

The software found that blasts from holes spaced at 5.5 m to 6 m created cracks that, as desired, ran the distance between the holes. At 5 m, the damage between the holes was too great. Beyond 6 m, “the stress wave” combination effect is weakened and the holes then aren’t connected by cracks. “Therefore, 5.5 m is selected as the best spacing to ensure the through-effect of cracks and save costs for the project,” the study said.

The test area was divided into three parts, each separated from the others by roughly 35 m. On one part, three blastholes were drilled 5.5 m apart, and would be blasted simultaneously. “The distance between the observation hole and the blasting hole was 2.25 m,” the study said.

On the second part, three holes, also spaced at 5.5 m, would be blasted with millisecond (ms) timing.

Previous field observations showed “the commonly used differential interval time is 15 to 75 ms, usually 25 to 30 ms,” the study said. The software then was used to create numerical models based on 0, 17, 25 and 42 ms.

The models showed that “delayed blasting cannot change the energy produced,” but the blasting can be “superimposed” by the delay, and “the action time” can “be prolonged to achieve the best blasting effect.”

Based on the numerical modelling results, the authors determined “when the interval of millisecond blasting is 25 ms, the development of coal and rock fissures is better, the effect of stress wave on medium is stronger, and the blasting effect is the best, which is helpful for gas drainage.” Therefore, “the time interval of millisecond blasting is set as 25 ms.”

The third part of the test area would be drilled, and the holes would be used for “natural gas drainage.”

The blasts were executed. The results from the three areas were compared.

The part with optimized millisecond blasting produced the best results by far. The “attenuation intensity of borehole gas emission was reduced by 67.65%,” the study said. The permeability of the seam was 30 times higher than that of the non-blasted area.

Comparing “conventional blasting and millisecond blasting, it can be concluded that the average gas concentration of drilling hole is increased by 1.47 times and 2.16 times by conventional blasting and millisecond blasting, respectively; the average gas purity is increased by 3.21 times and 4.73 times; and the average gas mixing amount is increased by 3.09 times and 4.27 times,” the study said.

The authors reported having no ties or links to the software company.

Dispute Resolution in Vietnam

Researchers in Vietnam tested a cloud- and accelerometer-based vibration-measurement system for use in, among other things, monitoring vibrations at or on properties near mines.

Vietnam has strict rules on blasting meant to prevent damages to nearby properties. Still, allegations emerge of property damage, and those allegations often result in costs for both the government and miners. “In Vietnam, there have been many conflicts between residents and government about the compensation policy for these damages,” the study⁴ said.

For example, a house near NuiBeo coal mine has levied complaints that vibrations from the blasts there have caused damage.

Prior solutions proposed in previous studies have included measuring the vibrations of a test blast with a concussion meter and then extrapolating from the data what future such blasts will do. Another solution considered is using various artificial intelligence systems to crunch data from previous blasts elsewhere and then model and predict the vibrations caused by future blasts.

Those solutions have their shortcomings, the study said. The authors “proposed an online monitoring system for vibration.”

The authors put together a system that uses an accelerometer to measure vibrations, a central station to collect the data from it, and a cloud-based platform featuring software to turn the data into useful information and for automatically generating reports and alert emails.

The authors did two test blasts, and placed the accelerometer next to a Blastmate III seismograph sensor, made by Instantel. The measurement point for one of the blasts was on the property that had previously made complaints. After the blasts, the authors compared the findings from the accelerometer and the seismograph to determine the closeness of both.

According to the authors, the accelerometer and Blastmate III arrived at near identical findings. The first blast was measured from 420 m away and had a maximum of total vibration vector (MTVV) of 3.214 mm/s. The second was measured from 515 m away and had a MTVV of 3.478 mm/s.

“All values are within the Vietnam standard limit,” the study said. For the size of the blastholes and blasts, the regulations “stipulates the minimum safe distance is 200 m; the MTVV is 25.4 mm/s.”

The cloud-based system would store the data from the blasts for use in fielding allegations of property damage due to vibrations from blasting. “The data that the system can record in real time, including amplitude and frequency, is stored in the cloud,” the study said. The data can be used to resolve complaints from residents near the mine.

¹ Kisi, Krishna (2021). Dispute Resolution in the Mining Industry: Lessons Learned from the Effects of Blasting on Nearby Structures. DOI: https://doi.org/ 10.1061/(ASCE)LA.1943-4170.0000487

² Sharma, Mukul (2021). Prediction and Assessment of Back Break by Multivariate Regression Analysis, and Random Forest Algorithm in Hot Strata/fiery Seam of Open-pit Coal Mine. DOI: https://doi.org/10.21203/rs.3.rs-267513/v1

³ Zhao, Dan (2021). Study on the Technology of Enhancing Permeability by Millisecond Blasting in Sanyuan Coal Mine, DOI: https://doi.org/ 10.1155/2021/8247382

⁴ Dao, Hieu (2021). Study on an Online Vibration Measurement System for Seismic Waves Caused by Blasting for Mining in Vietnam. DOI: https://doi.org/10.22044/jme.2021.10677.2028

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New Explosives System Offers Control, Optionality, and Ways to Improve Production

by jesse morton, technical writer

Orica reported the new 4D bulk explosives system delivers explosive energy tailored to geology and the desired blast outcome. “4D will enable our customers to access a wider range of energy-matched explosives in wet, dewatered and dry blastholes, delivering optimized explosive energy in real time,” said Adam Mooney, vice president, blasting technology, Orica.

The system is comprised of new bulk emulsion chemistry that enables a wider energy range, hardware upgrades to explosives delivery systems, or Mobile Manufacturing Units (MMUs), for improved loading accuracy, and the Orica LOADPlus control system for greater efficiency and productivity. It allows users to go beyond traditional thinking when planning and prepping blasts, Mooney said.

“Blasting has traditionally been considered in three dimensions: width, length and depth; however decisions on the application of explosives are often one dimensional in relation to the powder factor being applied to the blast, which typically does not account for differences in geology across the bench,” he said. “This essentially means that the same explosive blend and density of product are usually applied to each blasthole across a blast pattern.”

4D changes all that by offering more optionality, greater control and improved productivity. “4D combines emulsion blended with ammonium nitrate porous prills to support both pumped and augered loading methods across dry, wet and dewatered hole conditions,” Mooney said.

That ensures “greater on-bench productivity by Orica’s fleet of 4D MMUs without the need to change raw materials in the MMU,” he said. “Our customers can now apply a wider range of energy and respond to geology in real-time, regardless of hole condition to achieve their desired blast outcome.”

The long list of benefits include “the real-time tailoring of explosives energy to geology across a blast, delivering improvements in fragmentation and a more consistent muckpile, on-bench productivity and an overall reduction in drill and blast costs,” Mooney said.

On-bench productivity and efficiency is improved by reducing “the quantity of explosives loaded into wet holes, matched to geology, enabling more holes to be loaded per delivery,” he said. That saves “precious turnaround time and enables the loading of more blastholes per delivery.”

The ability to auger-load low-energy, water-resistant 4D explosives into dry holes provides sites with long sleep times insurance against adverse weather events, “giving our customers the peace of mind that blast performance will not be compromised,” he said.

The advanced bulk emulsion technology gives up to a “43% reduction in relative bulk strength for soft rock or technical applications, and up to 23% more energy for hard rock applications as compared to Orica’s current product ranges,” Mooney said. “Customers can better control blast vibration while adhering to their maximum instantaneous charge weight.”

Among other things, that means less “over-blasting in soft, wet ground, resulting in lower explosives consumption and overall blasting costs,” Mooney said. “The improved energy distribution and the potential for increase in bench heights enables customers to improve the productivity of drilling and blasting and mining near sensitive structures while meeting license requirements.”

By matching the energy to the geology and conditions, the user can reduce post-blast fumes. “With the capability to load lower-energy, water-resistant products into damp or wet blastholes, 4D reduces fume risk especially in softer geology,” Mooney said.

Multiple customers in Australia are trialing the system, “each with their own unique focus,” Mooney said. “For example, with one customer, we are demonstrating how 4D technology can reduce their overall drill-and-blast cost through lower explosives consumption, as well as better manage vibration in specific areas of their operation.”

Another customer is using it with Orica’s Clear range of bulk explosive products to demonstrate the reduction of fume risk in soft and wet ground. “We are also responding to interests in the North American market with our 4D technology set to enter the region by early 2022.”

New Orica MMUs will come standard ready for 4D. “4D is available on our Bulkmaster and Pumpmaster fleet of MMUs, which now include the Tread and Amerind supplied delivery systems,” Mooney said. “This enables seamless deployment of the technology to our customers globally.”

The system can be readily integrated with other Orica solutions for additional capabilities and benefits.

When paired with BlastIQ, a blast optimization platform, “the capabilities of both can be maximized to deliver the best blast outcomes far more efficiently,” Mooney said. “Customers can gain a much deeper understanding of the geology and blasthole conditions to maximize 4D capabilities and effectiveness.”

4D can be paired with SHOTPlus, Orica’s advanced blast design software, to enable designs “based on the required energy, irrespective of hole condition,” Mooney said.

“Blast designs developed in SHOTPlus can be wirelessly transferred via BlastIQ to the LOADPlus smart control system in the MMU to streamline the loading of blastholes according to blast design, thus eliminating the need for manual input,” he said. “As-loaded blast data can also be transferred to BlastIQ with the continuous logging of MMU process drives for product quality control and assurance.”

The advent of 4D “reinforces our commitment to technology innovation and is in line with our customer-centric technology roadmap and vision of transforming drill-and-blast operations to unlock greater mining value, and create safer and more productive blast outcomes for our customers,” Mooney said. “Our 4D capability demonstrates how our new technologies and solutions can be easily integrated to enable our customers to think differently, mine more efficiently and operate more precisely.”