Over the past three years, there has been a significant increase in the use of three-dimensional (3D) photogrammetric, or stereophotogrammetric, blasting survey and profiling technology for both surface and underground mining applications throughout the US, Canada and Europe, says international blast engineering and consulting firm RA McClure (Ram).

Meanwhile, South Africa is also starting to expand the use of this technology in its mining and construction sectors and explosives industries, says Ram president Robert McClure.

Photogrammetry is the science of taking measurements from images, while more modern stereophotogrammetry involves the measurement of 3D information from two images showing the same object or surface from different angles.

The technology can be applied in both surface and underground operations to characterise rock mass, design bench blast patterns and provide drilling information and minimum burden reports for optimised blasting.

The minimum burden of a borehole refers to a 360º spherical view of the shortest distance from the designed borehole location to the free face.

McClure, who earlier this month spoke at BME’s nineteenth annual explosives conference, says industries that use explosives are challenged to find the right equipment and experienced personnel to profile, survey, design and lay out blast patterns to meet today’s demanding performance and environmental needs.

“Companies often use a variety of profiling and survey technologies that are selected for their simplicity and do not meet the performance level needed to ensure blast safety or performance,” he points out.

Meanwhile, complexities of other technolo- gies require significant training and make it difficult for the occasional user to maintain proficiency.

These challenges have left the industry seeking improved technologies that deliver the performance level needed, while offering user-friendly software that requires minimal training.

McClure says, as a result, industry role-players are recognising the benefits and the superior performance of 3D photogram- metric survey and profiling technology.

“Advancements in this technology are providing the industry with a more accurate and efficient approach to profiling and surveying, while significantly improving safety and performance.

“As a result of the technology’s various benefits, the industry is looking to standardise its equipment and training needs to manage its surveying and profiling programmes more effectively,” McClure notes.

The system uses images taken from a single- lens reflex digital camera that has been calibrated by its developer, 3G imaging solutions provider 3G Software & Measurement’s engineering facility, prior to purchase.

He explains that these images are reconstructed and scaled to create an accurate 3D image, which provides a perspective that enables the operator to better determine the geological characteristics on the face of a highwall mining site.

This was not possible with reflectorless laser systems that were the previous predominant survey tool, says McClure.

“The stereophotogrammic system uses the camera’s pixels as points of reference, capturing significantly more reference points on the pit or mine face than laser systems. This makes stereophotogrammetry a more accurate system.”

Further, the blast can be georeferenced to local or global coordinates by using the system’s advanced blast design software to survey the targets and enter their coordinates. This geotechnical information is used to improve safety, mine planning, wall control and information for fragmentation modelling.

The initial ‘as-designed pattern’ is generated in the software with the proposed borehole locations, angles and azimuth. When drilling problems occur and borehole parameters change, the design can be updated to generate an ‘as-drilled pattern’ that reflects the changes.

Borehole survey data can then be integrated into the updated ‘as-drilled pattern’, providing detailed graphics that depict the true minimum burden of each borehole.

In underground operations, the detailed 3D images can be used to improve shot design and characterise geological features that could potentially cause poor performance. The detailed images provide the location, length, width and other features necessary to change the design or explosive loading to be identified.

McClure says underground blast quantification and benchmarking have always presented a challenge, owing to the extreme conditions of the mining environment. However, 3D photogrammetric technology eases the survey process.

Underground images are collected in the same manner as surface operations, except the camera is positioned on a tripod.

The underground 3D images are used to profile and measure over and under breakage at the mine face, roof and sidewalls. Uneven and concave mine faces can be quickly surveyed so that corrective action can be taken to determine drill depths.

“The flexibility, accuracy and multipurpose use of the system provides a significant cost advantage,” he notes.

Training

McClure says Ram provides specialised classroom and field application training on the system at the end-user’s location.

However, he points out that end-users do not require an extensive surveying or engineering background, as the system is user-friendly.

“The fact that the system uses a camera to collect the survey data makes it easy to use – the operator only has to take pictures.

“We find that personalised training is the most effective way for individuals to quickly learn how to operate the system and the software. This helps the user integrate the system into the company’s blasting or geotechnical program with our assistance,” McClure says.
Further, he adds that companies that use the 3D photogrammetric technology will often want additional systems or will upgrade their existing systems for improved capability. In these cases, Ram provides custom-tailored training.

McClure expects that the use of stereo- photogrammetric technology will expand exponentially, locally and internationally when the mining industry becomes more aware of the advantages it offers.

“This technology provides the industry with a versatile tool, it meets or exceeds the industry’s needs and provides a way to standardise equipment and training. The performance of this technology and ongoing development will continue to stimulate the demand for greater accuracy and performance,” he concludes.

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