JSE-listed raiseboring and drilling services provider Master Drilling featured its horizontal raiseboring (HRB) technology and its advantages for mechanised mining at the latest South African National Committee on Tunnelling (SANCOT) breakfast, held in Woodmead last month.
Master Drilling mechanical engineer Willem Roothman, who presented the technology for mining and civil engineering applications, highlighted that there was a “big appetite” in the industry for mechanised mining, which formed the backdrop for the HRB technology.
“Master Drilling took conventional raiseboring and basically turned it to the side to create a method for excavating tunnels for underground mining applications and possibly also in civil applications.”
Among the key topics was the trial Master Drilling did at diamond mining group Petra Diamonds’ Cullinan mine, in Gauteng, with Roothman underscoring the applications, advantages and disadvantages of the HRB technology. Master Drilling was involved in the boring and excavation of a 180-m-long horizontal tunnel with a 4.5-m diameter through the diamond deposits.
Roothman explained that the construction method entails first drilling a smaller pilot hole through the kimberlite, which was challenging as no water could be used for flushing. The pilot hole also needed to be near perfectly straight. Subsequently, Master Drilling pioneered the use of vacuum air suction and laser-assisted directional steering, which aided the company to achieve an accuracy of holing within 20 mm of the required target.
Any raiseboring exercise requires access from both sides; for the Cullinan pilot project, Master Drilling decided to place the HRB machine on the north-end side of the mine and start reaming from the south-end side of the mine. “There was adequate ventilation and services, with enhanced storage capacity for all of the large components that we used . . .”
Although the same rig is usually used to do the piloting and the reaming in normal raiseboring, Master Drilling used a different rig than the actual raiseboring rig for the pilot drilling.
“Due to ground formation complications, we couldn’t use the same machine, so we opted to use a different machine that is normally used in the civil industry. The reason for this is that the kimberlite deteriorates drastically when in contact with water, thus normal pilot drilling equipment that uses water to flush the cut material from the hole could not be used. We therefore had to use the vacuum drilling system for safe and dry drilling purposes,” he explained.
“After we finished the pilot drilling, the pilot drilling machine was moved and the raiseboring machine was installed onto the same frame, which was designed to allow for the reaming machine to be mounted in the same position to keep the centre of the hole in-line with the centre of the machine, saving time with alignment and machine setup.”
In terms of removing cut material, Master Drilling had to find a solution to move the material from the face where it is cut to the back of the reamer. “We modified one of our standard reamers, adding scrapers, collection buckets and a muck-handling attachment. Initially, we used a vacuum system,” Roothman said.
However, because water was not used for dust suppression, the filters of the vacuum system clogged up, after which Master Drilling then used a load-haul-dump machine to collect the muck more efficiently.
There were zero injuries during the trial, which is something that mines are “very interested in and it’s one of the advantages of mechanised mining, compared with conventional methods”, Roothman said.
The HRB technology has many other benefits, including improved safety and advance rates, as well as improved structural integrity of the tunnel itself. Master Drilling CEO Danie Pretorius said the technology holds great potential to increase mining productivity, owing to its continuous process of rock boring.
The advance rate of the HRB technology had almost doubled, compared with conventional methods. The costs are also in line with the costs of conventional methods. Further, the technology can be used in other disciplines, such as civil engineering and energy.
However, the advance rate depends on the type of geology. “One of the biggest drawbacks is that you need to have access on both sides and you can only drill straight tunnels – you have to have a straight line of sight,” Roothman acknowledged.
Following the trial at the diamond mine, Master Drilling completed several proposals and submitted bids for tenders to various mining companies.
SANCOT Breakfast Talks
The Master Drilling breakfast talk took place on February 15 at South African multidisciplinary engineering firm GIBB’s offices in Woodmead, Johannesburg. The breakfast was also sponsored by GIBB.
SANCOT has been hosting breakfast talks every two months since last year. Three talks have been hosted to date, all at the GIBB offices.
The first talk, Tunnelling Trends in South Africa, considered the history of tunnelling in the country and was presented by SANCOT chairperson and GIBB senior associate Ron Tluczek.
The second talk, presented by GIBB associate Monique Wainstein, highlighted the potential of using microtunnel boring machines to augment the water supply for Mthatha from the Mthatha dam, in the Eastern Cape.
“The SANCOT Breakfast Talks aim to promote interaction and closer communication among personnel and companies in the mining and civil industries,” Tluczek said, adding that it provided a platform where expertise and experience gained in civil and mining underground excavation could be shared, he concluded.