Japanese limestone quarry achieving safe, vibration-free mineral extraction with Wirtgen surface miners
LIMESTONE has been extracted from Ube Isa Quarry in Yamaguchi, Japan, since 1948. What makes this site special, however, is that it is located in the immediate vicinity of a residential area – with the nearest home only 150m away.
In 2012, quarry owners Ube Industries hired Okumura Engineering Corp. to mine the limestone in an environmentally friendly way that would not affect the surrounding area. To achieve this, Okumura made the decision to use a Wirtgen surface miner.
Tomoyuki Shodai, general manager of the mining department at Ube Industries, said: ‘The densely populated area around the quarry is a challenge, because environmental effects such as vibration and noise for local residents limit the size of the work zone.’
It is due to the close proximity of local residents that conventional blasting methods are no longer an option at the site. As a result, Ube Industries had faced the prospect of never being able to fully exploit the deposit, which would have meant a loss of several million tonnes of limestone for the company.
However, surface mining allows extraction of the mineral without the use of explosives. By cutting into the ground to remove the materials, this method simplifies the complex extraction and preparation process, with mining, crushing and deposition of the material in windrows all carried out in a single operation.
In addition to the Wirtgen 2500 SM surface miner that Okumura have been using at Ube Isa Quarry since 2012, last year the service provider added a second machine – a Wirtgen 2500 SM Vario (pictured).
These two machines allow Okumura to create extremely stable and steep mining walls with narrow benches, thus safely expanding the mining area for Ube Industries. As a result, the limestone deposit is now being fully exploited.
‘Using Wirtgen surface miners allows us to mine the southern side of the site, which would have been impossible with the blasting method,’ commented Mr Shodai.
Another advantage of surface mining is the central-drum concept. The cylindrical cutting drum is located close to the machine’s center of gravity, resulting in maximum cutting performance and exact cutting depths in hard rock. The result is a uniform material and a flat surface, which, owing to its stability, can easily be driven on by construction site vehicles.
In addition, surface miners are very environmentally friendly compared with conventional drilling and blasting methods. Vibration-free extraction without drilling and blasting significantly reduces the amount of dust and noise produced.
The 2500 SM Vario used at Ube Isa Quarry was specially modified for the customer to meet these requirements. The sealed cutting drum housing as well as the specially equipped sound attenuation and dust-separation filter further reduce dust and noise in the immediate vicinity of the residential area.
In 2017, the 2500 SM, which is equipped with a 2.5m cutting drum, was used on 210 days and was able to extract almost 60,000 tonnes of limestone over an area of 4,000 square metres. By adding the 2500 SM Vario, the company was able to extract a total of 32,000 cubic metres of limestone in 2018 – a significant increase from the 22,000 cubic metres extracted in 2017.
The 2500 SM Vario is particularly suitable for hard rock, as is the case at Ube Isa Quarry. Thanks to the central-drum concept, the drum is located very close to the center of gravity of the 135-tonne machine, which allows it to penetrate into harder layers.
The Vario miner gets its name from its variable control system, which allows the drum’s torque to be adapted to the properties of the rock, preventing excessive wear on the bits and extending their service life.
In addition, the Vario miner can be operated at different milling drum speeds, which makes it highly versatile when used in variable external conditions. The machine’s direct drive makes it particularly efficient, whilst the turbo coupling mounted before the drive unit dampens vibrations, is extremely wear-resistant and requires little maintenance.
The 2500 SM Vario was also optimized for the quarry in terms of operator safety. Instead of controlling the miner from the cab, the operator can operate the machine via remote control. This is particularly advantageous on steep slopes, as the machine operator is not only in a safer location but also has an even better view of the area being mined.
Okumura originally used standard picks with a shank diameter of 38mm for their surface mining operations at Ube Isa Quarry. However, owing to the hardness of the limestone, which has a compressive strength of 40–80MPa, the picks suffered so much wear that the company decided to use picks with a larger-diameter shank.
Picks with a shank diameter of 42mm, in combination with the HT15 tool-holder system, have proven perfect for the application and maximize pick utilization. The pick holder’s exchangeable base also significantly reduces the changeover time and increases the availability of the machine for limestone extraction operations.