The fine art of precision drilling

On a mountain top, high above the Black Hills of South Dakota in the United States, work continues on the Crazy Horse Memorial – the largest and perhaps, most amazing, monument ever attempted.

This effort to sculpt a mountain into an enduring tribute to a towering figure in American history has been going on since 1948. No-one seems to be able to predict when this massive and difficult project will be finished. However, a dedicated crew of talented workers attacks the 172-metre mountain each day, and slowly, the great sculpture emerges against the wide-open South Dakota sky.

The drillers and blasters on the mountain are not deterred by winter storms or summer heat – or the millions of tonnes of rock that remain – until the sculpture of Chief Crazy Horse is finished. Along with the rest of the Crazy Horse Memorial’s staff, they seem imbued with the spirit of their mission.

A huge impact
Even if the spirit is willing, the flesh needs a lot of help. Throughout the years, numerous manufacturers and distributors have aided the Crazy Horse project, by providing much-needed drilling and construction equipment. The latest piece ? and only the second brand-new item to come to the mountain ? is a Commando 300 R surface drill from Sandvik Mining and Construction. The drill is part of Sandvik’s Tamrock line.

The drill at work
With efforts now focused on removing excess rock from the horse’s head, the drill is working along the area that will become the horse’s mane. Since 19 January 2006, a total of 13,600 tonnes of rock have been blasted and removed from the mountain. The drill has been responsible for about 2700 of those tonnes, according to Sandvik. Millions of tonnes of rock have been removed throughout the decades – including 180,000 in the last six years – and another 450,000 tonnes will be removed to get workers within six metres of the final proportions of the horse’s head. At that point, large-scale blasting will cease and finishing work will begin.

The Crazy Horse Memorial is a monumental sculpture of Chief Crazy Horse on top of South Dakota’s Thunderhead Mountain. When completed, the mountain will have been transformed into a 360-degree sculpture of Crazy Horse, astride a horse and pointing out across the Black Hills. The mountain is 172 metres high, and nearly 2000 metres above sea level.

The chief’s face, completed in 1998, is 27 metres high. The chief’s arms will reach 69 metres. The horse’s head – on which work is now concentrated – will be 67 metres high, with 14-metre-long ears, and eyes that measure five metres by four metres.

For comparison, each of the four heads on nearby Mount Rushmore is 18 metres high, and the completed Crazy Horse Memorial will be 2.5 metres taller than the Washington Monument.

Precise sculpture measurements
Begun in 1947 by Boston-born sculptor Korczak Ziolkowski, the memorial has been under constant construction since then. Korczak, as those on the project still affectionately call him, worked from a 1:34-scale model that is still at the site. The current engineers and drillers/blasters follow scale models of the monument, using both computer-aided design and manual measurements to transfer dimensions from the models to the mountain. The chief’s head, for example, required 10,000 measurements to ensure it precisely followed the model. Constant surveying of the sculpture from the mountain’s base helps to keep the mountain crew on target.

The memorial draws 1.3 million visitors a year. Two-to-three times a week, they are treated to the spectacle of watching a blast on the mountain, about 1.6 kilometres from the visitors’ centre. When a blast is imminent, visitors are alerted, giving them a rare opportunity to see the handiwork of an experienced drilling and blasting crew.

Terrain demands safety and precision
The drill is equipped with a HL 300 hydraulic top hammer rock drill, with a maximum recommended diameter of 63.5mm and a maximum practical depth of 15 metres.

Typical applications for the drill are foundation drilling, road cutting, and trenching. It has a four-wheel oscillated drive carrier for rough terrain capabilities, and can be easily transported between job sites on a truck or trailer. In the case of future work on the upper areas of the Crazy Horse monument, it may also be moved and put in place with a crane, according to the project’s engineer Kevin Hachmeister.

The drilling and blasting on a project, such as the Crazy Horse Memorial, requires extreme precision and care. According to Sandvik, its drill works well for removing excess rock as well as for fine finishing work on the horse’s head.

“With the Commando’s small size, we can use the crane to put it in place and work on narrow benches,” Mr Hachmeister says. “At that point, it will replace hand drilling, something we did for 10 years in carving Crazy Horse’s face.”

Jeff Hermanson, a member of the mountain crew, says the surface drill gives him and others the ability to manoeuvre safely on the narrow benches alongside the mountain, many metres above the ground.

Additionally, its remote control feature enables an operator to activate the unit once it is in place and set up for drilling. In the case of the Crazy Horse mountain crew, the operator can find a safe place to stand and oversee the operation, even when the unit is on a narrow bench and close to the edge of the mountain.

Getting to those benches also requires an agile and manoeuvrable drill because many of the access roads that the crew builds alongside the sheer rock walls are fairly steep.

Blasting on a massive scale
The unit drills 47.625mm diameter holes, using 31.75mm drill steel. In comparison, many small quarries and construction projects may use 38mm drill steel, with 50-75mm diameter holes. However, Mr Hachmeister indicated that keeping the holes smaller on Crazy Horse was the key to precision blasting.

“Unlike a quarry, we don’t care so much about the rock that is blasted away,” Mr Hachmeister said. “We care about the quality of rock that’s left behind. We need to leave relatively smooth rock walls behind the blast area so we can control the progress of the sculpture.”

The standard blast pattern on the mountain includes six metre vertical holes and patterns of horizontal holes that reach 2.5 metres. The unit can drill vertical and also horizontal holes. Detonating cord and water gel explosive are used, employing the least amount of explosive energy to split the rock from the mountain. It is a task the mountain crew has repeated hundreds of times throughout the years – with spectacular results that are clearly visible to the visitors on the ground.

Mr Hachmeister compares it to a sculptor who is painstakingly removing layers of rock to find the sculpture underneath. In this case, however, the sculptors are working with equipment, such as a surface drill, instead of a hammer and chisel.

The nine-member mountain crew includes four certified drillers and blasters, though many were rock climbers before they came to work at the memorial. All have been on the mountain for at least 12 years. They are led by foreman Casimir ‘Cas’ Ziolkowski, son of the late sculptor, who has worked on the memorial for 40 years.

Seven of Korczak and Ruth Ziolkowski’s children are involved with their father’s project, as well as several grandchildren. Ruth Ziolkowski still lives on-site and oversees the project, creating a strong link to the past.

Many members of the mountain crew have spent years on the project and they form another link – between the present and the future. Crewmember Duane Straw put it this way, “We all take pride in our work. We know this work is a part of history. When we tell people what we do, we always get a positive reaction.”

Source: Sandvik Mining and Construction

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