Mercedes Zetros 600 metres underground

When you need to drop a massive great big truck 600 metres underground through a 2.9 x 2.5-metre mine shaft, there are a number of logistical challenges. Chief of which is that massive great big trucks do not fit in 2.9 x 2.5-metre holes.

This was the very melon-scratcher German salt-mining company Esco faced late last year when it needed to install a 7.8 x 2.5-metre Mercedes-Benz Zetros water transporter 0.6 kilometres underground.

"We searched for an off-the-shelf vehicle to reduce costs," says Volker Grzeschuchna, head of mechanical and electrical engineering underground at Esco. "But the vehicle had to feature a robust chassis, all-wheel drive and a fully automatic transmission to cope with the difficult driving surfaces.

"A payload of at least seven tonnes was necessary: a six-tonne tank capacity and an additional tonne to account for the bodywork. The 326bhp Mercedes-Benz Zetros was a good choice."

Good, but by no means perfect. For it to join the 146 other specialty mining vehicles through said shaft, it had to be... cut in half. Then lowered 380 metres on a hook. Then welded back together. Then strengthened with a batten. Then mounted with a 6,000-litre stainless steel water tank. Then driven. 600 metres beneath your feet.

Why you'd go to this sort of trouble does suggest that having a water truck down a mine is Quite an Important Thing. And it is. Humidity in the Bernburg salt mine is quite low - only 25 to 30 per cent. So when tractor shovels regularly drive blasted lumps of salt to crushers, which gets ground and sieved, the going tends to get dusty.

Which is where the Benz comes in. With a specially adapted Allison transmission, it waters the road at approximately 6mph with its rear spray bar, covering about 250 miles a month. It also refills water containers within the 4.6 x 2.1-mile mining area, so workers and machines can rinse off the salt dust.

It all sounds like dismally slow progress, but salt soil is hard and rough, and the narrow-galleried and pitch-black tunnels it works itself through include gradients of up to 20 per cent. Just to be let loose here requires special training.

So, will it ever see the light of day again? Er, no. "At least, not in one piece," says Grzeschuchna. "In 30 years at the earliest, it will be disassembled into individual parts and transported for scrapping."