The Arocs underground at Wacker Chemie AG.


The Arocs underground at Wacker Chemie AG.
Photos: Henrik Morlock

150 metres below the Earth’s surface.

Salt from the mine in Haigerloch-Stetten doesn’t just keep our roads free of ice in winter, it also keeps Wacker Chemie busy. The Arocs 4142 8×4 ensures that the cavities left behind by mining the salt remain safe for a long time to come. In the salt mine run by Wacker Chemie in Haigerloch-Stetten, the robust construction-site specialist takes on this daily challenge with ease.

Stefan Stehle uses a remote-controlled drilling vehicle to makes holes in the salt dome ready for the explosive charges.

Its playground is deep underground: a huge salt dome with a network of tight roadways and dark shafts which have seen more than 160 years of history.

Michael Schulz is an electrical engineer and General Operations Manager.

Mining expert.

“All the rock salt below here was once dissolved in sea water”, explains Michael Schulz, General Operations Manager at the mine. “The shell limestone salt deposits formed around 230 million years ago when water in prehistoric sea beds slowly evaporated and left one layer of salt after the other. At the time, the first dinosaurs had just developed on the supercontinent Pangaea”. The first wave of evaporation only lasted around 100 years. The resultant deposits are today around 100 to 160 metres below the ground and are up to 15 metres thick.

160 kilometres of roadways below the Earth's surface.

King Frederick William IV of Prussia was the driving force behind the underground treasure hunt near Haigerloch in 1852. The year 1857 saw rock salt being extracted for the first time in Stetten. It was initially used in cooking and as salt lick for cattle. In 1960, Wacker Chemie bought the salt mine. “Salt has been mined in Stetten using the room and pillar technique for a very long time”, explains Michael Schulz. To achieve this, long roads initially had to be constructed inside the mine.

The Arocs 4142 8×4 handles the underground salt roads with ease.

Schulz says: “Our road network in the mine is around 160 kilometres long. The whole area makes up twelve square kilometres and is thus about the same size as Lower Manhattan”.

Rock salt extraction.

In Germany, only around three percent of the salt mined is used by the food industry. The biggest consumer of salt in Germany is the chemical industry, which converts around 75 percent of the extracted rock salt into valuable products. Some 80 percent of all pharmaceutical products come into contact with salt or its secondary products as part of their manufacturing process. Be it silicone sealant from the DIY store, pure silicon in photovoltaic systems or polymers for facades and wood preservation – salt from Stetten isn’t just an everyday occurrence on gritted roads in winter.

Wheel loaders feed the roller crushers with crude salt.
Frank Stocker drives a Mercedes-Benz Arocs 4142.

A miner’s best friend.

Frank Stocker’s workplace is anything but ordinary. At the Stetten salt mine, the 36-year-old drives an Arocs 4142 8×4 with a Fliegl walking floor tipper. It’s with this vehicle that he fills in the cavities left by the salt mining operations. “Everywhere where salt is removed, we backfill to ensure sustainable mining”, explains Stocker. “Backfilling products are essentially mineral waste from the industry. We fill the rooms back in in order to secure them”. To complete the backfilling, around 50 trucks are in daily operation, driving along the Clara tunnel directly into the pit.

Transfer station backfill bunker.

As the backfill cavities have a maximum headroom of between four and six metres, regular road-bound trucks with a tipper body cannot directly unload there. Instead, they drive to a backfill bunker directly at the entrance to the pit, where there is sufficient headroom for the trucks. 

In the backfill bunker, an excavator loads the Arocs.

“Here, the road-going trucks can tip out their load and a digger can then load it onto the Arocs. I then drive around 20 tonnes of backfill material per journey through the salt dome and into the rooms which need to be filled”, says Stocker.

Watch the Video at RoadStars.