Out & About
Working In the Salt Mines - Terex Trucks
Irish Salt Mining and Exploration’s Carrickfergus mine plays a vital part in keeping the UK’s road network open during winter.
Situated to the north of Belfast, Northern Ireland, Irish Salt Mining and Exploration’s (ISME) Carrickfergus mine was developed specifically to mine de-icing rock salt for winter road maintenance.
Founded in 1965, ISME is positioned in a prime location, thanks to its proximity to the coast, as well as the construction of a ship loading terminal, which enables the company to develop a successful export market.
The company’s 55-strong workforce currently produces between 300,000 to 500,000 tonnes of road salt per year, and provides local authorities across the UK with rock salt to help keep the road network open during the icy winter months.
Scottish local authorities are its biggest customer, followed by Ireland and then the rest of the UK.
Rock solid progress
Mining at Carrickfergus uses the ‘room and pillar’ dry mining method. There are five seams of salt, but ISME only mines one extensively, due to the thickness of the seams. (This is because 3.5m (12ft) of salt must be left above the excavated rooms as a support.)
At its deepest point, the mine reaches 305 m (1,000 ft) below ground.
The deeper you get, the larger the pillars, but on average the room sizes are 15.3 m (50 ft) wide and 9 m (30 ft) high. In the older part of the mine, they are just 6.7 m (22 ft) high, while the pillars are 39.6 m (130 ft) square in the newest part of the mine, and 27.4 m (90 ft) square in the older parts.
The geology of the area is fairly simple too. There are no gases or moisture to contend with, which makes mining a simpler process too.
During mining, the salt bed is undercut then drilled and blasted. Blasting happens at the end of each 10-hour shift, usually around 17.30, and sees three faces advance 3 m (10 ft) each time. The next morning’s first job is roof scaling, using a rotary cutting head designed specifically for the purpose.
The broken salt is then loaded into one of ISME’s seven Terex Trucks haulers, including two new TA400s, and hauled to the crushing plant.
Crushing and screening are completed underground before the finished product is transported, via a 2 km-long network of conveyors, to the surface.
The salt, ready for use, is then treated with an anti-caking additive and stored undercover for dispatch by sea from the company’s own quay, or by road.
Keeping to the mine’s speed limit is a key factor in reducing wear and tear, as well as minimizing fuel consumption. But the working conditions are still extreme, with the trucks having to cope with corrosive salt and dust, not to mention the temperatures inside the mine.