“The Kolubara coal basin comprises an eastern and western part, divided by the Kolubara river,” said Ivan Kovac, marketing manager of Hidrotehnika-Hidroenergetika, the Serbian civil engineering construction company in charge of the expansion project.

The eastern part of the basin, which represents 20% of the mine’s total productive surface, covers about 120 square kilometres and produces 26 million tonnes of coal annually, but much of the coal reserves have been exhausted.

However, the western part of the basin on the opposite side of the river, spanning 480sq.km, remains unexploited.

Hidrotehnika-Hidroenergetika issued a tender for a solution to expanding the mine’s operations and chose global industrial group, Trelleborg for the job. Trelleborg is a leader in advanced polymer technology and develops solutions that damp, seal and protect in demanding industrial environments.

In consultation with mine managers, Trelleborg decided that to expand the coal mine, the company would need to divert the course of the river for 5km.

“Rather than try to dig under the river, it was decided to divert it eastwards, into the already worked-out areas,” a Trelleborg spokesperson said.

“But because of the instability of the soil underneath, we needed to line parts of the 5km-long riverbed with a material that would ensure that the movement in the underlying soil would be absorbed.”

Trelleborg’s EPDM (Ethylene Propylene Diene Monomer) rubber membrane was used to line parts of the new riverbed and stabilise the soil underneath.

“The point is, rubber is elastic – it’s not just flexible,” the spokesperson said.

“It always reverts to its original form. Its characteristics are almost unaffected by water, cold, heat, stretching or whatever.”

The river’s new course will take it through an enormous pit, which was originally dug to store ash from one of the nearby power plants but will now serve as a recreational lake for local residents.

Kolubara mine managers said Phase 1 of the project is due to be finished by the end of this year, with further diversions planned over the coming few years.