River diversion for surface mining by Gábor Mérö, Trelleborg Building Systems

“The kolubara coal basin comprises an eastern and western part, divided by the Kolubara river,” explains 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 percent of the mine’s total productive surface, covers about 120 km2, but much of the area has long since been exhausted. However, the western part of the basin –spanning 480 km2 – at the opposite side of the river, remains unexploited. With its four open-cast pits and 26 million tonnes of annual production, the Kolubara mine (located some 40 kilometers southwest of Belgrade) supplies coal to several large thermal plants situated in the close vicinity, so finding a quick, reliable solution was vital to the local and national economy. “There is enough coal across the water to satisfy Serbia’s needs for decades to come,” enthuses Kovac. “But first, we have to get there!”

Hidrotehnika-Hidroenergetika issued a tender for a solution to the problem and against stiff international opposition, Trelleborg was chosen. “Rather than try to dig under the river, it was decided to divert it eastwards, into the already workedout areas,” explains Nebojša Miletic, managing director of Neshvyl Ltd., which represents Trelleborg in Serbia and Montenegro, Bosnia and Macedonia. “But because of the instability of the soil underneath we needed to line parts of the five-kilometer-long riverbed with a material that would ensure that the movement in the underlying soil would be absorbed”. The answer? Trelleborg’s EPDM rubber membrane. “The point is, rubber is elastic – it’s not just flexible,” points out Miletic. “It always reverts to its original form. Its characteristics are almost unaffected by water, cold, heat, stretching or whatever.”

Phase 1 of the project will be finished by the end of 2006 with further diversions planned over the coming few years. 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. “It will be a fantastic area for recreation,” says Hidrotehnika- Hidroenergetika’s Kovac smiling. “One thing that prompted us to choose Trelleborg is that it’s a global company – experts from Sweden and Budapest are flying in to supervise and advise; yet on the other hand, it has a local mindset that enables it to think of specifically local needs…like a boating lake!”

Need for speed

For the Kolubara managers planning their mine’s expansion, speed was essential – and only Trelleborg EPDM geomembrane system could meet that challenge. EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber whose balance of physical properties and chemical resistance make it ideal for a wide variety of rubber applications. The membranes are laminated with a thin layer of thermoplastic elastomer, a thermoplastic olefine that has many of the characteristics of vulcanized rubber, and then spliced using a new, patented splicing technique – Thermobond™ – whereby the seams are produced with a hot wedge in the form of two parallel welds with an air channel between them which enables the joins to be tested using compressed air. “We make something that is extremely robust yet adaptable, as well as resistant to heat, cold and moisture. Consequently, we were able to promise we would continue to install the membranes through the winter,” says Gábor Mérö, managing director of Trelleborg Industri Hungary, Trelleborg’s trading and logistics center in Central Europe, which is the source of the EPDM geomembrane solution to the Kolubara mine. “I don’t care if Serbia has its coldest, wettest winter ever this year. We’ll still get the job done!”

Solution: Trelleborg’s EPDM rubber membrane will be used to line parts of the new riverbed and stabilize the soil underneath.