Stabilisation of the Zelazny Most copper mine tailings dam in Poland could be achieved using new diaphragm wall technology developed by Soilmec, according to yesterday’s 53rd Rankine Lecturer.
Use of new hydromills capable of creating 250m deep diaphragm walls to build stabilising shafts was presented as a possible solution to ground movements in parts of the dam in the lecture delivered by Politecnico di Torino professor Michele Jamiolkowski.
The 14km long ring dam impounds tailings from three copper mines in south west Poland and the operation contributes around 1.5% to the country’s GDP. However, current rates of deposition mean that the dam height on the eastern side, which is currently 62m high, could trigger failure in 2016.
The dams, formed using an upstream method, have been the subject of a 20 year investigation to review their stability which has revealed that glacial activity has resulted in a complex geological model with shear planes in the Pliocene clay at depth where the strength is close to residual levels.
Installation of a toe weight berm on the starter dam, construction of relief wells and movement of the dam crest between 2007 and 2009 has helped to slow the deformation but Jamiolkowski’s team has predicted that this is not enough to prevent failure as the dam in raised.
Jamiolkowski said that construction of a 120m deep, 20m diameter shaft to intercept the shear planes would sufficiently change the kinematics of the deformation to allow the mines to continue operating without immediate risk of dam failure. He said that current shaft boring equipment could not bore the diameter or depth of shaft required to achieve the effect but he hoped that Soilmec’s new hydromills could be make it a viable option.
At the end of the event the British Geotechnical Association announced that Oxford University professor of civil engineering Guy Houlsby will be the 54th Rankine Lecturer and is scheduled to deliver his lecture in March 2014.