Deep Cut-Off Walls constructed under Dams with Trench Cutters

Up to now, the BAUER Trench Cutter Cut-Off Wall (COW) technology has been developed for more than 20 years for use on large dams. The special task of a COW is to mitigate seepage and therefore COW's are utilized either on dam rehabilitation projects or on new dams as well. Seepage mitigation, for the long-term stability and the safety of dykes and dams, is a major issue to the designers. Cut-off walls constructed using Trench Cutters nowadays can be installed to depths in excess of 120 m / 400 ft and into bedrock with strengths well above 160 MPa / 23,000 psi. In the near future the job definition by client-side will ask for depths over 200 and 250 m and very hard rock. Modifying Trench Cutters in the way to react on this definition and developing the right construction methods are the main challenges for the future. Above all, the measuring technique must be modified to ensure the quality of the diaphragm wall. Concerning the permeability of the total wall the quality of cold joints is the most important factor, for which cleaning before concreting could be mandatory. Specific tasks will be discussed through various COW projects recently executed by BAUER Spezialtiefbau GmbH.