llector, the 3.2-km-long Breitenleer Sewer, in the city’s north-east.
Today, 99 percent of Viennese households are already connected to the public sewer system (an absolute peak by international standards), and the new project adds another 800 households. The new sewer, with an inner tunnel diameter of 1.8 m, is constructed at a depth of 2 – 6.5 m largely by using the microtunneling technique.
Peter Ruso, head of Municipal Department 30 (Vienna Sewers) and in charge of project coordination, describes the method: “The type of machine in use is a so-called earth pressure balance machine; as the cutter head forges its way through the ground, the loosened soil and rock is mixed with water into a muddy mass which is then extracted through a discharge line. At the same time, the resulting void is lined with sewer pipes made of reinforced steel, which are introduced into the launch shaft one by one and pushed ahead hydraulically.”
Technical aspects were only part of the reason for choosing this no-dig technique; what also tipped the scales was that only few excavations alongside a separate construction lane are required and that the burden of building operations on neighbourhood residents and local traffic can be kept to a minimum.
Ulli Sima, Vienna City Councillor for the Environment, is also delighted that after project completion in spring 2009 the new Breitenleer Sewer will serve a double purpose: it brings Vienna‘s sewer network one step closer to completion and the post-construction area (the construction lane) will be converted into a cycle track so that Vienna’s outermost city limits can then also be reached by bike.
(Source: aqua press Int. 1/2007)