Melbourne Main Sewer Project – Construction Phase –Soft Ground Tunnelling in the Yarra Delta

摘要

This paper discusses the challenges, solutions and lessons learnt as tunnelling work continues on thernMelbourne Main Sewer Replacement (MMSR) project.rnThe MMSR project is a $220 million dollar project for the Melbourne Water Corporation. It involvesrnthe construction of approximately 4.2 km of new sewer from the southern fringe of the CBD throughrnthe inner metropolitan suburbs of Port Melbourne and South Melbourne.rnOf the 4.2 km of sewer currently in construction approximately 2.2 km will be constructed usingrna 2.95 m diameter Lovat EPB tunnel boring machine (TBM) with approximately 1.9 km of smallrndiameter (300 to 600 mm) reticulation sewers constructed using trenchless techniques.rnThese sewers are being constructed in a dense urban environment, which means that the tunnelsrnand shafts are often in close proximity to buildings and structures. The underground constructionrnof the sewer is further complicated by the variable geology of the ancient Yarra River delta whichrnincludes weathered basalts, the infamous Coode island silt formation and fi ne loose sands.rnSome of the key challenges and lessons learnt so far during construction include:rn? steering and alignment control of the TBM through very soft silt with little residual strength,rn? development and refi nement of a monitoring and alarm system for leaving the machine dormantrnon a day works only project,rn? control and measurement of tunnel lining defl ection during ring build and grouting,rn? prediction and monitoring of surface settlements during tunnel excavation,rn? improved understanding of the geology and hydrogeology at this previously unchartered area ofrnMelbourne,rn? consolidation settlement due to dewatering at shafts required careful construction controls, andrn? ground support and excavation in close proximity to the existing 110 year old sewer which requiredrnvery detailed risk control measures.