OasisLMS

Abstract: The Lower Plenty Road Interchange for the North East Link project in Melbourne requires the use of a specialist foundation technique known as a diaphragm wall. The diaphragm wall was selected as a robust and economical solution that is structurally stable and watertight and allows for the cut and cover tunnel excavation method to be undertaken once the diaphragm walls are installed. The specialist ground engineering contractor Trevi Australia Wagstaff Piling Joint Venture (TAWP JV) has mobilised four Hydromill cutters to the project which is the first instance of its kind in Australian history. These cutters install diaphragm walls up to 45m in depth in individual interlocking panels up to 6.7m long and 1.2m in width using a bentonite slurry as support fluid. There are 471 of these individual diaphragm wall elements referred to as ‘ panels’ on this project spread over 900 lineal metres which encompasses significantly varying and challenging ground strata. One such significant challenge has been the presence of major geotechnical fault lines characterised with steeply dipping bedding planes with a relatively high strike to the diaphragm wall trench. These sharply dipping bedding planes have interacted with other joints and defects within the rock mass which has led to block wedge failure of the wall and collapse of the trench. Post collapse remedial works and the use of preventative design and construction measures including reducing panel geometry, adjustments to bentonite mix properties and performance, soil nailing, pressure grouting and increasing the pressure head differential between natural ground water and the bentonite support fluid were implemented by the project. Other geotechnical challenges on this project also include extremely high strength rock layers and the presence of organics which can adversely affect the bentonite support fluid characteristics.

Mr. THADU KHIN

Annual Conference Proceedings