This paper details the design of a multilevel anchored diaphragm wall which forms part of a cut and cover tunnel for the Eastern Distributor Motorway in Sydney. The paper also presents settlement predictions and proposed monitoring program for the structure, as well as settlement criteria of adjacent heritage structures and a comparison of predicted and monitored settlements. The case study showed that the settlement control is achievable with careful planning, design and a monitoring program.
The Eastern Distributor Motorway comprises a driven tunnel beneath Sydney's eastern CDB and the excavation of cuttings in soil and rock strata adjacent to existing buildings. The northern approach to the main driven tunnel at William Street is a cut-and-cover tunnel formed by a multi-level anchored diaphragm wall system, with retained cutting depths between 6 metres and 13 metres. A portion of the eastern-side wall is adjacent to Kidman Terrace which is a heritage building structure and only 0.5m from the proposed diaphragm wall, and a further building 136 Cathedral Street. For these buildings careful design of the retaining structures to deep excavations was required in order to control the total and differential settlements expected due to excavations. To achieve the design criteria specified by the Department of Urban Affairs and Planning (DUAP), a multi-level prestressed anchor wall was designed. Lateral wall displacements and ground settlements were predicted at the design stage and a report was released to the public for comment. Leakage of ground water through both the joints between diaphragm wall panels and underneath the toe of wall was one of the major concerns. Lowering of ground water table could result in additional settlements to those predicted due to excavations. Serviceability state movements of the wall were analysed using both an empirical approach and a numerical analysis.