Deep Excavation Impact Assessment in Urban Environments: Predictions versus Reality

To cater for the increasing population in Australia, we have had a property boom for several years. This has resulted in the demand for high-rise buildings with deep basement space. Within the Sydney metropolitan, these are preferably founded in rock strata. Invariably, proposed building developments are in close vicinity to other high-rise buildings, services and tunnels. In order to satisfy council’s Development Approval (DA) requirements for new developments, rigorous and sophisticated numerical analyses are commonly executed to assess potential induced deformation and its consequent damage risks. Predictions of such performances require a sound understanding of rock behaviour and their defects; these include the appreciation of locked in-situ stresses and relief mechanism, defect orientations, inclusions and presence of fault zones. This is better understood by creating geotechnical models based on appropriate geotechnical site investigations and interpretation by geotechnical professionals. During construction phase, specific monitoring plans are implemented whilst bulk excavation is progressed to verify the design assumptions. This is achieved by providing monitoring equipment including the installation of geophones, inclinometers, extensometers and survey targets. This paper attempts to provide an insight into the geotechnical project life cycle for deep excavations in an urban environment from design phase to construction support and implementation of monitoring measures.