Project Residual Category Potential event phase risk rating Construction Damage to rail lines Construction 2 Western Medium – stage excavations resulting in portal cause ground disruption of 1 Tunnels – movement services (western portal to Arden station) Construction Damage to tram Construction 6 CBD South Medium – stage excavations lines resulting in station cause ground disruption to movement services Construction Damage to Telstra Construction 6 CBD South Medium – stage excavations Tunnels resulting in station cause ground disruption to key movement infrastructure Tunnel May necessitate a Construction 1 Tunnels Medium – construction change in (western portal encountering rock construction to Arden with greater rock methods in a zone station, Arden mass strength of geological station to than expected conditions leading to Parkville increased ground station, CBD movement or cause South station TBM to go off-line. to Domain Requirement to station) change construction 2 Western – method or portal repair/retool TBM 3 Arden – could result in station project delays Ground heave as Unacceptable Construction 1 Tunnels Medium – a result of ground movement (All) excessive face 2 Western – pressure by the portal TBMs in shallow cover areas The assessment has been based upon a review of the ground conditions and preliminary modelling that provides a conservative estimate of the potential settlement values, their distribution and their effects on structures and civil infrastructure. The risk register was developed with the geotechnical risks associated with geological variability in mind and the potential for excavations to encounter unforeseen/unexpected conditions. The levels of confidence in the current interpreted geological model are reflected in the current register. Ongoing geotechnical and hydrogeological investigations would allow refinement of the model and increase levels of confidence in those areas identified as having medium residual risk ratings, potentially reducing them to low.
Project phase Residual risk rating Category Potential event Construction stage excavations cause ground movement Damage to rail lines resulting in disruption of services Construction 2 – Western portal 1 – Tunnels (western portal to Arden station) Medium Construction stage excavations cause ground movement Damage to tram lines resulting in disruption to services Construction 6 – CBD South station Medium Construction stage excavations cause ground movement Damage to Telstra Tunnels resulting in disruption to key infrastructure Construction 6 – CBD South station Medium Tunnel construction encountering rock with greater rock mass strength than expected May necessitate a change in construction methods in a zone of geological conditions leading to increased ground movement or cause TBM to go off-line. Requirement to change construction method or repair/retool TBM could result in project delays Construction 1 – Tunnels (western portal to Arden station, Arden station to Parkville station, CBD South station to Domain station) 2 – Western portal 3 – Arden station Medium Ground heave as a result of excessive face pressure by the TBMs in shallow cover areas Unacceptable ground movement Construction 1 – Tunnels (All) 2 – Western portal Medium The assessment has been based upon a review of the ground conditions and preliminary modelling that provides a conservative estimate of the potential settlement values, their distribution and their effects on structures and civil infrastructure. The risk register was developed with the geotechnical risks associated with geological variability in mind and the potential for excavations to encounter unforeseen/unexpected conditions. The levels of confidence in the current interpreted geological model are reflected in the current register. Ongoing geotechnical and hydrogeological investigations would allow refinement of the model and increase levels of confidence in those areas identified as having medium residual risk ratings, potentially reducing them to low.
MMRP_Chapter-19_Ground-Movement.docx