A technically complex deep shaft excavation constructed in the heart of Melbourne’s CBD, requiring advanced geotechnical analysis and 3D numerical modelling to support the design of a temporary access shaft that would later be undermined during construction of the Town Hall Station cavern.
Client
Cross Yarra Partnership (CYP)
Location
Melbourne CBD, Victoria
Sector
Infrastructure & Transport
Services Delivered
2D and 3D Geotechnical AnalysisConstructability Reviews and Construction Phase SupportTunnel Access Shaft Design
The challenge.
The Latrobe Street Shaft formed a critical component of the Melbourne Metro Rail Project, providing access for excavation of an adit into the future Town Hall underground station. The 25 m deep, 18 m diameter D-shaped shaft comprised contiguous bored pile walls supported by ring beams installed progressively during excavation. Located within a dense urban environment, the design had to accommodate variable fill over Melbourne Mudstone, nearby buildings, former basements and foundations, as well as future mining through the eastern shaft wall. Tight displacement tolerances and limited geotechnical data added further complexity.
The approach.
FSG provided geotechnical engineering services throughout design development and construction planning. The team participated in design workshops to establish shaft geometry, construction sequencing and geotechnical design parameters. Initial feasibility and preliminary design assessments were undertaken using 2D geotechnical modelling before advanced PLAXIS 3D numerical modelling was completed to assess shaft wall behaviour, ring beam loading, soil-structure interaction and ground movements. Particular attention was given to predicting displacement impacts and assessing the future tunnelling activities that would penetrate the shaft wall during construction of the station access adit.
The outcome.
FSG delivered a robust geotechnical design framework that supported the successful design and planning of this critical temporary works structure. Advanced modelling enabled the project team to quantify settlement risks, assess future tunnelling impacts and optimise construction sequencing. The result was a practical and buildable solution that protected adjacent assets while satisfying the demanding technical requirements of one of Melbourne’s largest infrastructure projects.