Design and monitoring, Sydney Metro Northwest, Australia
The $8.3 billion Sydney Metropolitan Northwest project is the first stage of the Sydney Metropolitan train line from Epping to Rouse Hill. It includes 15.5 km twin tunnels (Australia’s longest rail tunnels) and 4 km of elevated skytrain.
PSM was engaged to design the high-risk components of the Sydney Metro Northwest project which included five new cut-and-cover stations, three elevated stations, several enlarged openings at the tunnel station interfaces, and a rail crossover cavern at Castle Hill. PSM was also responsible for providing geotechnical services during the construction phase.
Engineering and technical opportunities
The PSM design included enlarged openings at the tunnel station interface with a narrow rock pillar between openings. Several of the large 25 m deep and 200 m long station boxes were within faulted shale.
The 23 m span, 160 m long Castle Hill cavern beneath a highly trafficked Roads and Maritime Services (RMS) road presented the highest construction risk to the project. There were also challenging geological conditions working in a fractured and faulted shale rock mass.
Engineering and technical opportunities for the cavern included:
- Large span excavation
- Low ground cover
- Close interaction with existing surface and tunnel rail in the Epping mined tunnels design.
approach and innovation
Following rigorous assessment and modelling, PSM`s tailored approach included:
- Excavation and design of the rail crossover cavern at Castle Hill
- Implementation of a monitoring program for the cavern
- Refinement of monitoring program during construction based on quality data and detailed geological mapping
- The PSM design included enlarged openings at the tunnel station interface with a narrow rock pillar between openings.
Excavation of the rail crossover cavern at Castle Hill was completed without damage to sensitive surface infrastructure or disruption to traffic. Implementation of monitoring instruments were successfully completed without any community complaints, client issues or utility strikes.
PSM completed all work safely, within budget and on time while meeting the requirements of the design and the contract. Refinements to the monitoring program resulted in significant time and cost savings for our client.