Rail tunnel design, Epping to Chatswood, NSW, Australia
The Epping to Chatswood rail link is a 13 km rail tunnel linking the northern region of Sydney to the Sydney central business district. Thiess and Hochtief were jointly awarded the $1.2 billion contract by the NSW Government to design and construct the tunnel. A key component of this project was the design and construction of the soft ground decline tunnel connecting the TBM tunnel to the surface at Chatswood.
PSM was engaged as part of the construction team to validate and monitor tunnel design, particularly for the major station caverns constructed with relatively shallow cover. PSM was also responsible for the design of the Chatswood dive structure including 170 m of twin tunnel to meet the surface and join the North Shore rail line north of Chatswood (constructed beneath the operating North Shore train line).
engineering AND technical opportunities
The tunnels pass through residual clays and extremely to highly weathered Ashfield shale. The tunnels have a depth of cover as low as 5 m. Constructed beneath the operating North Shore train line and near commercial infrastructure the tunnels have low overburden cover.
approach AND innovation
Following a rigorous assessment and modelling, PSM’s tailored approach included:
- Secondment of eight PSM personnel to the Thiess Hochtief joint venture to map and monitor
- Use of canopy tubes as temporary tunnel support in soft ground
- Modification of designs (if required) during tunnelling as ground conditions were exposed while maintaining a close relationship with construction team
- Development of 3D numerical models of construction sequencing and tunnel support
- Extensive monitoring of instrumentation of tunnels, existing rail and commercial infrastructure
- Detailed monitoring of instrumentation of the caverns to enable back analyses of the ground response to the cavern excavation.
PSM’s practical and innovative tunnel design for the Chatswood soft-ground portal ensured there was no disruption to existing rail and infrastructure. Geotechnical monitoring for the entire project was successfully completed.