Challenges
- Construction of a grade separate south bound freight line beneath three heavily trafficked electrified suburban railway lines, without disrupting service to the North Sydney rail network
- Navigating surface rock outcrops on the east embankments
- Ensuring minimal disturbance to surface settlement
Solutions
Appointed by Transport for New South Wales as technical advisor sub-consultants for the concept design phase, several alternate underpass construction options were assessed with the primary aim of eliminating the previously selected cut-and-cover approach to reduce constructions time and disruption to mainline services above the underpass.
Drawing on finite element analysis (2D and 3D) and the multidisciplinary engineering expertise of our team, we demonstrated the feasibility of the driven tunnel option.
The selected tunnel option included movement of the tunnel alignment north by 60m, resulting in more favourable geological conditions and a deeper tunnel situated directly beneath the operational railway lines.
Construction commenced by inserting arrays of 12m long canopy tubes ahead of the tunnel under the operational tracks above, allowing full construction of the driven tunnel with a one pass shotcrete lining within an 8-month period with no disruption to train services.
Value and benefits
- Our driven tunnel option dramatically reduced construction time to just eight months compared with three to five years that would have been required for a cut and cover tunnel design.
- This design resulted in no disruption to the above three live trainline services during construction of the tunnel.
- Our team drew on extensive skills and experience gained from projects, highlighting three projects specifically as case studies to demonstrate the feasibility of a driven tunnel as a suitable design option.