A creative approach was required to dewater a 17km pipeline, up to 110 meters below Sydney, to ensure its integrity while major state infrastructure works are completed nearby.
Built in the early 1900’s, the Sydney Water Pressure Tunnel is a 17km long steel pipeline, laid 46 to 110 meters’ underground.
The tunnel was last inspected in 1993, with very few records remaining to show how it was done. Much of the original plant has been decommissioned and removed.
With tunnel boring for major state infrastructure projects WestConnex and the Sydney Metro underway nearby, Sydney Water brought the inspection schedule forward by several years.
They engaged the Atlas team to rapidly establish a safe and effective means of dewatering the tunnel, to facilitate inspections and installation of monitoring equipment.
Sydney Water says an inspection like this normally requires up to two years of planning, but in this case, we were able to fast-track the dewatering to help the client carry out a successful inspection in just nine-months.
Innovations from the Atlas team to help facilitate this timeline included:
Historical image showing a cross-section of the Sydney Pressure Tunnel. Source: Sydney Water
- Using high flow and pressure borehole type pumps to minimise dewatering time of the potable water.
- Development of bespoke steelwork arrangements to mount bore and drainage pump pipework.
- Application of a dummy pump to enable a low risk clearance check in the shaft pipework prior to installing pumps.
- Using high pressure flexible polyurethane composite pipework and specialised fittings designed to suspend the pumps and lower them through bends in the tunnel shafts.
- Carrying out FEA stress analysis of the tunnel to evaluate maximum external pressure on the drained tunnel from the groundwater table.
- Establishment, specification and sourcing of temporary power, variable speed drives and level instrumentation from inception to delivery to site within a few weeks.
- Design of re-useable plant and equipment.
Tunnel buckling pressure analysis
Shaft 5 model
Dewatering of the tunnel allowed Sydney Water to ensure the integrity of this critical asset and safeguard it while major infrastructure works occur nearby.
The client was able to carry out a trial shutdown, inspect conditions and survey the tunnel to confirm levels and location. And, in a first for Sydney Water, they were able to instal Fibre Optic strain sensors at joints along key sections of the tunnel to monitor its integrity before, during and after the transport tunnelling works.
Additionally, Sydney Water now has a proven methodology and plan to dewater the tunnel using the same equipment in future.
The challenges presented by brownfield site infrastructure can feel never-ending, but a steady, experienced and innovative team will ensure a successful outcome.