Ngauranga Gorge pipe connection seismic upgrade

We’re de-watering the site to lower the water table in the area so the five-metre-deep pits we dig for the new geoflex pipe connections either side of the concrete chamber are not waterlogged.

Tests show the dewatering is working.

We expect to complete digging the first pit and lay concrete in its base by the end of May and install the geoflex connection in early June. We will then partially backfill that pit before we dig the second pit. The second pit is due to be dug by the end of June and the second geoflex pipe will be installed in early July.  

The pits will then be filled in and the retaining piles removed, and the site tidied up by mid-August.

Once the water wells work has been completed, which we anticipate being Thursday 16 April, we will be starting on installing the H (or bearing) piles.

H piles are structural steel beams shaped like the letter "H" that are driven deep into the ground to provide foundation support for heavy structures, acting as sturdy columns that transfer loads down to stable soil or rock, and in this case, will be used as retaining walls. They will have timber or steel plates (lagging) installed between them to retain the existing ground and make sure we can work safely in the deep excavations. The piles and lagging will be removed again once the work in the trench has been completed.

We expect the pile driving work to be finished by 24 April.

As the piles are long and need to be installed close to the road, the safest time is overnight during a road closure. Pile driving can be noisy and create vibration; however we will mitigate as much as practicable to reduce disruption.

Please follow the detour signage and take care if you are travelling through the area.

Work has kicked off to upgrade the critical pipeline at Ngauranga Gorge. This pipe brings water from the Hutt Valley into Wellington.

The site has been set up with safety barriers now installed.

Site establishment has been completed, including the installation of safety barriers to allow the crew to carry out works safely. 

Crews onsite working on the equipment for the ground water management night works coming up.

• From 9 pm to 4 am between Sunday 12 April until Thursday 16 April, we'll be working on the water wells to ensure the ground water levels are managed throughout this project.

• During this time, there will be some noise and vibration which we'll minimise as much as possible.

• Please follow signage and take care if you’re travelling through the area.

Wellington Water, on behalf of Greater Wellington Regional Council, will soon be working to install an earthquake resilient pipe connection at Ngauranga Gorge. This key pipeline brings water from Hutt Valley to Wellington City. Work is scheduled to start on 23 March and completed by 20 July.

Once the new pipe connection is installed, it will increase the pipeline’s ability to absorb differential movements during an earthquake, providing additional protection to the pipe. This is particularly crucial as this connection runs parallel to the Wellington Fault and could be vulnerable during a major earthquake.

During this work there will be periods when the SH2 slip lane from Hutt Road will be closed overnight (8pm till 6am). Please follow the indicated detour which takes traffic up the SH1 a short distance towards Porirua with a turnaround to direct traffic back towards the Ngauranga interchange. The bus stop will be closed for this period of work. Please follow signage and drive with caution while driving through this section.        

Road closures will take place between 8pm and 6am:

• overnight between 22 March and 2 April - to install additional guardrails at the work site
• between  15 April and 21 April – there will be approximately 5 nights work within this timeframe to install long stabilisation piles which allow us to safely excavate the pipe. 

This work is likely to create some noise disturbance however we will endeavour to reduce this where possible.

Water shutdowns of the pipe are scheduled for  11 June and 25 June. These shutdowns will not impact the water supply as there is reliable local storage. These shutdowns will begin in the early hours of the morning and require temporary traffic management to allow us to operate the valves safely. No lane closures are required while the pipe connection installation is underway.  

There will be further improvement works at the Ngauranga Interchange in the coming months by multiple agencies and contractors. Information about these works will be communicated with you closer to when the scheduled works are starting.

If you have any questions about this project, please contact: 
Jonathan Eweg, Design Lead on 027688 1917.