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Customer:
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Wellington Water
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Consultant
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Stantec |
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Date:
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November 2022
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Capability:
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Mobile Plant Fleet,Underground Services,Traffic Management,Connections,Dynamic Pipe Bursting,Deep Trenches, Dewatering, PE Welding |
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Customer type:
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Government & Local Government
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Scope:
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Installation of approx. 440m 450OD PE100 SDR17 wastewater rising main by open trenching on Whitmore & Bowen St in Wellington’s busy CBD.
Installation of approx. 60m of rising main under the Lambton Quay intersection by pipe ramming. A challenging crossing of The Terrace intersection around congested existing underground services.
A complex connection to the existing wastewater interceptor at approximately 6m deep in Bowen St.
Remodelling of Pump Station 9, connection of the new rising main and enabling works for future stages. All testing and commissioning activities.
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There were multiple challenges and risks involved in this major piece of work as part of a wider programme to upgrade the CBD's wastewater system. These included working safely in a constrained CBD environment where management of traffic, underground services and groundwater were particularly complex and with the need to manage a high-profile stakeholder environment including Parliament, The Reserve Bank, The Supreme Court & Victoria University.
We addressed these through a collaborative, innovative and rigorous approach to deliver the best outcome for Wellington city. This resulted in this project winning a CCNZ 2022 Award.
Solutions to challenges
We planned and delivered all aspects of traffic management in the city's busy CBD working closely with RCA throughout.
Deep trenching of over 4m deep below the water table in reclaimed contaminated land was well managed on site with safe shoring solutions, correct soil management and effective dewatering.
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Deep open trenching below the water table.
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To cross busy intersections including Lambton Quay and the Terrace, we applied the most appropriate solution to each location. Pipe ramming under the Lambton Quay intersection to eliminate the need to excavated under complex traffic management and around significant underground services. This significantly reduced disruption caused by the project and delivered a lower risk, lower waste solution.
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Pipe ramming under the Lambton Quay intersection.
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Open trenching was required across The Terrace intersection around heavily congested existing services and under extremely tight traffic management conditions, requiring the team to be disciplined about site set up and flexible around changes to alignments and grades.
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Congested services across The Terrace intersection.
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To install a connection to a critical ageing wastewater interceptor asset, we worked closely with Stantec to design a robust, buildable connection that would not compromise the integrity of the existing interceptor either during construction or in service. This involved sinking a shaft adjacent to the structure and making a connection at almost 6m deep. This connection shaft was then lined with GRP and fitted with a vortex flow control device to minimise issues associated with H2S attack.
To commission the network around the existing pump station infrastructure, we remodeled the interior of a pump station allowing the new rising main to be brought online alongside the existing rising mains. We then carried out enabling works so that the existing rising main could be treated in a following phase.