Linfield Park to Woolston Wastewater Pipeline Replacement

Scope‍

• 1350m of DN 1200mm Maskells GRP wastewater pressure pipeline
• 200m of DN 150mm gravity trunk main replacement by pipebursting
• 200m of DN 150mm PVC gravity collector main
• City stormwater culvert crossing
• Installation of pressure test stop ends
• 4 No. pipeline connections
• Connection to existing Pump Station 11

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Project description

This high-profile SCIRT project involved the construction of a new 3.6km 1,200mm diameter reinforced fibreglass pipeline from Bromley’s Linfield Park to a repaired pump station in Woolston. The pipeline had to be laid to very strict tolerance levels, both line and level as well as compaction. The new installation replaced two existing wastewater pipelines, which together serviced approximately 30% of the city’s wastewater.

While we were initially engaged by Downer to complete Section 4, our team was also awarded the balance of Section 3 and pipeline connections between the different stages of the contract. This was in recognition of our outstanding performance and productivity.

Collectively, our role across the three project stages comprised installation of 4000m of pipe work and the tie-in of Pump Station 11to the existing wastewater treatment plant.

Our methodology was based on pipe installation in 6m lengths into silty sands using well-point dewatering to lower the ground water table. We used a combination of specially designed and manufactured shields and sheet piles to shore the excavations.

Ground conditions in this area of Christchurch meant the ground was extremely hard to dewater. To address this, we devised a methodology which utilised custom-designed plastic well-points and localised wells which we installed as the trench progressed.

Other challenges included dealing with the city stormwater outfall crossing, installation of large pre-manufactured pipe bends, the complexity of the Linwood Avenue intersection crossing and a 66kV power crossing (which required a specially designed and fabricated GRP pipe), pipe pressure test cap removal and connections, and the tie-in to Pump Station 11.

Despite the complexities and challenges of this exceptionally difficult project, we delivered within programme and budget. These outcomes were achieved by deploying the right people onsite with the right skills and the right resources at their disposal.