Client:            Watercare Services Limited
Location:        Auckland, New Zealand
Contract:        D&C
Completion:        January 2010

Project Summary

This multi-discipline D&C project was for the replacement of a 90 year old sewage pipe crossing Hobson Bay, on Auckland's waterfront Tamaki Drive.  The tunnel offers greater sewerage capacity to cater for projected population growth in the area and prevents wastewater overflows into both the Bay and Waitemata Harbour basin, a popular swimming spot.  The replacement of the existing wastewater pipe also opens up the Bay for recreational boating.  The contract scope included:

• 3 km long, 3.8 m internal diameter tunnel driven approximately 30 m below the bay floor
• Construction of three shafts of approximately 35 m to 40 m in depth (23 m, 8 m & 10 m internal diameters), including considerable mechanical and electrical works
• Surface reticulation and connection works
• Demolition of the existing sewer pipeline

The Challenge

Key constraints included dealing with the unique geology of the area, operating quietly 24 hours a day on a site located in a residential area with imposed restrictions on traffic, operating noise, and visual impact.

The Solution
To minimise disruption to local residents in the construction area we developed an innovative noise reduction mechanism with a completely enclosed head house.  Tunnelling 30 m under the bay's mud and rock floor has also ensured minimal environmental disturbance during construction.  The project used a TBM by Lovat of Canada and construction techniques were designed for a combined firm rock and soft substrate. 

Key to Success

A collaborative effort, particularly in key areas such as tunnel lining design, allowed us to devise an optimum design that took into account construction costs.  We used a blend of local experts on the geology of the area and designers with international proven experience and knowledge in tunnel lining design.  Extensive QA practices ensured that equipment such as the TBM and overall project deliverables were delivered to standard and on time.

Project Stats

• 17 days ahead of schedule
• 75m long TBM weighing over 200 tonnes
• 112 manhours per week
• 157m per week progress rates
• 690t less CO2 emissions every year, equivalent to removing 150 cars from the road, by using the latest TBM technology to raise the alignment
• 13,000cu m capacity of sewage and water every hour

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