Customer: Christchurch City Council
Location: Christchurch, New Zealand
Contract Type: Design and Construct
This project is a demonstration of our commitment to complete the works despite difficult ground conditions and at our own risk.
Various solutions were developed in collaboration with the Designer and the Council to make the design more earthquake resilient and resolve the settlement issues.
The contract comprises two separate but connecting sewer lines, Western Interceptor and Fendalton Duplication. The Western Interceptor comprises 4 km of 1,350 mm diameter gravity sewer, installed using trenchless technology complete with manholes and requiring services relocation and settlement monitoring.
Fendalton comprises approximately 2 km of between 450 mm and 1,050 mm diameter sewer installed using traditional dig and lay methodology complete with manholes, services relocation, settlement monitoring and a pump station.
Our works included line installation under streams as well as in and around Hagley Park. As part of the microtunnelling works, we also installed a separation plant at South Hagley Park to separate the excavated material from the lubricating fluid used in the tunnel shaft. This work required extensive M&E and commissioning works in a site of environmental and recreational significance.
The February 22 earthquake in Christchurch had a major impact on works progress. Members of the MSU team assisted with the City’s emergency response, including rescuing several members of the public trapped in buildings adjacent to our works and emergency repair works following the quake. Nearly 25,000 manhours were spent on the repairs of 32 pump stations, sewers and rising mains before the emergency works were handed over to the rebuild team and works could recommence.
Due to the quakes and over 10,000 aftershocks, some areas of the project had settled or sunk more than 300 mm against the original datum and benchmarks. Moreover, sinking manholes caused some jacking pipes to crack due to shear forces acting upon the tunnel. Though settlement was encountered in the jacking shafts, a 65 m section of open cut trench on the Fendalton Duplication was by far the most problematic part of the job with up to 120 mm of settlement recorded.
More than 5 million hours have been completed LTI free. This milestone has been attained while delivering a complex, fast-track project with significant terrain, environmental, safety, logistical and stakeholder challenges.
Key to Success
Proactive safety management has contributed significantly to the project’s success. This has included a tailored project induction, timely and consistent communication with all stakeholders and innovative engineering solutions. These have been effective in mitigating risk to the workforce and general public. The depth of experience in similar works provided by long-term McConnell Dowell Thai and expatriate staff is also a key success factor.