The Design Approach to the Cross-Harbour Pipeline, Wellington, New Zealand

The existing water supply to Wellington (New Zealand’s Capital City) relies on water transmission pipelines that cross the active Wellington Faultline in several locations. These pipelines are expected to break or sustain significant damage in a major Wellington Fault rupture event resulting in extensive parts of Wellington being left without water for up to 100 days whilst repairs are completed. The construction of a Cross-Harbour Pipeline (CHP) (approximately 800 mm diameter and 20 km in length) will significantly improve the disaster resilience and the operational resilience of Wellington’s water supply by providing an alternative pipeline route that does not cross the Wellington Fault. An innovative design approach was required that involved significant geotechnical work at an early stage in the project life cycle to inform the selection of a resilient pipe route and pipe design. This paper will discuss how an approach to a lifelines pipe route selection process was developed (to assess over 700 routes); that was informed by considerable geotechnical assessment and targeted site investigations at an early stage in the project, such that pipe routes being considered were the most resilient available (a primary project objective).