Reinstatement of as much water storage as feasible was urgently required following the February 2011 earthquake, which severely damaged the Huntsbury Reservoir, resulting in the total loss of stored water from the 35,000m3 structure, a vital piece of Christchurch infrastructure.
Preliminary investigations revealed an unknown ‘shear zone’ through the reservoir site, the presence of which dramatically influenced the reinstatement design, and intensified deadline pressures around providing water storage capacity before the next peak summer demand.
The design and construction methodology adopted for the challenging site enabled the reuse of the concrete external walls, roof slab, foundations and floor slab of the existing structure, resulting in two separate tanks on either side of the shear zone. Works to add seismic resilience to the structure were designed to incorporate these retained concrete components.
The reuse of demolition concrete waste was also crucial to the material minimisation plan. Demolition concrete was crushed on site and reused as fill in various locations, while further reductions in material waste and vehicle movements were achieved through stockpiling on site.
In conjunction with the reuse of existing components and waste material, a staged approach to construction, which saw the two new reservoir tanks constructed in sequence, followed by the demolition of the structure and landscaping of the area between, greatly assisted in the prompt re-establishment of water storage capacity.
The rapid reinstatement of water storage prior to the peak summer demand was critical for the residents of Christchurch in the period after the earthquake events. Complementing its practical benefits, site development at this civil amenity has been left deliberately open, grassed and landscaped for potential leisure use by the community.
William MacManus of Fulton Hogan Ltd accepts the Excellence in Civil
Construction Award from CCANZ Chair Ross Pickworth