Christchurch City Council lifelines: Performance of concrete potable water reservoirs in the February 2011 Christchurch earthquake
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On 22 February 2011 an earthquake measuring 6.3 on the Richter Scale occurred in Christchurch City resulting in widespread damage to buildings and infrastructure. Christchurch City Council (CCC) has an extensive potable water supply network including bulk storage and service reservoirs which provide water to approximately 320,000 residents. Inspections undertaken, following the 22 February earthquake, on 43 concrete reservoirs located on the Port Hills and Cashmere Hills areas noted varying extents of damage from nil through to major. Damaged roof to wall connections were observed in many reservoirs with damage to walls, base-slabs and internal columns limited to a few reservoirs only. Of the 43 reservoirs, complete functional failure occurred in only one, with reduced function and operation at other sites resulting from excessive leakage, necessity for emergency repairs, or associated pipe work damage. Those reservoirs currently out of operation for reinstatement, including Christchurch’s largest, account for approximately 40% of the network’s storage capacity. Overall, given the magnitude of earthquake accelerations that occurred on 22 February 2011, the reservoirs are considered to have performed remarkably well. Those in the Port Hills area nearest the earthquake epicentre, have expectedly, incurred the most damage. Reinstatement works, varying from minor crack injection and patch repair through to reconstruction and retrofit, have been developed appropriate to the extent of damage. CCC has prioritised reservoir repair to maximise available water supply for the 2011-2012 summer demand and this has required, in some instances, staging and deferring of reinstatement works. A summary of structural and functional performance, results of physical investigations and detailed seismic assessments, and common damage areas observed are presented in this paper along with the reinstatement options developed.