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Resilience features of the Christchurch Rebuild

FEATURES: Line of Defence, April 2016

Triumphal Arch, Christchurch.Triumphal Arch, Christchurch.

 

A civic memorial service held in Christchurch to commemorate the 185 people that died during the February 2011 earthquake marked five years since the disaster. It was also a solemn reminder that the clearest and most present dangers facing New Zealand come not from beyond our shores but from forces of nature acting within them.

While much of the media surrounding the Christchurch rebuild has focused on the issues facing home owners and businesses and the progress of multimillion dollar civic developments, there has been relatively scant focus on how the city is positioning itself to defend against possible future disaster events. That being said, a number of agencies and government-private collaborations are focused on the very task of rebuilding a more resilient Christchurch.

Ironically, the destruction wrought by the earthquakes of 2011 has provided the city with an opportunity to rise again more resilient than before, and to incorporate into its rebuild world leading infrastructural resilience. In this article we review the application of resilience and safety principles into the rebuild from the perspectives of the Stronger Christchurch Infrastructure Rebuilt Team (SCIRT).

Resilient infrastructure

The Stronger Christchurch Infrastructure Rebuilt Team (SCIRT) is based on an alliance agreement between the Christchurch City Council, the New Zealand Government and five delivery teams – Fletcher, Fulton Hogan, City Care, Downer, McConnell Dowell - who are undertaking the repair work.

One of the key commitments of the alliance is to return the earthquake-damaged horizontal infrastructure assets to the Christchurch City Council in a more resilient state than they were before. According to Ian Campbell, SCIRT Executive General Manager, this commitment was recently tested. “The 14 February 5.7 earthquake was an unwelcome test of repairs to Christchurch’s damaged infrastructure, which stood up well. Checks of SCIRT’s more than 140 work sites did not identify any apparent damage.”

According to SCIRT, a key learning from the 2011 earthquakes is that the re-establishment of infrastructure as soon as possible after a disaster is vital to ensuring community resilience. It is therefore important that infrastructure can either withstand the event, or can be quickly reinstated after the event.

SCIRT examined how the infrastructure behaved and performed during the earthquakes and enhanced the standards and specifications in the areas where it found weakness and/or failure. These will be included in the Christchurch City Council’s standards and specifications.

 

Vacuum chambers being installed at Aranui.Vacuum chambers being installed at Aranui.

 

Underground pipes

An illustration of enhanced specifications is the replacement of a significant number of the old, fragile and damaged clay pipes with new, more flexible PVC (polyvinyl chloride) and PE (polyethylene) pipes which move with ground movement and do not fracture as easily as clay pipes can.

“Today, the decisions to rebuild stronger and more resilient pipes underground seem even wiser than ever before,” stated Mr Campbell. “I’m sure we are all grateful that foresight has stood us in good stead, and it would appear that by and large, our new and repaired infrastructure stood up well.”

Vacuum and pressure waste water system

In some parts of Christchurch, SCIRT is replacing the old gravity wastewater system with new systems. SCIRT has progressed the installation of a state-of-the-art vacuum wastewater systems in Aranui, and has completed a vacuum wastewater system in Shirley. It is also installing new pressure wastewater systems in parts of Parklands, New Brighton and Woolston.

The Aranui vacuum wastewater system is a three-year project which will service around 2,700 households and businesses when completed, and it is the largest such system in New Zealand. These systems are more resilient to movement because of the flexibility of the new pipes and they are easier to access and maintain because they are shallower systems, which are less susceptible to liquefaction.

Retaining walls

As for the pre-earthquake retaining walls, many were simply wall facings to prevent material loss from wet weather events. SCIRT has repaired these walls by establishing seismically stronger wall structures which are fixed into the ground with soil nails and very large ground anchors, typically 8 metres to 15 metres long, which are grouted into the wall to fix the retaining wall to the ground.

Pump stations

SCIRT conducted detailed assessments of where pump stations were damaged and failed and addressed those issues when it repaired or built new ones. For instance the ground around and underneath new pump stations was reinforced, some with stone columns, and SCIRT strengthened the connections of pipes to the pump station so the pipes flexed with the station structure rather than against them as some did in the earthquake.

To date SCIRT has repaired and rebuilt 63 wastewater pump stations and 21 fresh water pump stations and reservoirs.

Bridges

Bridges structures have been strengthened through modern day designs and materials and where they have been demolished and repaired they have been built to modern standards designed to flex with ground movement more than the old bridges.

Repairs to the iconic Christchurch war memorial, the Triumphal Arch, standing on the Bridge of Remembrance, included strengthening the columns from the inside with steel boxes and installing components that enable the structure to rock in an earthquake.

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