On 4 September 2010, Christchurch, New Zealand, was hit by a massive 7.1 magnitude earthquake.
A 6.3 magnitude quake followed on 22 February 2011, killing 185 people and damaging the city’s land, buildings and infrastructure.
Christchurch was affected again later that year when additional 6.3 magnitude and 5.6 magnitude quakes hit in June.
The earthquakes were the most severe to hit the region since 1888 and caused significant damage to the city’s underground infrastructure.
In 2011, the Stronger Christchurch Infrastructure Rebuild Team (SCIRT) was formed, tasked with managing the repairs to the horizontal infrastructure that was damaged by the earthquakes.
SCIRT was allocated NZ$2.2 billion to fund the management of around 700 projects across the city including repairing and rebuilding underground sewerage, stormwater, and fresh water pipes, rebuilding wastewater pump stations as well as roads, bridges and retaining walls.
The five-year SCIRT construction program started in September 2011 and will be completed by the end of this year. It has been co-funded by the New Zealand Government and the Christchurch City Council.
Many of the projects under the program have utilised no-dig methods including horizontal directional drilling, pipe bursting, pipe jacking and relining.
This uptake of trenchless is significant considering prior to the earthquakes the use of no-dig methods for large-scale projects was mainly confined to New Zealand’s biggest city, Auckland.
Some of the challenges of delivering the rehabilitation program included Christchurch’s high water table, swampy ground conditions and the variability in the settling of the ground after the earthquakes.
SCRIT work crews also had to deal with multiple aftershocks which continued for 15 months after the February 2011 earthquake.
About the program
By the time the program of repairs is completed in December, SCIRT will have completed 156 km of pipeline repairs in its program through the use of cured-in-place pipe (CIPP), spiral wound lining, and fold and form methods.
SCIRT figures have shown that pipelining has provided average savings of 30 per cent over the cost of digging trenches and laying new pipes.
SCIRT Executive General Manager Ian Campbell says pipelining was suitable for almost a quarter of the earthquake-damaged wastewater pipes in the SCIRT repair program.
“Pipelining is not suitable for repairing extensively damaged pipes or pipes where joints have come apart or pipes with large dips where debris can collect and form a blockage.
“Lining is really only used where the existing pipe is still in good enough condition to put a liner into it,” he explains.
In places where the infrastructure was too damaged to be considered for rehabilitation, SCRIT used a number of trenchless methods to install new pipes and has retrofitted several pressure sewer services to replace badly damaged existing gravity networks, thus providing more resilience in areas of Christchurch with poor ground conditions.
One particular project utilised horizontal directional drilling (HDD) to install a new 325 m, 400 mm wastewater pipe under the River Avon, in the suburb of Burwood.
Project Engineer, Dan Fryer explains “The rig used in Burwood is one of the most advanced pieces of equipment for HDD in the world today.
“It is the only one of its kind in New Zealand and the technology far exceeds anything currently available here.
“The HDD method is a cheaper alternative for tax and rate-payers, a faster means of installing pipe and is less disruptive because there is no need for road reinstatement.”
The installed pipe is more resilient to future earthquake damage because the alignment is at an acute angle to the river, which means that if the ground liquefies and the banks of the river collapse then the pipe can better withstand movement.
Experts from around the world were brought to New Zealand to assist with the work and also run tests on the rig and equipment, from as far away as Frankfurt, Perth and Essex.
The drilling work was successfully completed at the end of February and the pipe was recently put into action.
Looking to the future
The SCIRT construction program is now entering its final four months with over 94 per cent or repairs completed.
Since the program commenced in 2011 more than a third of Christchurch’s 1,770 km sewerage pipe network has been repaired or replaced, and 30 new pumps and 65 lift stations have been installed.
The design and layout of the new pipes has taken into consideration the effect that seismic activity can have on underground assets, with pipes being laid at shallower depths and at steeper slopes.
SCIRT has also overseen the design of a new vacuum wastewater system that can survive seismic activity, by flexing and moving with the ground.
The system uses suction instead of gravity to move wastewater, and has been connected to 2,700 homes and businesses in the suburb of Aranui.
In addition to this some 1,800 households now have pressure tanks underground which connect to new pipes in their streets.
As a result of the overhaul of the underground infrastructure Christchurch will now have one of the most modern sewerage and wastewater systems in New Zealand.
For more information visit the SCIRT website.
This article was featured in the September edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
If you have news you would like featured in Trenchless Australasia contact Assistant Editor Nick Lovering at nlovering@gs-press.com.au