IPWEA Australasia Excellence Awards Winner: Best Public Works Project 2017 Under $2M

Recipient: Christchurch City Council and Fulton Hogan

Project: Sumner Road Retaining Wall, Stage 4

Sumner Road is an arterial road linking Lyttleton to Sumner, and an access road for several residents.

Its century-old retaining wall was weakened by the 2011 Christchurch earthquake, and targeted for repairs by the five-year SCIRT (Stronger Christchurch Infrastructure Rebuild Team) alliance.

Each of the five stages for the Sumner Road Retaining Wall repair have had different needs and different approaches. Stage 4 was originally going to be built with a bottom-up approach, but the steep slope and weakened wall meant this posed risks. Stage 4 was also directly above the Holcim site - then main source of Christchurch’s cement for the rebuild.

The design for a new approach had to factor in how weak the wall was and the un-safeness of loading it. A new way – using a gantry-lifted work access platform for installing 180 soil nails up to 8m-long – was needed.

“My in-house technical team and temporary works designers derived a scheme of working off a suspended platform, which is effectively a modified container which a drill rig was attached to and suspended over the edge of an 80-tonne crane,” says Tony Gallagher, General Manager Civil at Fulton Hogan.

The company’s nomination explains that the drill mast was mounted across the container, and a gantry crane positioning the drill rig at various locations on the platform “allowed the container to be positioned on the wall and tethered in place and multiple nails to be installed by simply moving the drill mast along the container without un-tethering the container.”

After soil nails, drainage was installed, footing dug and poured, and two layers of shotcrete applied.

The project was delivered ahead of schedule and under budget, with a nearly perfect daily ‘zero harm’ record throughout.

Gallagher applauds the team’s innovation in the face of pressures, and having the “courage to stop and critically review despite the pressures of time, and getting the right result.”

Stakeholder engagement was also a huge component of the job, he believes. This was complicated by factors including being an archaeological site (which turned up an ancient glass bottle) and flora and fauna sensitivities. A colony of Canterbury geckos that took up residence in a crack were rehomed by the Department of Conservation during the project.

Gallagher believes that, for him and his team, the greatest reward of the project was the satisfaction of the local community.

“When the local residents come up alongside the team and give the team some cookies and scones and cups of tea and coffee, and are grateful for the work as getting done,” he says.

“And they see that completed job as progress."