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Deans Head Remediation, Christchurch, New Zealand

Aurecon delivers unique, cutting-edge smart solution for the remediation of Deans Head, an earthquake-damaged cliff and landslide on the Port Hills of Christchurch, New Zealand

 

Video Transcript: Dean’s Head Remediation - Christchurch, New Zealand

Simon York, Advanced Design Technologist

So, one of the projects that I showed in AU this year was a site that came about because of the earthquakes that hit Christchurch about six years ago. It's a cliff site that used to have houses on it and, unfortunately, most of these houses were lost in the earthquake.

Our role in the project is to monitor that site as the site is remediated, so that means a lot of materials can be removed from that site to reshape the whole site. It soon became obvious that AUVs were going to be a pretty powerful tool in this project. Initially there was a use of abseilers to inspect the cliff, especially after any aftershocks that happened. We were able to quickly implement use of UAVs though to perform those visual inspections and the use of reality capture tools such as Recap and Remake from Autodesk, soon became really powerful to be able to use to capture photos from the UAVs and then run those through to create models of the site.

What are the benefits of this technology?

So much time saved in that process, also just the accuracy – the ability to have a real representation, a 3D model of that site, on a weekly basis so we can now go back over the last six months and actually see where things have changed the entire time. I've been trying to promote throughout the business, the use of reality capture tools on every project, not just open lands type projects. I see it as being hugely valuable for building services and building structures. The ability to capture the existing buildings and have that data available to you when you’re designing, but also in the construction process. So, why shouldn't we be scanning buildings weekly as they've been constructed so that we know what’s happened on the site week-to-week and see where the changes have happened.

As an aftermath of the Canterbury earthquakes in 2010 and 2011, the steeply sloping residential area of Deans Head in Sumner posed a serious threat to the access of the Sumner Township and potentially disrupting more than 7 000 residents. The strong earthquake shaking caused a repeated retreat of the cliff edge. Some 25 metres of cliff edge fell off the 80 metre high and 350 metre long cliff. The adjacent residential area of Deans Head was left in a badly cracked and unstable state. Deans Head was then identified to be a very large landslide in insipient mode of failure.

A temporary solution

The potential aftershocks and rainfall meant that risk remained high for further cliff collapse and landslides. The community faced the possibility of being isolated from Christchurch if the main road into Sumner, situated below the cliff, was cut off. A temporary solution was implemented to lessen the risk for road users; and fully ballasted, double stacked high shipping containers were placed in the highest risk areas.

The New Zealand Government, however, needed a feasible long-term solution which a traditional slope remediation solution could not provide. Eventually the removal of an estimated 53 000 cubic metres of landslide debris was considered, with some of the debris to be reused in the reserve for cliff collapse protection works.

To aid in the safe execution of this complex task, Aurecon was commissioned by Land Information New Zealand (LINZ) as the key advisor for all engineering services including civil, geotechnical, structural and surveying.

Using smart technology

Aurecon proposed and led a remediation project which entailed the removal of virtually all landslide debris from site and the creation of a catch ditch and rock bund for risk reduction, primarily for the main road users.

To enable construction work underneath the damaged cliff and on the unstable land, the project team engineered a unique, cutting-edge smart technology that laser scanned the cliff using photogrammetry and Unmanned Aerial Vehicles (UAVs). This innovative procedure is the first of its kind to be used in New Zealand to evaluate ground volume changes that involved:

Volume measurement

  • Weekly flights with 3DR Solo and DJI Phantom 4 drones to collect over 1 000 aerial high resolution (4k) images per flight of the site
  • Processing of images with Autodesk®ReCap™ photogrammetry software into a weekly three dimensional (3D) complex terrain model
  • Enhancing the accuracy of 3D models from 300 to 50 millimetres by incorporating ground control point data
  • Comparing each 3D model from the previous week to calculate the volume removal progress against earthmoving contractor estimates

Safety and work planning

  • Use of virtual reality (VR) headsets to view models visualising the project’s progress
  • Interrogation of the 3D models in augmented reality (AR) by using HoloLens headsets (the latest technology in AR), which allowed multiple engineers to view it simultaneously, and enabled discussion on the health and safety implications of the works and prediction of logistical hurdles and opportunities

Ultimately, the success of the project led to the reconnection of Christchurch communities, providing them with a new future and relieving them of the threat of being isolated by landslides, cliff collapse and rockfalls.

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