NZ Geomechanics News

Branch Reports

Northland Branch Report

Northland Branch Whangarei Geotechnical Issues
How Council is managing geotechnical hazards and risk and learnings form review of geotechnical reports.

The talk covered:
Councils RMA process, Building Consent process Learnings from T&T reviews, Hazard Maps, councils goals, and practice fields and competency.
Council has found from processing consents that most sites are now in the high to moderate stability hazards zone and there has been active landslides on recent developments.
Council has identified issues and shortfalls with geotechnical experience and competency of the persons preparing the reports.
Council is now undertaking peer review of all geotechnical reports on high stability risk sites.
The learnings from these reviews were:

  • No deep investigation and reliance on hand augers
  • No discussion on groundwater
  • Expansivity was visually assessed
  • Settlement was not considered or discussed
  • Inadequate discussion of obvious visual issues
  • Insufficient design information
  • High risk slopes with no slope analysis
  • No laboratory testing or back analysis

The current hazard maps currently being updated and will be extended to the unmapped areas.

The council is wanting to bring geotechnical practices in line with “good practice”. This can be using the WDCEES2010 as a guide with the outcome to reduce the likelihood of future failures and manage risks to council, developers and homeowners. This will provide a more good quality piece of min housing stock.

There are concerns with the people supplying and signing off geotechnical reports who are not within CPENG (geotechnical) or PEngGeol. Going forward for Moderate to High risk sites the engineer must be a geo professional.

On 2 June the Northland Branch hosted an online talk titled “Landslips in Northland, Observations from Select Case Studies”. The talk had a fantastic attendance with more than ten times the number of Northland Branch members listening in. The talk comprised a tour starting with two landslips in Auckland then a clockwise circuit of eight landslips around Northland. The talk discussed how each of the landslips may have been identified, or if they were less obvious, signs in the landscape that indicated they were in a high risk area.

The use of QGIS to create terrain models with aerial and geological map overlays was also presented. QGIS is open source (free) and LiDAR for all of Northland is imminent so this will soon be a readily available tool for any site in Northland. The creation of red/blue anaglyphs from aerial photo stereo pairs sourced from to allow onscreen viewing, zooming and panning was overviewed. Red/blue glasses can be purchased on Trademe and free software to create the anaglyphs can be found here:

The talk finished up with some comments on stability hazard zoning studies, some pictures of Northland Allochthon rock samples, a challenge to complete a quick desktop scope of any site at the start of every job and some of the presenters thoughts. The talk was recorded and a link should be available.

Northland Branch is working on the following upcoming presentations with final dates to be confirmed as we welcome sharing to interested professionals.

1. 22 June. Guideline minimum geotechnical investigations and qualifications for land stability and foundation assessments
2. 13th July 2020 at 4:45 Geophysical investigation Introduction for geotechnical and environmental engineering applications

Auckland Branch Report

Above Professor Jonathan P. Stewart answering questions at the end of his talk in February

The Auckland Branch has had an eventful first half of 2020, with a number of international speakers presenting interesting talks earlier in the year. This was then followed by a change in tac to ensure pre-planned events could still be offered to members, with the introduction of well-known restrictions around socialising and travel. This has kept the team busy, requiring a rethink of presentation format and collaboration with Engineering New Zealand.

A couple of highlight talks earlier in the year were “Quantitative risk analysis of fragmental rockfalls” and “Seismic Pressures on Retaining Walls based on SSI Principles”, presented in person by international speakers Prof. Jordi Corominas and Prof. Jonathan P. Stewart, respectively. These talks were well attended by local geotechnical practitioners, with higher numbers than normally expected making short work of the generous pre-talk food and drink provided by Geotechnics and Geofabrics for the two talks respectively. Amidst the disruption caused by the Covid-19 pandemic, Nick Rogers was due to present the keenly anticipated talk “Shrink/Swell Testing of Expansive (Reactive) Soils – A Critical Analysis”. With the inability to present this as intended at the University of Auckland, the branch got to work, and in collaboration with Engineering New Zealand identified an opportunity to open it to the wider NZGS membership throughout Australasia via a Microsoft Teams Live Event. The talk was a great success with a very engaged 450+ strong audience posing plenty of questions to Nick at the end of the talk. The branch would like to thank Holly Rausch and Rebecca Mather from Engineering NZ for providing much needed IT support in setting up and running the Teams Live Event. The branch is hopeful that additional talks can be presented in this format and are currently seeking further topics and speakers.On another note, Ben, Chris and Jay would like to express their gratitude to Eric Torvelainen, who earlier in the year decided to step away from the role of Auckland Branch Coordinator. Eric has well and truly made his contribution to the Branch, with many years of valuable input and countless hours organising various events for members. He will be very much missed on the Branch Coordinators team, however, we look forward to seeing him at upcoming events and wish him all the best for future roles that he will no doubt hold.

Auckland Branch Coordinators,
Ben, Chris & Jay



NZ Geomechanics News
NZ Geomechanics News>Issue 99 – June 2020
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