Earthquake Geotechnical Engineering Practice Series – Now published

- Olivia Gill

NZGS proudly announces that the Earthquake Geotechnical Engineering Practice Series, commonly known as the Geotechnical Modules, have now been published in their final version.

The “Modules Finalisation Project” involved the update of the Geotechnical Modules that we have been using  as Preliminary (Version 0) since 2016, to incorporate new scientific knowledge and feedback received from the geotechnical community. The project was funded and led by the Ministry of Business, Innovation and Employment (MBIE) and was carried out with the collaboration of the three organisations, MBIE, Engineering New Zealand and the New Zealand Geotechnical Society.

It has been a tremendous effort by the team involved, and I would like to thank everyone that provided input, authors, reviewers and editors. I would like in particular to thank the past Chairs of NZGS Charlie Price, Tony Fairclough and Ross Roberts, for their efforts during their term and beyond to progress the Modules, and Mike Stannard, who coordinated the project.

The Modules were released on 29 November 2021 as part of MBIE’s annual updates to the Building Code. They are not regulation but have regulatory status in that they are guidance under Section 175 of the Building Act. This means consenting authorities can use them to support decision making when issuing building consents.

You can access the Modules through the NZGS website here and through the MBIE website here.

Important notes about Module 1, Version 1 – Updated seismic hazard

Following the lessons learnt from the Canterbury and Kaikoura earthquakes, Earthquake Commission and Waka Kotahi commissioned a study to research the latest seismic hazard. This was delivered by Professor Brendon Bradley at the University of Canterbury, as part of the Modules finalisation project, and is known as the ‘Bradley Study’ (2020). The Bradley study found that most New Zealand locations have a hazard which is comparable to that referenced in regulation. However, in six locations, the seismic hazard is likely to be considerably higher than that given in current legislation, namely Wellington (1.7), Gisborne (>2), and Blenheim, Napier, Palmerston North and Whanganui (1.4). The increased seismic hazard values are incorporated into the revised Geotechnical Modules on an interim basis until decisions are made about results, due in August 2022, from the National Seismic Hazard Model project.

The study only considered geotechnical hazard parameters and not those used in structural engineering. Therefore the new values should not be used for structural design.
The minimum standards for structural design continue to be NZS 1170.5:2004.

The updated Module 1 does not apply to existing buildings for the purposes of earthquake-prone building legislation, i.e. there is no change to hazard assessments for existing buildings under Earthquake Prone Buildings legislation. Earthquake Prone Building decisions will continue to be based on the current NZS 1170.5: 2004 standard and the MBIE/NZGS Earthquake Geotechnical Engineering Module 1, Revision 0 (2016) (that used Bridge Manual geotechnical hazard values).

More details and information can be found on the MBIE website.

Way forward

NZGS will continue the collaboration with MBIE and Engineering New Zealand to organise training and workshops on the updated Modules, as well as to ensure that new knowledge will be incorporated in the documents in the future.

NZGS will collaborate with MBIE, NZSEE and SESOC to collate feedback and identify further issues for clarification in the application of the Modules.

If you have any feedback, comments or questions please contact buildingfeedback@mbie.govt.nz, or the NZGS at chair@nzgs.com or secretary@nzgs.com or your collaborating Technical Society.

Olivia Gill
Email - OliviaG@cmwgeo.com

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