Issue 104 - December 2022

What’s On at Waka Kotahi

National Seismic Hazard Model (NSHM)

The updated NSHM incorporates revised ground shaking parameters based on new information and improved scientific techniques. The modelled outputs do not require an automatic change, however, to how our infrastructure is designed. The position of Waka Kotahi is that the newly released National Seismic Hazard Model (NSHM) does not immediately affect Waka Kotahi issued design standards and guidance, including the Bridge manual. 

Waka Kotahi is closely working with MBIE who is currently engaged with Engineering New Zealand and relevant technical societies to assess what changes to building design standards are required, and how to include the NSHM results in regulatory settings for new buildings. During this process Waka Kotahi will assess the implications for our infrastructure.

More information on the updated NSHM can be found on The Ministry of Business, Innovation and Employment – Hikina Whakatutuki (MBIE) website:

Reminder about TANs (Technical Advice Notes)

Technical advice notes are produced by Waka Kotahi to keep practioners aware of new releases, interim advice, changes and updates to technical information, specifications, legislation and so forth in relation to highway projects.

In addition to looking at design standards such as the Bridge manual, practioners should always check for applicable TANs. These are relatively easy to search with some degree of success. 

A recent problem has been identified resulting from our own efficiency! Changes or requirements covered in TANs that affect, for instance, the Bridge manual are incorporated into the next revision to that document. As a consequence, those TANs are then withdrawn and don’t come up when searched for in the general page. The issue with this is that projects are designed (generally) to the Bridge manual (in this case) applicable at the time of award. So, if an amendment of the Bridge manual follows the project award the TANs applicable to the previous version are gone! However, they are not, and you simply need to check the withdrawn TANs. Waka Kotahi is looking into how to avoid this unhappy situation going forward but be forewarned in the interim. 

Here’s a list of TANs applicable in the geotechnical space to help you out in the meantime: noting this is not exhaustive and there may be others applicable depending upon exactly what area of infrastructure you are working in. Find them all here:

#15-13 Geotechnical testing and investigations

#15-14 Concrete barriers used to temporarily detain rockfall and slope debris

#20-08 Use of GAP65 as a drainage medium to retaining and geotechnical structures

#20-09 Use of sonic drilling in ground investigations

#20-10 Use of hollow bar ground anchors and soil nails

#20-15 Use of timber poles for ground improvement

#21-12 Design and procurement of geosynthetics for soil reinforcement

#21-13 Seismic design of the facing-to-reinforcing connections for mechanically stabilised earth structures

#22-04 Release of Bridge manual 3rd edition amendment 4

#22-10 National Seismic Hazard Model and what it means for our design standards

Slope Assessed Risk Level Course(s)

The assessed risk level (ARL) accreditation courses for slope risk assessment and mitigation works identification are finally under way in February 2023 with two courses centred in the North Island. Future courses in the North and South Island are planned. Thanks to all for your patience whilst navigating through C-19! 

For those who administer the outcome of the ARL assessment, Waka Kotahi will be running a one-day session for network managers and others outlining what the system is, what the results mean and what to do with them. If this is you and you’re interested in attending, get in touch!

Those seeking more information can contact

Update on S6 Bridges, geotechnical structures and other significant structures inspection policy

An inspection policy specific to geotechnical structures has been through ratification and is about to be published. S7 Geotechnical structures inspection policy replaces the existing geotechnical aspects in S6 (Bridges, geotechnical structures and other significant structures inspection policy). 

S7 Geotechnical structures inspection policy sets out the requirements for the inspection of geotechnical structures on the state highway network and follows the philosophy of S6 and is generally comparable. Specific changes between them are the inclusion of terms and definitions that apply to the S7 policy; definition of geotechnical structures; categories of inspection applicable to geotechnical structures; inspection frequencies; reporting requirements and example pro-formas. It is anticipated that inspections will begin in the next NLTP period and increase in subsequent NLTP periods as more are ‘discovered’ and added to the asset data base.

The next phase of this process is an inspector’s course, somewhat similar to the bridge inspectors’ course but geotechnical structure focused. We are looking for interesting images of geotechnical structures under duress: if you have some, we’d be keen to hear from you: quick way to get your name in print (photo credit)!

Unstable slopes and rocks!

Draft guidance documents: Rockfall Protection Systems Maintenance Guide (an area where there is little to no guidance for works completed prior to 2020) and Rockfall Projection Structures Design Guide (to unify design approaches and methods which currently vary widely between designers with associated risk profiles for Waka Kotahi and supplement existing MBIE guidance) will soon be available for comment. Both documents relate to Waka Kotahi highway works though it is recognised they may be adopted by other parties. We are keen to align with other potential users and interested in any comments they may have. If you represent a local authority or other potential user, we’d be keen to hear from you to ensure we provided a ‘rounded’ document. Contact either myself or

Tags : #Waka Kotahi

Issue 104 - December 2022, NZ Geomechanics News
Stuart Finlan
Issue 104 - December 2022, NZ Geomechanics News
New Zealand
Project News / Case Study

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