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

Published: | Category: Technical advice note | Audiences: Road traffic engineers & consultants, Roading contractors

This note sets out the design requirements for  geosynthetic reinforcement-to-facing connections on mechanically stabilised earth (MSE) structures during seismic events.

Publication details

  • Author:
  • Published: 15 September 2021
  • Reference: 21-13
  • Contact:


This note sets out the design requirements for  geosynthetic reinforcement-to-facing connections on mechanically stabilised earth (MSE) structures during seismic events. 

The note is aimed at all contractors and consultants working on Waka Kotahi NZ Transport Agency infrastructure projects, and outlines the immediate change in expectations for design, pending the next Bridge manual update. These requirements shall apply from the date of publication of this notice.

General information

A risk has been identified for MSE reinforcing elements to separate from the facing during vertical movements in a seismic event.  It is not clear that this potential design risk is being fully addressed so it is necessary for Waka Kotahi to expressly restate the desired outcomes it expects from its suppliers.

Intent of the update

This notice requires all those involved in the design of MSE structures to ensure that this risk is mitigated through the design process.   Waka Kotahi must make certain that its practices protect public safety, deliver proper value and do not cause medium term issues that are likely to increase whole of life costs or potential premature failure of structures.

The intent is to confirm Waka Kotahi expectations, advise the issues that have been identified, and outline the action required to mitigate the potential failure.  This will allow our suppliers to be more aware of our expectations for the importance of suitable design of structural features both in this specific instance and in general.


Designers are required to ensure MSE reinforcing elements do not become separated from the facing during vertical movements, for the determined design accelerations in a seismic event, as part of their design process, for the stated design working  life. This applies in all cases where a facing is included whether or not it is technically part of the retaining structure.

Communication plan

Our target audience for this note is Waka Kotahi infrastructure delivery teams, designers, physical works contract procurement/purchasing teams and supply chain organisations delivering infrastructure investment and maintenance projects.

Advice of these changes will be promulgated by:

  • using all channels to advise the change in design expectations
  • direct communication through design contract processes
  • direct access to additional and further information via the website and intranet
  • delivery of presentations at the next Project Managers and Maintenance Managers Fora and the Procurement Fortnightly Hui.


The implementation should be fairly simple as it is targeted at a specific and limited audience.  These are established processes that should already be in effect The aim is to ensure that better outcomes are more consistently delivered as a result of utilising this communication exercise.

Given this update is aimed at a particular audience, it was not considered necessary to conduct company-wide, specific training on the changes.

Document review

It is important to check that this has been delivered effectively and the desired outcome achieved.  A review of the effectiveness of the changes will be undertaken by sampling the designs used for a number of structures used in road construction projects.  Should the identified issues continue to appear, a larger sample will be taken to establish the problem size and a further communication exercise will be undertaken.  Training may also be considered.

Publication details

Author: Waka Kotahi NZ Transport Agency
Published: August 2021
Version: 1
Location: Technical advice note | Waka Kotahi NZ Transport Agency (

Further information

If you have any questions or feedback, please contact the Lead Advisor at



Greg Haldane
Chair, Ratification Group

Vanessa Browne
Delegated Approver


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