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

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

This note confirms and refines the approval process and design requirements for geosynthetics used on Waka Kothi NZ Transport Agency (Waka Kotahi) projects.

Publication details

  • Author:
  • Published: 15 September 2021
  • Reference: 21-12
  • Contact:


This note confirms and refines the approval process and design requirements for geosynthetics used on Waka Kotahi NZ Transport Agency (Waka Kotahi) projects.

Background information

Design requirements and the approvals process for geosynthetics utilised on Waka Kotahi projects are detailed within the Bridge manual (Cl 6.8.1). This requires that only approved geosynthetics are used on Waka Kotahi projects.

Recently two potential issues have been noted, where the design and procurement of geosynthetics may not have complied with requirements set out in the Bridge manual.

Issue 1

Design parameters from trade literature or websites may have been utilised for design instead of the required parameters included with the approval certificate for the geosynthetics.

Issue 2

Alternate products may have been purchased for inclusion into the permanent works that do not have the same design critical values as approved geosynthetics.

Our requirements

Suppliers are reminded of our geosynthetic design and approval requirements in CL6.8.1 of the Bridge manual, including the requirement that only approved geosynthetics be used on Waka Kotahi projects. 

The following are refinements to the requirements of the Bridge manual:

  • Suppliers shall ensure that parameter values stated on the approval certificates are exclusively used in design.
  • Supplier’s purchasing/procurement teams shall formally check with designers that any geosynthetic being sourced satisfies the design parameters and values required by the design and will perform satisfactorily in-service for the design working life. 

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 refinements will be promulgated by:

  • this note confirming and refining our geosynthetics design and approvals requirements
  • newsletters to be used to communicate changes
  • delivery of presentations at the next Project Managers and Maintenance Managers Fora and the Procurement Fortnightly Hui.


The implementation should be simple as these are well-established processes that should currently be in effect.  The aim is to ensure these processes are consistently utilised using this communication exercise.

Given this update is a confirmation of current processes it was not considered necessary to conduct company-wide, specific training on the changes.

Document review 

It is important to check that this this has been delivered effectively and the desired outcome achieved.  A review of the effectiveness of the refinements will be undertaken by sampling the designs used for road construction projects employing geosynthetics.  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.  Should this continue to recur as an issue after that, further action will 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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