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#20-02 Pilot specification for in-situ subgrade stabilisation

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

This note is to advise that the NZ Transport Agency (NZTA) Specification B/9P:2020, In-situ subgrade stabilisation, has been released for use on agreed pilot projects and is available for download from the Transport Agency’s website.

Publication details

  • Author:
  • Published: 14 February 2020
  • Reference: 20-02
  • Version: 1
  • Contact:


This note is to advise that the NZ Transport Agency (NZTA) Specification B/9P:2020, In-situ subgrade stabilisation, has been released for use on agreed pilot projects and is available for download from the Transport Agency’s website.

The new specification applies from the date of this notice to agreed pilot sites. 

The Transport Agency intends to review the findings from the pilot study, and then update and release the standard for general use for all for all in-situ stabilisation projects by mid-2022.

General information

The sector has a desire to reduce the use of non-renewal resources such as aggregates and bitumen.  In pavement design one of the most effective techniques to reducing resource use is to improve the materials that exist on site through subgrade stabilisation. However, there is no standard procedure for construction using these materials.

Currently each Design Engineer must produce their own construction specification with its own quality assurance regime.  This is a significant barrier to the widespread use of stabilised subgrades.

NZTA B/9 Pilot Specification, and its accompanying Notes document, is a new construction specification that the sector wishes to trial.   

The purpose of the document is to provide a standardised construction specification for stabilising subgrades. It has been developed by the National Pavement Technical Group (NPTG). 

The NPTG is a grouping of industry (Contractors, Consultants and local and central government Clients) pavement design specialists, along with representatives from the Aggregate and Quarry Association (AQA), the Civil Engineering Testing Association New Zealand (CETANZ), Civil Contractors NZ (CCNZ) and the Association of Consulting Engineers NZ (ACENZ).

The B/9P Specification has been developed by the NPTG. 

The specification has not introduced any new tests. 

The specification simply attempts to standardise and document the procedures currently used.

Version changes effective date

The new specification can replace current project specific requirements. 

The pilot B/9P shall be implemented immediately for use with new designs, and on existing physical works contracts by negotiation where required.

Please contact David Alabaster ( to register a trial of the B/9P specification.

Communications plan

Advice of this change will be promulgated by:

  • this note advising the pilot specification’s release
  • Industry newsletters including CCNZ and CETANZ
  • delivery of presentations at appropriate industry events (such as REAAA roadshows, CCNZ Conference etc).


Subgrade stabilisation is already a viable and used design option in pavement design via the Austroads Guide to Pavement Technology.   

The technology is particularly suited to new Greenfields built pavements. 

Project managers should be asking Pavement designers what consideration has been given to in-situ stabilisation in developing design report options.

The pilot process will be managed by David Alabaster. 

Projects will only be required to provide initial details about where, when and how they are stabilising. Quality assurance records for the pilot process will need to be collated into a pilot-specific database as the quality assurance records become available.  

The database must be accessible to client organisations using the statistical software package R to allow collation across projects. 

For more information on R visit link).

Document review

A review of the Pilot B/9 will be scheduled for two years after the issue to determine the uptake of the new version of the specification and identify any problems with its use.  The sector experts involved in specifying stabilised pavements, the NPTG and CETANZ groups will be canvassed for comments on the specification.

Publication details

Author: Waka Kotahi NZ Transport Agency
Published: January 2020
Version: 1
Found at: link)

Further information

To submit documents or if you have any questions or feedback, please contact the Technical Services team at



David Darwin - Chair, Ratification Group

Vanessa Browne - Delegated Approver