New guidance on foundations and site investigation

Posted: 9 December 2016

MBIE and the New Zealand Geotechnical Society (NZGS) have jointly released two new geotechnical engineering guidance documents as part of the Earthquake Geotechnical Engineering Practice series.

The two new modules are:

  • Module 2: Geotechnical investigations for earthquake engineering.
  • Module 4: Earthquake resistant foundation design.

This joint guidance has been published as Building Act s175 guidance.

MBIE is seeking feedback on these documents, and geotechnical and structural engineers are encouraged to make use of these modules and return comments to modulefeedback@nzgs.org within six months for consideration by the editorial committee. Comments are also welcome from others working in earthquake engineering. Feedback may result in the modules being updated after the six-month period.

For Module 4, feedback during this public comment period will inform decisions about the future direction of B1/VM4 (verification method for foundation design). B1/VM4 has not been updated for some time and has quite limited application. It does not address liquefaction-prone sites or those with other stability issues.

Module 2

Module 2 provides guidance on appropriate investigations to assess the ground conditions to support the seismic design of new structures.

Module 4

Module 4 provides the principles for good foundation design, including up-to-date practice and implementation of Royal Commission recommendations. MBIE recommends that practitioners make themselves familiar with the module and apply the guideline principles in their designs.

Some aspects of Module 4 may be perceived as being inconsistent with B1/VM4, particularly those related to strength reduction factors. However, shallow footing design is mostly governed by settlement considerations in the serviceability case, so change will be minimal in these cases. For deep foundations, Module 4 references Australian Standard AS2159: 2009 to provide a risk-based approach to strength reduction factors.

Modules 2 and 4 are part of a series being developed in partnership by MBIE and NZGS. They have evolved from the single NZGS document published in July 2010 (Module 1 - Guidelines for the identification, assessment and mitigation of liquefaction hazards). Modules already published are:

  • Module 1: Overview
  • Module 3: Identification, assessment and mitigation of liquefaction hazards
  • Module 5A: Specification of ground improvement for residential properties in the Canterbury region

Modules on ground improvement and retaining wall design in the NZGS Earthquake Geotechnical Engineering series are scheduled for release in 2017.

Geotechnical guidelines has further information on the modules.

Geotechnical engineering education programme

A seminar series on Module 4 will be held at various centres around New Zealand in early 2017. This will be open to experienced professionals and cover foundation design and include worked examples.

An online presentation covering the content of Module 5A ‘Specifications for Ground Improvement in residential areas prone to liquefaction’ is now available on Engineering New Zealand's learning webpage. This is a free resource for geotechnical and related professionals.

If you view the presentation and take a quiz you can claim this as Continuing Professional Development (CPD) hours. You will need to register to access the module.

This learning module is the first release of a joint education initiative between MBIE, Engineering New Zealand and the NZGS. It will run over the next few years.

Module 5A: Specifications for ground improvement

View the geotechnical educational programme

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: