Video: Overview of the earthquake geotechnical guidelines

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Duration: 6.09 minutes

Hi, I’m Mike Stannard, Chief Engineer for the Ministry of Business, Innovation and Employment. Welcome to this introduction to the Earthquake Geotechnical Engineering Practice series.

Earthquake geotechnical engineering is a very important engineering discipline in New Zealand. We live with a high seismic hazard and we have a very complex geology and variable soil conditions.

If we are going to build safe, robust but affordable structures we need to understand the ground conditions on which they are built and we need to know how the ground is likely to behave in an earthquake.

This series of guidelines is being produced as a collaborative partnership between the New Zealand Geotechnical Society and MBIE. It is for practising geotechnical professionals who have a sound background in soil mechanics and earthquake engineering in New Zealand.

The intention is to improve overall New Zealand practice and to promote a consistent approach.

The New Zealand Geotechnical Society identified the need for these guidelines back in 2006. They released the first module, on liquefaction, in July 2010, shortly before the Darfield earthquake. Widespread liquefaction occurred and the module was timely and extremely useful for assessing future vulnerability in the affected areas.

The earthquakes and the Royal Commission recommendations further reinforced the need to provide better information and guidance.

Some modules in the series have already been published and others will be released progressively through 2017. There will be a number of documents, each focusing on different aspects of earthquake geotechnical engineering. It is intended that they will continue to develop and be kept up to date as new research results are produced and new design methods are advanced.

You can get an overview of the guidelines from Module 1 and also from this video.

I’ll now hand you over to Charlie Price, Chair of the New Zealand Geotechnical Society, who will run you through the modules.

Module 1, gives an overview of the guidelines. There is also some technical detail related to estimating ground motion parameters. Further work is being undertaken on this aspect and changes may be made to the recommended methods.

Module 2 covers ground investigation for seismic design. It includes discussion on the type and level of investigation required, which depends on:

    •  the site
    •  the scale and importance of the proposed structures
    •  and on the level of risk arising from a failure.

It explains the importance of creating a geotechnical site model, and includes planning of the investigations, investigation techniques, and recommendations for subsurface exploration and sampling. There’s also a section on preparing geotechnical reports.

Module 3 is about liquefaction hazards and their effect, including lateral spreading. Detailed guidance is given on the use of the ‘simplified procedure’ for assessing liquefaction risk. Sources of liquefaction-induced ground deformation are described and procedures for assessing ground deformation are outlined.

Module 4 deals with the seismic design of foundations. It includes discussion on the different types of foundations in common use together with a strategy for selecting the most suitable for each site. Both shallow and deep foundations are covered.

Module 5 covers the general topic of ground improvement. The various techniques and design methods are considered, and guidance is provided on assessing both the need for ground improvement and the extent of improvement required. The advantages and disadvantages of each method are indicated.

Module 5A provides a specification for designing and constructing ground improvement and includes the four main ground improvement techniques. It is specifically directed at ground improvement for liquefaction mitigation in residential properties in Canterbury. However, it will also be useful for other areas of New Zealand prone to liquefaction.

Module 6 will be about the design of retaining walls and will build on material already produced for residential retaining walls situated in the Christchurch Port Hills, extending it into more complex situations.

Other modules are also in the pipeline.

These guidelines provide ‘high level’ principles rather than being design handbooks. We are also developing worked examples to provide more detail, helping to demonstrate their practical application.

You can download all documents, at no cost, from the Geotechnical Society and MBIE Building Performance websites.

A Geotechnical Education programme, a joint venture between NZGS, IPENZ and MBIE, will support the release of the series. Educational resources are being created to assist with learning and understanding.

All the modules are being released with a period for user feedback before being finalised. It is important we get your feedback. We want to make sure the modules are not only technically correct but are also useful for you as geotechnical professionals.

Keep an eye on the Geotechnical Society and MBIE websites to keep up to date. We really encourage you all to make use of these resources.