Geotechnical outputs from the EQC – Quake Centre Industry Fellowship programme

Geotechnical outputs from the EQC – Quake Centre Industry Fellowship programme

The Earthquake Commission (EQC) has, for a long time, been an important investor in high quality research in New Zealand. EQC’s research programme spans science, engineering and social science and has played a vital role in supporting New Zealand’s improved resilience to natural hazards.  Through its support of the Quake Centre, a series of EQC-Quake Centre Industry Fellowships have been implemented over the past five years. The Industry Fellowship Programme is predominantly aimed at mid to late career engineers who have shown leadership in the industry. The purpose of the Fellowship is to allow experienced practitioners time to distil lessons they have learnt and develop tools or guidance that can be shared directly with the industry as a whole. This can be particularly valuable if the practitioner is able to engage with their academic colleagues to integrate new knowledge developed through research with the knowledge and experience gained from years of practice. 

Over the next few months a number of outputs and guidance documents will be published which have a strong geotechnical and engineering themes which may be of interest to a wider group people working in the construction industry. Most of these outputs will be standalone documents that can be used straight away by other practitioners. However, some of the projects are best seen as contributing to guidance and processes that are already under development such as the NZGS Guidelines.

Project summaries

A Risk Based Framework for Earthquake Ground Motion Hazard Estimation, New Zealand
Authors: James Dismuke and Jeff Fraser, Golder Ltd

Earthquakes cause several hazards that affect humankind and the built environment, either directly (e.g. ground shaking) or indirectly (e.g. liquefaction caused by ground shaking). Understanding earthquake the magnitude of ground shaking, or in other words, the earthquake ground motion hazard, is critical to understanding the earthquake risk for planning, design, and development in New Zealand. There are several techniques for determining ground motions for input into the planning and design of built infrastructure.  Each technique has its pros and cons, and some techniques are more suited to some projects than others. 

This report provides a framework for decision makers, policy makers, developers, owners, engineers, and others to select the level of effort (i.e. appropriate ground motion hazard analysis techniques) to suit the risk-profile of their specific projects. Detailed technical guidance about how to perform these hazard analyses is not in the scope of this report. This report comprises:

  • Definition of terms and concepts used in the report;
  • Summary of current New Zealand earth ground motion estimation guidance;
  • Methods and techniques for determining ground motions for design;
  • Risk-informed framework for determining with earthquake ground motions approach is appropriate to the situation; and
  • Answers to frequently asked questions.

Spatial correlations of underground pipeline damage with liquefaction-induced ground surface deformations and CPT-based liquefaction vulnerability index parameters
Authors: Dr Sjoerd van Ballegooy and Dr Luke Storie, Tonkin + Taylor; Dr Dimitra Bouziou, Cornell University / GEK TERNA; Prof Thomas O’Rourke, Cornell University

The Christchurch Earthquake Sequence of 2010-2011 caused extreme and widespread damage to the 3 waters pipe network of Christchurch. It is widely accepted that most of this damage was caused by liquefaction and lateral spreading. Researchers and practitioners have learnt many lessons in assessing liquefaction induced damage from these experiences. This report develops tools to assess the potential for pipeline damage based on correlations with liquefaction-induced ground movement and soil come penetration test (CPT) based liquefaction measures and indicators. The correlations and indicators can be used for pre-earthquake event estimates as well as post-event rapid triage of pipe damage. Key inputs to the assessment are a comparison between pre and post-event LiDAR surveys; satellite imagery; CPT-based assessments of liquefaction vulnerability and earthquake induced Peak Ground Velocity data (PGV).

The report explains how the data sets were collated and analysed to develop functions for pipe repair rates expressed in the number of predicted breaks per kilometre of pipeline. These repair rates cannot predict specific damage at any one location, rather they can identify areas and pipe types where damage is more likely to occur and areas where it is less likely to occur and provide an expected damage rate  for those respective areas.   Tools have been developed to facilitate this approach which can be readily applied by practitioners when responding to liquefaction induced damage.

Invasive Seismic Testing – a summary of methods and good practice
Author: Rick Wentz, Wentz-Pacific ltd

Seismic shear wave tests are routinely used in geotechnical engineering for a variety of purposes ranging from assessing static foundation settlement to estimating earthquake ground motions.  In particular, an accurate determination of soil shear wave velocity is required for robustly determining the site subsoil class when using the New Zealand seismic loadings standard NZS1170.5, as well as assessment of site-specific seismic response which is used as an input into building design.  

In the aftermath of the 2010-2011 Canterbury and 2016 Kaikoura earthquakes, seismic shear wave testing has become more commonly used in geotechnical earthquake engineering.  However, several critical aspects of both data collection and data processing are commonly not well understood by either the contractors collecting and processing the data or the geotechnical and structural engineers using the data.  This can lead to incorrect and possibly unconservative design assumptions.  

This report summarises the invasive seismic test methods typically used in New Zealand geotechnical engineering practice to measure shear and compression wave velocities.  It describes the test procedures and data processing that are generally accepted as “good practice” – i.e. the procedures and processing that are necessary to obtain accurate and representative data that can be relied upon by geotechnical engineers for analysis and design.  The report also describes the uncertainty inherent in all of the testing methods, including sources of uncertainty and how to quantify it.  An example of an assessment of uncertainty using actual field data is provided, as are recommendations for what information should be included when reporting test results. 

Guideline for Assessing Technical Resilience of Three Waters Networks – Simplified Assessment Method
Authors: Marcus Gibson, Melanie Liu and David Heiler, Beca Ltd

The guideline has been prepared, based on lessons from the Canterbury earthquake sequence, to support local authorities and the private sector (including asset managers, operators and engineers) at local and regional levels with assessing technical resilience of their three waters infrastructure and in developing strategies to improve network resilience, inform pre-event planning, and post-event emergency support and recovery.  The focus is on infrastructure placed in land potentially vulnerable to any geotechnical natural hazard. A particular example is shown in relation to liquefaction prone land – which includes many areas around New Zealand commonly near rivers, harbours and the coast.

The guideline aims to standardise the assessment of technical resilience across New Zealand and to encourage collaboration, while maintaining the ability for users to tailor the assessment approach to fit the specific requirements and needs of their community.

Rock Fall Risk Mitigation: Capturing experience from the Kaikoura and Canterbury earthquakes
Author: Rori Green, Rori Green Consulting Ltd

Landslides and rock falls that occurred as a result of the 2010/2011 Canterbury earthquakes and the 2016 Kaikoura and caused significant damage. This threatened critical transportation infrastructure particularly SH1 and the main rail corridor running down the top half of the east coast of the south Island.  Various measures were used to mitigate rockfall risk to the infrastructure and the public who utilises this infrastructure.   

Helicopter sluicing (i.e. dropping buckets of water from helicopter) was a key method used following the Kaikoura earthquake to quickly clear potentially unstable debris from slopes and allow recovery works to be undertaken more safely. It is believed that this may have been the largest sluicing project undertaken anywhere in the world.  Very little published information currently exists about sluicing. Experience has revealed sluicing was very effective in many cases and less so in others; in a few cases it may have even worsened the situation.

In addition, use of temporary rock fall protection in NZ has increased significantly as a result of recent earthquakes. In some locations, the protection has remained in place for up to 5 years. Temporary protection measures help mitigate risks to people and infrastructure during recovery works until permanent solutions can be installed.  Due to its temporary nature, and because it may be deployed rapidly in response to an event, there is often limited design input.  Rock fall impact capacity and performance is generally not well understood.  

Given there are many locations around NZ where transportation routes and other assets are situated immediately adjacent to steep slopes with rock fall hazards which could be exacerbated by either seismic activity or heavy rainfall, it is likely similar situations will happen again requiring urgent remedial action.  

This document will capture the knowledge and experience related to two separate aspects of the mitigation works:  helicopter sluicing and temporary rockfall protection works. This document will provide practical information to designers, client representatives/decision makers and project managers that can be utilised on future projects in similar situations.

Finding these resources

All of the above report are, or will shortly be available through the Quake Centre’s Resource Portal found here: https://resources.quakecentre.co.nz/

This portal also contains previous geotechnical, structural and other infrastructure related work developed by the Quake Centre over the past five years. This work has been funded by EQC and our other Industry Partners. Each project has its own industry reference group that has been involved in setting the scope and reviewing the project to ensure that it is technically accurate and meets the industry identified need.

Ongoing and future projects

Debris Flow Guideline

Work is also underway to develop a Debris Flow Guideline. It is envisaged that the final guideline is likely to cover: 

  1. Debris Flow Characteristics 
  2. A review of damaging historical debris flows and lahars in New Zealand (and elsewhere as required) 
  3. Hazard Assessment 
  4. Mitigation Design 
  5. Statutory and Regulatory Requirements 
  6. Worked Examples 

Getting involved in future projects

The Quake Centre is always interested in looking at projects that meet a clearly identified industry need, in particular those that align with EQC’s strategy of Stronger Buildings on Better Land Supported by Resilient Infrastructure. 

If you wish to be involved in ongoing or future projects please contact Greg Preston at greg.preston@canterbury.ac.nz .

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ISSN 01116851