Recent Evolution and Implementation of Geotechnical Design Practice in New Zealand

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Published 01 June 2019
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Recent Evolution and Implementation of Geotechnical Design Practice in New Zealand

ABSTRACT

Following the 2010-2011 Canterbury Earthquake Sequence a Royal Commission of inquiry provided approximately 200 recommendations to the Ministry of Business, Innovation & Employment (MBIE). Of these, over thirty were specific to geotechnical engineering. The royal inquiry recommended that MBIE work with industry to improve geotechnical engineering practice in New Zealand. In response, MBIE collaborated with the New Zealand Geotechnical Society to develop the Earthquake Geotechnical Engineering Practice Series which is commonly referred to as “The Modules”. This paper presents a discussion on the uptake of the Modules and the education program which was developed to promote consistency in everyday engineering practice. The authors also discuss the findings of an online survey and the limitations of the Modules and frustrations voiced by practitioners. The paper closes with the author’s thoughts on future guideline topics for geo-professionals and other engineering fields to improve the standard of earthquake geotechnical engineering in New Zealand.

1. Introduction

1.1 Background

At the 19th International Conference on Soil Mechanics and Geotechnical Engineering that was hosted by the ISSMGE in Seoul, 2017, Price and Stannard [immediate past chair of the New Zealand Geotechnical Society (NZGS) and ex-Chief Engineer of the Ministry of Business, Innovation and Employment (MBIE), respectively] introduced the New Zealand Earthquake Geotechnical Engineering Practice Series (The Modules) to the international community. The Modules were developed following the devastating Canterbury Earthquake Sequence (CES) events in 2010 and 2011. The Canterbury Earthquakes Royal Commission (CERC) of inquiry provided 189 recommendations to MBIE. Of these, over 30 were specific to earthquake geotechnical engineering, with CERC recommending that MBIE work with industry to improve earthquake geotechnical engineering practice in New Zealand. The Modules were developed with that recommendation and goal in mind.

1.2 Current Guidance in New Zealand

The Modules have been published as a series and released progressively; each on a different aspect of earthquake geotechnical engineering. The Modules are issued as guidance under Section 175 of the Building Act 2004 and herein referred to as Modules. Module 1 provides an overview of the Modules followed by Modules 2 and 3 that provide guidance on geotechnical investigation, identification, assessment, and mitigation of liquefaction hazards. Modules 4, 5 and 6 provide guidance on earthquake resistant foundation design, and the design of ground improvement and retaining walls. Use of the Modules took on more urgency, as the CES events were followed by the Kaikoura earthquake in November 2016 and ex-Tropical Cyclone Gita, which resulted in infrastructure damaging floods and strong winds during February 2018.

The series of Modules was produced as a collaborative partnership between the NZGS and MBIE. Principally the Modules were developed for practicing geotechnical professionals who have a sound background in soil mechanics and earthquake engineering in New Zealand. However, other engineering disciplines are using the Modules daily. The authors set out to explore the implementation of the Modules and gather more information from “users” by way of an online survey.

A full copy of all the Module documents may be downloaded from the MBIE website: https://www.building.govt.nz/building-code-compliance/geotechnical-education.

2 ONLINE SURVEY

2.1 Survey development

The authors developed an online survey, using a web-based software system, and invited members of several Technical Societies to respond. The survey was available between 28 August and 7 September 2018 and sent to members of NZGS, the New Zealand Society for Earthquake Engineering (NZSEE) and the Structural Engineering Society New Zealand (SESOC). Membership of the societies total 1245, 800 and 2100 respectively.

2.2 Survey boundaries and questions

An opening question asked if respondents agreed to their feedback to be used for this paper. Answering ‘no’ led the respondent out of the survey with an automatically generated “thank you” response.

The survey questions were grouped into four sections. Section 1 was aimed at establishing respondents’ engineering background, professional experience, engineering discipline and geographic location. Section 2 set out to gather an understanding of the respondents’ daily use of the Modules. The questions presented in Section 3 asked respondents if they had attended any of the Module training sessions and if any barriers were encountered that prevented them from attending such training. Section 4 of the online survey asked what other topics of guidance should be included in future Modules.

2.3 Sample sizes

A total of 495 people responded to the online survey over the two-week period. Response rates spiked when two reminder emails were sent out to members. Only 17 respondents did not agree to their information being used as part of this paper. An additional 95 respondents only partially completed the survey.

The authors cannot accurately provide a survey response rate, due to the limitations of how the survey was disseminated to technical society members. As such, the results of this survey are indicative to the respondents only and are not representative of the New Zealand engineering community. A total of 383 respondents filled out the survey to completion and this has provided some interesting insights into the evolution and implementation of earthquake geotechnical engineering design practice in New Zealand.

3. BACKGROUND, EXPERIENCE AND LOCATION

3.1 Engineering disciplines

In response to Question 1 of the survey, just over half identified themselves as geotechnical engineers, more than two fifths as structural engineers, and the remaining respondents as either civil engineers or ‘other’ disciplines. The respondents who identified themselves as ‘other’ were; students, engineering geologists, geotechnical drillers, geophysical scientists or coastal engineers.

Respondents were generally well distributed across New Zealand, with approximately two thirds located in the three major cities of Auckland, Wellington and Christchurch. A higher representation from larger cities is not surprising in New Zealand, as a significant number of engineers work for major consultancies that are typically based in these cities to enable them to respond to large projects. A small percentage of the respondents were based overseas in Australia, Chile, Fiji, India, Peru, UK, Mexico, Philippines and Vanuatu. Figure 1 summarises the number of respondents by engineering discipline and geographic location.

Figure 1: Summary of survey respondents’ engineering discipline and geographic location.

3.2 Work experience

Half of the respondents had between 6 to 20 years’ experience (Fig. 2). The majority (over 80%) of the respondents were in the main cities of New Zealand with the exception of engineers with between 21 to 30 years’ experience.

Approximately half of recent graduates (i.e. those with less than 2 years’ experience) use the Modules in their “everyday engineering activities”. Similarly, just over half of respondents with over 30 years of experience, use the Modules regularly.

All 24 respondents (across all six experience levels) located in Tauranga, stated that they use the Modules in their everyday engineering activities. This compares to between 62% and 76% of the time for the other five New Zealand cities where respondents were based.

The authors have considered that this question may have been interpreted by some respondents as to whether they use the Modules every day, rather than do they use the Modules in their “everyday engineering activities”, meaning their standard or routine work they complete. Nevertheless, the authors are keen to broaden the use to the Modules, particularly for those in the early stages of their career, as they are the future of the industry and it will help to foster a consistent approach across the industry for the geotechnical design of seismically resilient buildings.

Figure 2: Summary of survey respondents’ years of experience.

4. USE OF MODULES

4.1 Daily use

Question 5 sought to gain an understanding of the respondents use of the Modules in their everyday engineering activities. Over half of the respondents indicated that they use the Modules between 15% and 40% of the time. Clearly, most respondents do not use the Modules that frequently during their day.

Just under 20% of respondents rarely use the Modules while about 15% of the respondents indicated that they use the Modules between 40% and 60% of the time. The remaining 20% of respondents use the Modules 60% or more each day.

This relatively low use of the Modules may be attributed to several factors, such as; their current distribution and acceptance across the industry, limitations on practical applications, and a wide variety of fields within geotechnical earthquake engineering. The authors acknowledge that the relative use of the Modules in the respondents everyday engineering activities is low, and to increase usage and their acceptance in everyday engineering work, more active or targeted discussions around their applicability, training on their use and confirmation of technical content considered “best practice” is warranted.

4.2 Frequency of use

Of the seven Modules available to practitioners, Question 6 sought to understand how often each Module was being used by the respondents in their everyday engineering activities. Module 3 (Liquefaction Hazards) was identified as the most used by respondents who identified themselves as geotechnical engineers, followed by Module 6 (Earthquake Resistant Retaining Wall Design) and Module 4 (Earthquake Resistant Foundation Design). Conversely, respondents who identified themselves as Structural Engineers used Module 6 most often, followed by Module 4.

Frequent use of Module 3 by Geotechnical Engineers was expected, as liquefaction assessments are becoming routine and part of best practice earthquake engineering in New Zealand.

Depending on scope, objectives, structure type and stage of design, both structural and geotechnical engineers are engaged to design foundations and retaining structures. Only 14% of structural engineers who responded use Module 2 (Geotechnical Investigations for Earthquake Engineering). Module 2 provides guidance on appropriate investigations to assess the ground conditions to support the seismic design of new structures, including appropriate minimum scope and methodology for undertaking such investigations.

Structural engineers are often engaged early in a project and typically engage geotechnical engineers once concept or developed designs have been completed. This can often lead to tension between the disciplines as to the appropriate quantum of site investigation. The authors note that Module 2, specifically, needs further dissemination amongst engineering professionals who are involved in earthquake engineering to promote consistency in geotechnical investigation applications and expectations.

5. MODULES ADOPTION

5.1 Barriers to use

A third of the respondents stated they do not use the Modules in their everyday engineering activities. Of these respondents, approximately 65% were structural engineering professionals, two fifths were geotechnical engineers and the remaining civil engineers or other professionals. The main barrier identified was that the guidance currently offered in the Modules is not relevant to the work they do on a daily basis. Training availability was identified as the second largest barrier to Module use.

Geotechnical engineers made up 27 out of the 129 respondents who answered ‘no’ to this question, with 12 indicating that the guidance was not relevant to their work. Figure 3 summarises the reported barriers to Module use in everyday engineering activities.

The last question within Section 2 asked if more detailed worked examples were provided to help the user understand the content, would their usage of the Modules increase? Just under three quarters of the respondents (274 out of 383) answered ‘yes’.

Figure 3: Barriers identified in using the Modules by engineering discipline.

5.2 Training

MBIE, NZGS and Engineering New Zealand (ENZ) are collaborating and working closely to deliver ongoing training to the wider New Zealand industry in the content and use of the Modules. This is being completed via a combination of traditional “classroom-based” and online forums. The currently-available online training courses can be accessed through the MBIE website.

Training on the use of the Modules has been developed and made available to all members of ENZ via their website and fortnightly email notification process. Technical societies send out additional reminder emails to their members, if appropriate, to assist in advising their members of the upcoming training opportunities.

Classroom training on Module 3 was rolled out between 19 and 28 September 2016, and 28 August and 8 September 2017 in Auckland, Christchurch, Wellington and Dunedin. Similar face-to-face training on Module 4 was presented between 7 and 21 March 2017 and 11 to 31 July 2018 in Auckland, Christchurch, Wellington, Nelson, Hamilton and Invercargill.

One quarter of respondents have attended one of the training sessions. Figure 4 below provides a breakdown of the responses to Question 9 by discipline type.

Figure 4: Number of participants who have attended specific training on the use of the Modules.

The authors note that training on the use of Module 6, at the time the survey was completed, had not been released. It is assumed, that respondents who indicated that they had attended Module 6 training, are likely to have attended the Retaining Wall Design Practice, which is recommended prerequisite training for engineers attending the Module 6 training course.

The survey results indicate that the Module 4 training courses have had most attendance followed by Module 3, with 59 and 48 respondents attending these sessions, respectively. Conversely, attendance data collected by ENZ indicates that they have had 306 and 138 people attend training sessions on Module 4 and 3, respectively.

The cost of face-to-face training sessions was identified as the second biggest barrier to respondents attending the training, followed by the respondents either being unavailable to attend the training (due to work commitments), or not being aware such training was available. The authors were expecting to see a high return rate of respondents being ‘too busy’ to attend the training, however, this was not the case (refer to Fig. 5). There is a desire for engineers to attend the Module training sessions, however there are several other barriers.

Of the respondents who indicated that the training was not beneficial to their needs, this was summarised as generally being too high level or too simplified; or, that most geotechnical practitioners should be able to understand and apply the technical content by self-reading and on-the-job learning. Such geotechnical practitioners also identified that a lot of training content was ‘routine’ to them and not additional learning benefit.

Figure 5: Barriers identified to attending the Module face-to-face training.

6. FUTURE GEOTECHNICAL MODULES

6.1 Survey responses

The final section of the online survey gathered respondents’ thoughts on what other aspects of earthquake geotechnical engineering, or geotechnical engineering in general, should be the focus of future Modules. The survey included two options or a free field text box. The two options offered (a) slope stability of soil and rock slopes, and (b) soft soils.

Of the 383-people surveyed, 76% responded that they saw value in the development of a new slope stability of soil and rock slopes module, closely followed by 64% responding that a soft soil module should also be developed. A wide variety of fields within geotechnical engineering were presented as other options to focus on, including:

– Soil and rock anchor design for seismic strengthening projects
– Foundation design in expansive soils
– Ground Motion Prediction Equations (GMPE)/ Probabilistic Seismic Hazard Assessments (PSHA) and Site Response assessments
– The use of, interpretation, and appropriateness of hand tool investigations, using Scala Penetrometers, Shear Vanes and Hand Augers
– Soil-Structure-Interaction (SSI) and improved collaboration procedures between Structural and Geotechnical Engineers
– Working with, and designing in, volcanic and pumice soils.

The above responses indicate that a broad range of guidance is sought from the engineering community to assist in their everyday engineering activities and to improve the standard of earthquake geotechnical engineering practice in New Zealand.

6.2 Maintenance and updating of modules

The authors believe that ongoing review and update of the Modules is required to ensure that they remain relevant and a reflection of current best practice. MBIE and the NZGS are working together with ENZ to develop a sustainable long-term review program.

The final review programme (which was still being finalised at the time of writing this paper) will aim to ensure that all Modules are reviewed in a logical and timely manner. At this stage, it is envisioned that one to two documents will be reviewed each year, with a review of the entire suite being completed every five to seven years.

6.3 CPD

Continuing Professional Development (CPD) is a key component of the Chartered Professional Engineer (CPEng) system in New Zealand. All holders of the CPEng quality mark have “an ongoing requirement to undertake education, maintain a current knowledge base and improve skills and knowledge”. It is expected, that all CPEng holders complete no less than 40 hours of CPD activities per annum. It is generally expected, that all New Zealand CPEng holders who specialise in the field of geotechnical engineering become familiar with the Modules.

6.4 Future modules

The NZGS plans to continue working collaboratively with MBIE and ENZ and the wider industry to develop four or five additional geotechnical design modules. Planning by the NZGS to develop geotechnical design Modules for slope stability, ground anchors and soil nails, and subsoil drainage has commenced. It is also envisaged, that the scope of the additional documents will be expanded, as appropriate, to include non-seismic design situations.

7. DISCUSSION

While the Modules are clearly a useful set of “tools” for practicing engineers in New Zealand; their use has not been universally or consistently adopted. Better adoption of the Modules, may improve with time, particularly as university study and graduate training programmes start to raise awareness and promote the use of the Modules with their students.

For those considering development of guidelines, the authors would recommend interactions with engineering practitioners are made early in the process. Such interactions could include pre-development surveys to understand the needs and requirements of practitioners. A well-planned and appropriately-targeted training programme should also be developed in conjunction with, and released in parallel with, the Modules.

Finally, the authors have observed that the Modules have resulted in some registrational ambiguity, as while they have been disseminated as guidelines, some users consider them to be Standards. At the NZGS Symposium 2017 in Napier, there was lively debate on whether the Modules should be further developed into NZ Standards. The authors believe the Modules should remain as guidelines, with the understanding that they are regularly updated to reflect International and New Zealand best practice. Standards are typically updated infrequently, after much debate and invariably with compromises.

8. ACKNOWLEDGEMENTS

The authors would like to acknowledge the many practitioners who responded to our survey and those that have contributed to the development of the Modules. Ella Priest Forsyth of Beca kindly developed and ran the online SurveyGizmo, thank you. Engineering New Zealand kindly provided the data on the training sessions. The authors would also like to thank the NZGS, SESOC and NZSEE for allowing the survey to be disseminated to their members, and Rachael Scott-Schumacher for her excel and data analytics skills.

9. REFERENCES

  • Price, C.H. & Stannard, M. 2017. The development of Modules and continuing professional development in earthquake geotechnical engineering design practice in New Zealand. Proc. of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul.

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