New Zealand Geotechnical Society Research Scholarship Reports

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Published 10 July 2020
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New Zealand Geotechnical Society Research Scholarship Reports

The NZGS Management Committee provides funding for a scholarship that would enable a member of the Society to undertake postgraduate research in New Zealand that would advance the objectives of the Society. Through this scholarship, the Society hopes to encourage members to enrol for post-graduate research (e.g., PhD, Masters by research) or undertake independent research (e.g., post-doctoral research) that would not otherwise be possible for them.

The fields of research are expected be in Engineering Geology and/or Geotechnical Engineering. The scholarship will be next awarded in 2020. Submissions are due 31 October 2020. Check the website for further information.

The following reports are provided by the two most recent recipients of Scholarships:

NZGS Research Scholarship 2019 Progress Report

Doug Mason

I received the NZGS Research Scholarship in April 2019, to contribute towards my PhD research at the University of Canterbury in 2019 and 2020. This report summarises the research covered under the scholarship, the work completed in 2019 and the work planned for 2020.

The aim of my PhD research is to investigate earthquake-induced landsliding and its impacts on infrastructure, to help inform the future design of slopes and management of landslide hazards. Drawing lessons from the performance of slopes in past earthquakes is invaluable to gain this understanding. The impetus for this research is to learn from the damage and disruption to infrastructure caused by the 2016 Kaikura earthquake, and to document the key lessons for future practice.

The NZGS Scholarship funding has enabled me to carry out additional independent research into landsliding in past (i.e. pre-
Kaikura) earthquakes in New Zealand, that would not otherwise have been achievable. This will help broaden the understanding of earthquake induced landsliding beyond the Kaikura research and help ensure that the eventual lessons and recommendations draw on a wider cross section of data from different parts of the country.

The scholarship funding provided by the Society was split into two parts: funding for the first year in 2019 to go towards documenting and investigating earthquake-induced landsliding in pre-Kaikura earthquakes, and the remainder for 2020 to go towards analysis of selected slope failures. The 2019 scholarship has provided funding for travel, fieldwork expenses and consumables, as well as to support my taking time away from work to dedicate to the study.

Part 1 – Collate records of earthquake-induced landsliding

The objective of this step was to identify parts of the country that are subject to high seismicity and that are likely to have significant cut slopes, and to select several study areas that have experienced strong ground shaking in historical earthquakes and that have contrasting geological materials and terrain to the Kaikoura area. Hancox et al. (1997) compiled landslide records for historical earthquakes in New Zealand, which provided the basis for selecting a shortlist of study areas and earthquake events for this research, as described below. From these study areas, I have collated records of where slope failures have occurred along transport routes or other infrastructure corridors.  This has been based on a literature review of available information including geological maps, research papers, aerial photographs, and reconnaissance reports, first-hand accounts and photographs from the time of the event.

Wairarapa

The eastern part of Wairarapa, away from the axial ranges of the central North Island, consists of rolling to steep hill country underlain by Tertiary sedimentary rocks (mudstones, sandstones and limestones). This area experienced strong ground shaking in several key historical earthquakes. The MW 8.2 Wairarapa earthquake in 1855 caused widespread landsliding over the southern North Island and upper South Island. Intense landsliding was triggered in the Wairarapa hills, and rock slides and rock falls caused extensive damage to roads and tracks, as well as in the Hutt Valley and Wellington. Because of the age of this earthquake, historical records with accurate locations of the landsliding are scarce. The MW 7.2 and MW 6.8 Masterton (Wairarapa) earthquakes of 1942 also caused extensive landsliding in the Tertiary rocks in hill country to the east of Masterton. Most roads to the east and south of Masterton were blocked by landslides, particularly from failure of cut slopes. The Main Trunk Line railway south of Plimmerton was blocked by a landslide and small rock falls were reported along State Highway 2 in the western Hutt Valley.

Buller

The area around the Buller River between Murchison and Westport consists of steep forested hills and mountains with deeply incised river valleys, underlain by Paleozoic greywacke, Mesozoic granite, and Tertiary sedimentary rocks (principally limestone, sandstone and calcareous mudstone). This area has been subjected to strong ground shaking in the 1929 MS 7.8 Murchison earthquake and the 1968 MW 7.1 Inangahua earthquake. These events triggered widespread landsliding, including extensive and severe damage to roads, rail, houses and other infrastructure. For example, the Buller Gorge road between Murchison and Inangahua was closed by landslides and rock falls for 22 months following the Murchison earthquake.

Arthur’s Pass

The Arthur’s Pass area in the Southern Alps is characterised by steep mountainous terrain with deeply incised river valleys, underlain by Paleozoic to Mesozoic greywacke bedrock. This area has been subjected to several large historical earthquakes (all named after Arthur’s Pass); a MS 7.1 earthquake in 1929, a MW 6.7 earthquake in 1994, and a ML 5.5 earthquake in 1995. All of these events caused significant landsliding and consequential damage and disruption to Arthur’s Pass township, State Highway 73 and the West Coast rail line.

Christchurch Port Hills

The Port Hills consist of rolling to steep hills with long narrow ridges and steep bluffs and cliffs, underlain by Tertiary volcanic rocks and Quaternary loess soils. The 2010-2011 Canterbury earthquake sequence caused widespread landsliding and slope deformation over the Port Hills. Rock falls and cliff collapses damaged hundreds of houses and caused four fatalities, as well as closing local arterial roads across the Port Hills between Christchurch and Lyttelton.

Part 2 – Document characteristics of slope failures

The objective of this second phase of work was to identify key sites for further investigation and to document the characteristics of the failures at those sites. Potential sites (or sections of road corridor) for investigation were identified from the historical information gathered in the desk study. These were inspected in reconnaissance visits to Christchurch, Arthur’s Pass, and Buller to observe the current condition of the slopes and better understand the geology and the geometry of the failure sites, and to help determine the failure mechanisms and extent of impacts on the road corridors.

An inventory of landslides along key road corridors impacted by past earthquake-induced landslides has been developed based on the information gathered in the desk study and supplemented by the observations made during the reconnaissance inspections. The landslides are being captured in GIS, including attribute information such as the material type, landslide type, availability of information/level of confidence in the mapping, and the approximate extent of landslide debris. The inventory will be added to and refined as further information becomes available from ongoing literature reviews, aerial photograph mapping and site visits as the research progresses.

A second objective of this part of the research was to identify where cut slopes have been formed, to compare the locations of landslides with the extent of modified slopes. The locations and extents of cut slopes are not able to be mapped systematically along the earthquake-affected corridors without detailed topographic information such as LiDAR, however photos dating from the time of the earthquake as well as recent corridor imagery (e.g. Waka Kotahi / NZ Transport Agency corridor video and Google Streetview) have allowed the identification of cut slopes at particular sites, although the slope heights and angles of the cuts at the time of the earthquake in that location cannot reliably be determined.

Upcoming work

The work scheduled for 2019 has largely been completed, apart from the GIS mapping of landslides which will be completed by the end of April. The work planned under the scholarship in 2020 consists of back-analysing selected landslide sites to better understand the mechanisms of failure and to help identify important factors that contributed to the observed behaviour. The desk study in part 1 included searching for detailed topographic data (e.g. LiDAR) to assist in the identification and mapping of landslides and to provide ground surface information for the slope analysis. Unfortunately there is currently no LiDAR data available for areas such as Arthur’s Pass and Buller Gorge, and therefore to fill this gap I will survey key sites in these areas with an Unmanned Aerial Vehicle (UAV) or Terrestrial Laser Scanner (TLS) to provide high resolution images and 3D ground surface models of the slopes. Given the current restrictions on travel due to the Covid-19 emergency, this surveying work will be carried out once the restrictions are lifted. The slope analysis will be carried out afterwards, likely to be in the second half of this year.

References

Hancox, G.T., Perrin, N.D., Dellow, G.D. (1997). Earthquake-induced landsliding in New Zealand and implications for MM intensity and seismic hazard assessment. GNS Science client report 43601B. 85 p.

 

NZGS Research Scholarship Progress Report

Heba Elsaidy (PhD student, University of Auckland)

The New Zealand Geotechnical Society (NZGS) scholarship is to acknowledge the contribution of post-graduate students across the universities in New Zealand to the profession and to the society. The recipient is selected by a committee mainly composed of industry practice leads in well-known engineering companies in the New Zealand region. Being one of the recipients of this respected scholarship, it is interesting to share my experience regarding how NZGS scholarship was able to assist my PhD research as well as future goals. It should be mentioned that I got the NZGS scholarship for the last year of my PhD studies.

On research, one of the main outputs of a research scholarship is contribution to existing knowledge by doing innovative research. The primary aim of my research is to have a better understanding of the hydro-mechanical behavior of unsaturated expansive soils behind retaining structures. The main outputs and/or phases of the current research are summarized as follows: (1) Two universal empirical formulas were developed to predict the swelling pressure and strain using simple input parameters; (2) An advanced 3D scanning technique using structured light, which was developed to obtain the shrinkage curve and Soil-water characteristic curve (SWCC); and (3) The modified K0 triaxial apparatus, which is able to capture the 3D response of compacted expansive soils subjected to multiple wetting and drying cycles. This information is useful to geotechnical practitioners to simulate and investigate true field conditions in the laboratory.

Figure 1 A typical K0 CV triaxial swelling/shrinkage test including vertical and lateral swelling pressures versus time

Some of the results obtained from phase 3, which was achieved after receiving NZGS scholarship could be summarised as follows:

(1) A modified suction-controlled K0 triaxial apparatus was developed and capable to assess the effect of wetting and drying cycles on the swelling/shrinkage pressure change for unsaturated soil testing; (2) Due to the nature of expansive soils, a complicated swelling/shrinkage behaviour in addition to hydraulic hysteresis during wetting-drying cycles was observed; and (3) Four wetting and drying cycles are needed to reach equilibrium swell/shrink pressure after wetting. Figure 1 shows a typical K0 CV triaxial swelling/shrinkage test, which comprises of isotropic compression (IS) followed by a series of constant volume selling/shrinkage cycles under K0 condition. As anticipated, this figure shows that that both vertical and lateral swelling pressure increased with time during wetting and decreased during drying. In addition, determination of swelling anisotropy is achieved by the synchronized measurement of the swelling pressures in both vertical and lateral direction on the same soil specimen using the modified suction-controlled K0 triaxial apparatus in Geomechanics lab. at the University of Auckland.

Most post-graduate students struggle financially, especially with paying tuition fees. This scholarship allowed me to follow my dreams by boosting my academic goals and breaking a big financial barrier.

In addition, this scholarship improved my performance during my PhD journey. I was working in my last phase in my PhD studies and needed to focus more on improving my knowledge and skills. Thus, this scholarship gave me extra time to study by taking away some of my financial concerns.

Previous successful PhD candidates keep advising us (current PhD students) to decide a future career path. As an international student, this remained one of my biggest concerns. A career advantage can be obtained by listing this competitive scholarship on my resume. Moreover, as previously mentioned, the scholarship committee is composed of leaders in well-known engineering companies across New Zealand. Hence, it gives access to increase networking which is highly required in achieving my future career goals.

The scholarship means the hard work has really paid off. This scholarship offered by NZGS is a great honour for me. It is not just receiving financial help; it has given me the potential to achieve more for society. The scholarship gave me motivation and confidence during various interviews. Now, I am working in an international engineering company as a geotechnical engineer.

Lastly, I would like to express my sincere appreciation to my main supervisors, Prof. Michael J. Pender and Dr. Ryan Yan from the University of Auckland; it is a pleasure of being one of their students too. Earnest gratitude is due to my daughter for her patience and taking her own responsibility during the past four years. Last but not least appreciation goes to the NZGS committee for providing valuable comments to help my research.

 

 

 

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ISSN 0111-6851