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Research papers, University of Canterbury Library

Despite their good performance in terms of their design objectives, many modern code-prescriptive buildings built in Christchurch, New Zealand had to be razed after the 2010-2011 Canterbury earthquakes because repairs were deemed too costly due to widespread sacrificial damage. Clearly a more effective design paradigm is needed to create more resilient structures. Rocking, post-tensioned connections with supplemental energy dissipation can contribute to a damage avoidance designs (DAD). However, few have achieved all three key design objectives of damage-resistant rocking, inherent recentering ability, and repeatable, damage-free energy dissipation for all cycles, which together offer a response which is independent of loading history. Results of experimental tests are presented for a near full-scale rocking beam-column sub-assemblage. A matrix of test results is presented for the system under varying levels of posttensioning, with and without supplemental dampers. Importantly, this parametric study delineates each contribution to response. Practical limitations on posttensioning are identified: a minimum to ensure static structural re-centering, and a maximum to ensure deformability without threadbar yielding. Good agreement between a mechanistic model and experimental results over all parameters and inputs indicates the model is robust and accurate for design. The overall results indicate that it is possible to create a DAD connection where the non-linear force-deformation response is loading history independent and repeatable over numerous loading cycles, without damage, creating the opportunity for the design and implementation of highly resilient structures.

Research papers, University of Canterbury Library

With the occurrence of natural disasters on the increase, major cities around the world face the potential of complete loss of infrastructure due to design guidelines that do not consider resilience in the design. With the February 22nd, 2011 earthquake in Christchurch, being the largest insured event, lessons learnt from the rebuild will be vital for the preparation of future disasters. Therefore the objective of this research is to understand the financial implications of the changes to the waste water design guidelines used throughout the five year rebuild programme of works. The research includes a study of the SCIRT alliance model selected for the delivery that is flexible enough to handle changes in the design with minimal impact on the direct cost of the rebuild works. The study further includes the analysis and compares the impact of the three different guidelines on maintenance and replacement cost over the waste water pipe asset life. The research concludes that with the varying ground conditions in Christchurch and also the wide variety of materials in use in the waste water network up to the start of the CES, the rebuild was not a ‘one size fits all’ approach.

Research Papers, Lincoln University

Purpose - The purpose of this paper is to identify through the application of Actor Network Theory (ANT) the issues and impediments to the implementation of mandatory seismic retrofitting policies proposed by the New Zealand Government. In particular the tension between the heritage protection objectives contained in the Resource Management Act 1991 and the earthquake mitigation measures contained in the Building Act 2004 are examined. Design/methodology/approach - The paper uses a case study approach based on the Harcourts Building in Wellington New Zealand and the case law relating to attempts to demolish this particular building. Use is made of ANT as a 'lens' to identify and study the controversies around mandatory seismic retrofitting of heritage buildings. The concept of translation is used to draw network diagrams.

Research papers, The University of Auckland Library

Eccentrically Braced Frames (EBFs) are a widely used seismic resisting structural steel system. Since their inception in the late 1970s, they have been a viable option with an available stiffness that is between simple braced systems and moment resisting systems. A similar concept, the linked column frame (LCF), uses shear links between two closely spaced columns. In both cases, the key component is the active link or the shear link, and this component is the objective of this study. The performance of high rise EBF buildings in the 2010 and 2011 Christchurch earthquakes was beyond that which was expected, especially considering the very high accelerations recorded. As the concrete high-rises were torn down, two EBF buildings remained standing and only required some structural repair. These events prompted a renewed interest in bolted shear links, as well as their performance. While some research into replaceable shear links had already been done (Mansour, 2011), the objectives of this study were to improve on the shear link itself, with the consideration that links built in the future are likely to be bolted. The main components of this study were to: 1. Reduce or eliminate the requirements for intermediate web stiffeners, as they were suspected of being detrimental to performance. Furthermore, any reduction in stiffening requirements is a direct fabrication cost saving. Links with low web aspect ratios were found to achieve exceptional ductilities when no stiffeners were included, prompting new design equations. 2. Ensure that the stresses in the ends of links are adequately transferred into the endplates without causing fractures. Although most of the experimental links had web doubler plates included, four had varied lengths of such doubler plates from 0.0 in. to 8.0 in. The link without any doubler plates performed to a similar level to its peers, and thus it is likely that links with quality end details may not need web doubler plates at all. 3. Evaluate the performance of a link with double sided stiffeners without the use of web welds, as opposed to conventional single sided, welded stiffeners. This link performed well, and web-weld-less double sided stiffeners may be an economical alternative to conventional stiffeners for deeper sections of links. 4. Evaluate the performance of a link with thin endplates that are made efficient with the use of gusset plates. This link performed to an acceptable level and provides evidence for a cost effective alternative to thick endplates, especially considering the high overstrength end moments in links, typically requiring 16-bolt connections. 5. Examine the potential use of an alternative EBF arrangement where the collector beam is over sized, and the link section is formed by cutting out parts of the beam's web. After running a series of finite element models each with a unique variation, a number of approximate design rules were derived such that future research could develop this idea further experimentally. 6. Ensure that during testing, the secondary elements (members that are not the shear link), do not yield and are not close to yielding. None of the instrumented elements experienced any unexpected yielding, however the concerns for high stresses in the collector beam panel zone during design were warranted. The use of an existing New Zealand design equation is recommended as an extra check for design codes worldwide. The above objectives were mainly conducted experimentally, except: the data set for item 1 was greatly expanded through the use of a calibrated numerical model which was then used in an extensive parametric study; item 5 was purely finite element based; and, a small parametric study was included for item 3 in an attempt to expand on the trends found there.

Research papers, The University of Auckland Library

Following the 2010/2011 Canterbury earthquakes the seismic design of buildings with precast concrete panels has received significant attention. Although this form of construction generally performed adequately in Christchurch, there were a considerable number of precast concrete panel connection failures. This observation prompted a review of more than 4700 panel details from 108 buildings to establish representative details used in both existing and new multi-storey and low rise industrial precast concrete buildings in three major New Zealand cities of Auckland, Wellington and Christchurch. Details were collected from precast manufacturers and city councils and were categorised according to type. The detailing and quantity of each reviewed connection type in the sampled data is reported, and advantages and potential deficiencies of each connection type are discussed. The results of this survey provide a better understanding of the relative prevalence of common detailing used in precast concrete panels and guidance for the design of future experimental studies. http://www.nzsee.org.nz/publications/nzsee-quarterly-bulletin/

Research papers, Victoria University of Wellington

Diverse Density proposes an alternative housing strategy to the idealistic top-down process of housing development.  The term ‘Top – down’ refers to a situation in which decisions are made by a few people in authority rather than by the people who are affected by the decisions (Cambridge).  Problems/Position/Question: New Zealand’s urban housing is in a period of flux. Pressures of densification have permitted the intervention of medium density housing development schemes but these are not always successful. These typically top-down processes often result in internally focused design schemes that do not adhere to their specific context. The subsequent design outcomes can cause detrimental impacts to the local, urban and architectural conditions.  With vast quantities of council regulations, building restrictions and design guidelines clouding over the housing sector, commonly referred to as ‘red tape’, occupant participation in the housing development sector is dwindling. A boundless separation between top-down and traditional housing processes has occurred and our existing neighbourhoods and historic architectural character are taking on the brunt of the problem. The thought-provoking, alternative housings strategies of key research theorists Alejandro Aravena and John Habraken frame positions that challenge contemporary densification methods with an alternative strategy.  This position is addressed by endeavoring to answer; How can demands for denser housing achieve dynamic design responses that adhere to changes in occupancy, function and local site conditions?  Aim: The aim of this thesis is to challenge New Zealand’s current housing densification methods by proposing an alternative densification strategy. Explicit devotion will be attributed to opposing top-down building developments. Secondly, this thesis aims to test a speculative site-specific housing model. The implementation of a Christchurch housing scenario will situate an investigative study to test the strategy and its ability to stimulate greater diversity, site responsiveness, functional adaptability and occupancy permutation. The post-earthquake housing conditions of Christchurch provide an appropriate scenario to test and implement design-led investigations.  Objectives: The primary objectives of this design-led research investigation it to challenge the idealistic top-down method of developing density with a new method to:  - Develop contextual architectural cohesion - Encourage residential diversity - Reinvigorate architectural autonomy - Respond to, and recognise, existing site conditions - Develop a housing model that: - Adapts to occupant functionality preferences - Caters to occupancy diversity - Achieves contextual responsiveness  The proposition is addressed through a speculative design-led scenario study. A well-established Christchurch urban environment is adopted to implement and critique the envisioned alternative strategy. Development of the designs responsiveness, adaptability, and functionality produce a prototype housing model that actively adheres to its particular context.  Implication: The implications of this research would be an alternative densification strategy to perceive the advancement of punctual assessment of building compliance. With accelerated building processes, the research may have implications for addressing New Zealand’s housing crisis whilst simultaneously providing diverse, personable and responsive architectural solutions. A more dynamic, up-to-date and responsive housing development sector would be informed.

Research Papers, Lincoln University

Creative temporary or transitional use of vacant urban open spaces is seldom foreseen in traditional urban planning and has historically been linked to economic or political disturbances. Christchurch, like most cities, has had a relatively small stock of vacant spaces throughout much of its history. This changed dramatically after an earthquake and several damaging aftershocks hit the city in 2010 and 2011; temporary uses emerged on post-earthquake sites that ran parallel to the “official” rebuild discourse and programmes of action. The paper examines a post-earthquake transitional community-initiated open space (CIOS) in central Christchurch. CIOS have been established by local community groups as bottom-up initiatives relying on financial sponsorship, agreements with local landowners who leave their land for temporary projects until they are ready to redevelop, and volunteers who build and maintain the spaces. The paper discusses bottom-up governance approaches in depth in a single temporary post-earthquake community garden project using the concepts of community resilience and social capital. The study analyses and highlights the evolution and actions of the facilitating community organisation (Greening the Rubble) and the impact of this on the project. It discusses key actors’ motivations and values, perceived benefits and challenges, and their current involvement with the garden. The paper concludes with observations and recommendations about the initiation of such projects and the challenges for those wishing to study ephemeral social recovery phenomena.

Research papers, University of Canterbury Library

Liquefaction-induced lateral spreading during earthquakes poses a significant hazard to the built environment, as observed in Christchurch during the 2010 to 2011 Canterbury Earthquake Sequence (CES). It is critical that geotechnical earthquake engineers are able to adequately predict both the spatial extent of lateral spreads and magnitudes of associated ground movements for design purposes. Published empirical and semi-empirical models for predicting lateral spread displacements have been shown to vary by a factor of <0.5 to >2 from those measured in parts of Christchurch during CES. Comprehensive post- CES lateral spreading studies have clearly indicated that the spatial distribution of the horizontal displacements and extent of lateral spreading along the Avon River in eastern Christchurch were strongly influenced by geologic, stratigraphic and topographic features.

Research papers, University of Canterbury Library

This thesis studies the behaviour of diaphragms in multi-storey timber buildings by providing methods for the estimation of the diaphragm force demand, developing an Equivalent Truss Method for the analysis of timber diaphragms, and experimentally investigating the effects of displacement incompatibilities between the diaphragm and the lateral load resisting system and developing methods for their mitigation. The need to better understand the behaviour of diaphragms in timber buildings was highlighted by the recent 2010-2011 Canterbury Earthquake series, where a number of diaphragms in traditional concrete buildings performed poorly, compromising the lateral load resistance of the structure. Although shortcomings in the estimation of force demand, and in the analysis and design of concrete floor diaphragms have already been partially addressed by other researchers, the behaviour of diaphragms in modern multi-storey timber buildings in general, and in low damage Pres-Lam buildings (consisting of post-tensioned timber members) in particular is still unknown. The recent demand of mid-rise commercial timber buildings of ten storeys and beyond has further highlighted the lack of appropriate methods to analyse timber diaphragms with irregular floor geometries and large spans made of both light timber framing and massive timber panels. Due to the lower stiffness of timber lateral load resisting systems, compared with traditional construction materials, and the addition of in-plane flexible diaphragms, the effect of higher modes on the global dynamic behaviour of a structure becomes more critical. The results from a parametric non-linear time-history analysis on a series of timber frame and wall structures showed increased storey shear and moment demands even for four storey structures when compared to simplistic equivalent static analysis. This effect could successfully be predicted with methods available in literature. The presence of diaphragm flexibility increased diaphragm inter-storey drifts and the peak diaphragm demand in stiff wall structures, but had less influence on the storey shears and moments. Diaphragm force demands proved to be significantly higher than the forces derived from equivalent static analysis, leading to potentially unsafe designs. It is suggested to design all diaphragms for the same peak demand; a simplified approach to estimate these diaphragm forces is proposed for both frame and wall structures. Modern architecture often requires complex floor geometries with long spans leading to stress concentrations, high force demands and potentially large deformations in the diaphragms. There is a lack of guidance and regulation regarding the analysis and design of timber diaphragms and a practical alternative to the simplistic equivalent deep beam analysis or costly finite element modelling is required. An Equivalent Truss Method for the analysis of both light timber framed and massive timber diaphragms is proposed, based on analytical formulations and verified against finite element models. With this method the panel unit shear forces (shear flow) and therefore the fastener demand, chord forces and reaction forces can be evaluated. Because the panel stiffness and fastener stiffness are accounted for, diaphragm deflection, torsional effects and transfer forces can also be assessed. The proposed analysis method is intuitive and can be used with basic analysis software. If required, it can easily be adapted for the use with diaphragms working in the non-linear range. Damage to floor diaphragms resulting from displacement incompatibilities due to frame elongation or out-of plane deformation of walls can compromise the transfer of inertial forces to the lateral load resisting system as well as the stability of other structural elements. Two post-tensioned timber frame structures under quasi-static cyclic and dynamic load, respectively, were tested with different diaphragm panel layouts and connections investigating their ability to accommodate frame elongations. Additionally, a post-tensioned timber wall was loaded under horizontal cyclic loads through two pairs of collector beams. Several different connection details between the wall and the beams were tested, and no damage to the collector beams or connections was observed in any of the tests. To evaluate the increased strength and stiffness due to the wall-beam interaction an analytical procedure is presented. Finally, a timber staircase core was tested under bi-directional loading. Different connection details were used to study the effect of displacement incompatibilities between the orthogonal collector beams. These experiments showed that floor damage due to displacement incompatibilities can be prevented, even with high levels of lateral drift, by the flexibility of well-designed connections and the flexibility of the timber elements. It can be concluded that the flexibility of timber members and the flexibility of their connections play a major role in the behaviour of timber buildings in general and of diaphragms specifically under seismic loads. The increased flexibility enhances higher mode effects and alters the diaphragm force demand. Simple methods are provided to account for this effect on the storey shear, moment and drift demands as well as the diaphragm force demands. The analysis of light timber framing and massive timber diaphragms can be successfully analysed with an Equivalent Truss Method, which is calibrated by accounting for the panel shear and fastener stiffnesses. Finally, displacement incompatibilities in frame and wall structures can be accommodated by the flexibilities of the diaphragm panels and relative connections. A design recommendations chapter summarizes all findings and allows a designer to estimate diaphragm forces, to analyse the force path in timber diaphragms and to detail the connections to allow for displacement incompatibilities in multi-storey timber buildings.

Research papers, The University of Auckland Library

Five years after the devastating series of earthquakes in Christchurch, New Zealand, the structural engineering community is now focussing on low damage design by either proactively reducing the possibility of significant damage to primary steel members (i.e. developing seismic resisting systems that will deliver a high damage threshold in severe earthquakes) or by improved detailing of the primary steel members for rapid replacement. This paper presents a development of Eccentrically Braced Frames (EBFs) with replaceable active links. It uses the bolted flange- and web splicing concept to connect the active link to the collector beam or column. Finite element analyses have been performed to investigate the behaviour and reliability of EBFs with this new type replaceable active link. The results show a stable hysteretic behaviour and more significantly easier replacement of the damaged active link in comparison with conventional EBFs.

Research papers, University of Canterbury Library

The 2010-2011 Canterbury earthquake sequence, and the resulting extensive data sets on damaged buildings that have been collected, provide a unique opportunity to exercise and evaluate previously published seismic performance assessment procedures. This poster provides an overview of the authors’ methodology to perform evaluations with two such assessment procedures, namely the P-58 guidelines and the REDi Rating System. P-58, produced by the Federal Emergency Management Agency (FEMA) in the United States, aims to facilitate risk assessment and decision-making by quantifying earthquake ground shaking, structural demands, component damage and resulting consequences in a logical framework. The REDi framework, developed by the engineering firm ARUP, aids stakeholders in implementing resilience-based earthquake design. Preliminary results from the evaluations are presented. These have the potential to provide insights on the ability of the assessment procedures to predict impacts using “real-world” data. However, further work remains to critically analyse these results and to broaden the scope of buildings studied and of impacts predicted.

Research papers, Victoria University of Wellington

This project looks at how destroyed architecture, although physically lost, fundamentally continues to exist within human memories as a non-physical entity. The site chosen is Avonside Girls’ High School in Christchurch, New Zealand, a school heavily damaged during the February 22nd earthquake in 2011. The project focuses on the Main Block, a 1930s masonry building which had always been a symbol for the school and its alumni.  The key theories relevant to this are studies on non-material architecture and memory as these subjects investigate the relationship between conceptual idea and the triggering of it. This research aims to study how to fortify a thought-based architecture against neglect, similar to the retrofitting of physical structures.  In doing so, the importance of the emotive realm of architecture and the idea behind a building (as opposed to the built component itself) is further validated, promoting more broadminded stances regarding the significance of the idea over the object. A new method for disaster recovery and addressing trauma from lost architecture is also acquired. Factors regarding advanced structural systems and programmes are not covered within the scope of this research because the project instead explores issues regarding the boundaries between the immaterial and material.  The project methodology involves communicating a narrative derived from the memories alumni and staff members have of the old school block. The approach for portraying the narrative is based on a list of strategies obtained from case studies.  The final product of the research is a new design for the high school, conveyed through a set of atmospheric drawings that cross-examines the boundaries between the physical and non-physical realms by representing the version of the school that exists solely within memories.

Research papers, University of Canterbury Library

Social media have changed disaster response and recovery in the way people inform themselves, provide community support and make sense of unfolding and past events online. During the Canterbury earthquakes of 2010 and 2011 social media platforms such as Facebook and Twitter became part of the story of the quakes in the region, as well as a basis for ongoing public engagement during the rebuild efforts in Christchurch. While a variety of research has been conducted on the use of social media in disaster situations (Bruns & Burgess, 2012; Potts, Seitzinger, Jones, & Harrison, 2011; Shklovski, Palen, & Sutton, 2008), studies about their uses in long-term disaster recovery and across different platforms are underrepresented. This research analyses networked practices of sensemaking around the Canterbury earthquakes over the course of disaster response, recovery and rebuild, focussing on Facebook and Twitter. Following a mixed methodological design data was gathered in interviews with people who started local Facebook pages, and through digital media methods of data collection and computational analysis of public Facebook pages and a historical Twitter dataset gathered around eight different earthquake-related events between 2010 and 2013. Data is further analysed through discursive and narrative tools of inquiry. This research sheds light on communication practices in the drawn-out process of disaster recovery on the ground in connecting different modes of discourse. Examining the ongoing negotiation of networked identities through technologically mediated social practices during Canterbury’s rebuild, the connection between online environments and the city of Christchurch, as a physical place, is unpacked. This research subsequently develops a new methodology to study social media platforms and provide new and detailed information on both the communication practices in issue-based online publics and the ongoing negotiation of the impact of the Canterbury earthquakes through networked digital means.

Research papers, University of Canterbury Library

Previous research has found that the capacity to self-regulate is associated with a number of positive life outcomes and deficits in self-regulation have been linked with poorer life outcomes. Therefore, parent and child self-regulation is an important focus of the Positive Parenting Program for Teenagers (Teen Triple P). The aim of this study was to investigate if Group Teen Triple P was effective in promoting parental self-regulation and adolescent behaviour change in families affected by the earthquakes in Canterbury NZ between 2010 and 2012. METHOD: Five families with teenagers aged 12-16 years were recruited from among families participating in a Group Teen Triple P program specifically implemented by the education authorities for parents self-reporting long-term negative effects of the earthquakes on their family. A single-case multiple-baseline across participants design was used to examine change in target teenager behaviour. Measures of self-regulation skill acquisition were taken using a coding scheme devised for the study from transcripts of three telephone consultations and from three family discussions at pre-intervention, mid-intervention, and post-intervention. Parents and their child also completed questionnaires addressing adolescent functioning, the parent-adolescent relationship and parenting at pre- and post-intervention. RESULTS: The multiple-baseline data showed that parents were successful at changing targeted behaviour for their child. Analysis of the telephone consultations and family discussions showed that parents increased their self-regulation skills over the therapy period and there was positive change in adolescent behavior reported on the Strengths and Difficulties Questionnaire. Additionally, the results suggested that higher rates and levels of self-regulation in the parents were associated with greater improvements in adolescent behaviour. CONCLUSION: This study demonstrated that the Group Teen Triple P -Program was effective in promoting self-regulation in parents and behaviour change in adolescents, specifically in a post-disaster context.

Research papers, University of Canterbury Library

This project was initiated by ENGEO Limited and KiwiRail Holdings Limited to assess the stability of Slovens Creek Viaduct (specifically its western abutment) and a 3km section of rail corridor between Slovens Creek Viaduct and Avoca on the Midland Line (MDL). Commonly known as the scenic TranzAlpine rail journey (through Arthurs Pass National Park) the MDL connects Greymouth to Christchurch via Rolleston, where the MDL meets the Main South Line into Christchurch. The project area is approximately 40km southeast of Arthurs Pass Township, in the eastern extension of the Castle Hill Basin which is part of the Waimakariri Catchment and Canterbury Foothills. The field area is underlain by Rakaia Terrane, which is part of the Torlesse Composite Terrane forming the basement rock unit for the field area. Cretaceous-Tertiary rocks of the Castle Hill Basin overlie the basement strata and record a transgression-regression sequence, as well as mid-Oligocene submarine volcanism. The stratigraphic sequence in the Castle Hill Basin, and its eastern extension to Avoca, comprises two formations of the Eyre group, the older Broken River Formation and the younger Iron Creek Formation. Deep marine Porter Group limestones, marls, and tuffs of Oligocene age succeed the Iron Creek Formation of the Eyre Group, and probably records the maximum of the transgression. The Enys Formation lies disconformably on the Porter Group and is overlain unconformably by Late Pleistocene glacifluvial and glacial deposits. The Tertiary strata in the Slovens-Avoca rail corridor are weak, and the clay-rich tuff derived from mid-Oligocene volcanism is particularly prone to slaking. Extensive mapping carried out for this project has identified that some 90 percent of the surface along the length of the Slovens-Avoca corridor has been subject to mass movement. The landslides of the Slovens-Avoca rail corridor are clearly younger than the Last Glaciation, and Slovens Creek has been downcutting, with associated faulting and uplift, to form the present day geomorphology of the rail corridor. Deep-seated landslides in the rail corridor extend to Slovens Creek, locally deflecting the stream course, and a generic ground failure model for the rail corridor has been developed. Exploratory geotechnical investigations, including core drilling, installation of an inclinometer and a piezometer, enabled the construction of a simple ground model and cross section for the Slovens Creek Viaduct western abutment. Limit-equilibrium and pseudo-static slope stability analyses using both circular and block critical slip surface search methods were applied to the ground model for the western abutment of Slovens Creek Viaduct. Piezometric and strength data obtained during laboratory testing of core material have been used to constrain the western abutment stability assessment for one representative section line (C-C’). Prior to pseudo-static sensitivity analyses peak ground acceleration (PGA) for various Ultimate Limit State (ULS) design return periods, defined by an equation given in NZS1170.5:2004, were calculated and have been used as a calibration technique to find and compare specific PGA values for pseudo-static analyses in the Slovens Creek Viaduct area. The main purpose has been to provide an indication of how railway infrastructure could be affected by seismic events of various return periods defined by ULS design standards for the area. Limit equilibrium circular slip surface search methods, both grid search and auto refine search, indicated the slope is stable with a FoS greater than 1.0 returned from each, although one particular surface returned the lowest FoS in each. This surface is in the lower portion of the slope, adjacent to Slovens Stream and northeast of the MDL. As expected, pseudo-static analyses returned a lower FoS overall when compared to limit equilibrium analyses. The PGA analyses suggest that partial ground failure at the Slovens Creek Viaduct western abutment could occur in a 1 in 25-year return period event within materials on the slower slope beyond the immediate rail corridor. A ULS (1 in 500-year) event in the Slovens Creek Viaduct area would likely produce a PGA of ~0.9g, and the effects on the western abutment and rail infrastructure would most likely be catastrophic. Observed ground conditions for the western abutment of the Slovens Creek Viaduct suggest there is no movement within the landslide at depth within the monitoring timeframe of this project (22 May 2015 – 4 August 2015). Slope stability monitoring is recommended to be continued in two parts: (1) the inclinometer in BH1 is to be monitored on a six monthly basis for one year following completion of this thesis, and then annually unless ground movements become evident; and (2) surface movement monitoring should be installed using a fixed datum on the stable eastern abutment. Long-term stability management strategies for the Slovens Creek Viaduct western abutment are dependent upon future observed changes and ongoing monitoring. Hazard and risk assessment using the KiwiRail Qualitative Risk Assessment Framework (QRA) is recommended, and if slope stability becomes problematic for operation of the Midland Line consideration should be given to deep slope drainage. In the event of a large magnitude or high PGA earthquake all monitoring should be reviewed.

Research papers, University of Canterbury Library

Liquefaction-induced lateral spreading in large seismic events often results in pervasive and costly damage to engineering structures and lifelines, making it a critical component of engineering design. However, the complex nature of this phenomenon leads to designing for such a hazard extremely challenging and there is a clear for an improved understanding and predicting liquefaction-induced lateral spreading. The 2010-2011 Canterbury (New Zealand) Earthquakes triggered severe liquefaction-induced lateral spreading along the streams and rivers of the Christchurch region, causing extensive damage to roads, bridges, lifelines, and structures in the vicinity. The unfortunate devastation induced from lateral spreading in these events also rendered the rare opportunity to gain an improved understanding of lateral spreading displacements specific to the Christchurch region. As part of this thesis, the method of ground surveying was employed following the 4 September 2010 Darfield (Mw 7.1) and 22 February 2011 Christchurch (Mw 6.2) earthquakes at 126 locations (19 repeated) throughout Christchurch and surrounding suburbs. The method involved measurements and then summation of crack widths along a specific alignment (transect) running approximately perpendicular to the waterway to indicate typically a maximum lateral displacement at the bank and reduction of the magnitude of displacements with distance from the river. Rigorous data processing and comparisons with alternative measurements of lateral spreading were performed to verify results from field observations and validate the method of ground surveying employed, as well as highlight the complex nature of lateral spreading displacements. The welldocumented field data was scrutinized to gain an understanding of typical magnitudes and distribution patterns (distribution of displacement with distance) of lateral spreading observed in the Christchurch area. Maximum displacements ranging from less than 10 cm to over 3.5 m were encountered at the sites surveyed and the area affected by spreading ranged from less than 20 m to over 200 m from the river. Despite the highly non-uniform displacements, four characteristic distribution patterns including large, distributed ground displacements, block-type movements, large and localized ground displacements, and areas of little to no displacements were identified. Available geotechnical, seismic, and topographic data were collated at the ground surveying sites for subsequent analysis of field measurements. Two widely-used empirical models (Zhang et al. (2004), Youd et al. (2002)) were scrutinized and applied to locations in the vicinity of field measurements for comparison with model predictions. The results indicated generally poor correlation (outside a factor of two) with empirical predictions at most locations and further validated the need for an improved, analysis- based method of predicting lateral displacements that considers the many factors involved on a site-specific basis. In addition, the development of appropriate model input parameters for the Youd et al. (2002) model led to a site-specific correlation of soil behavior type index, Ic, and fines content, FC, for sites along the Avon River in Christchurch that matched up well with existing Ic – FC relationships commonly used in current practice. Lastly, a rigorous analysis was performed for 25 selected locations of ground surveying measurements along the Avon River where ground slope conditions are mild (-1 to 2%) and channel heights range from about 2 – 4.5 m. The field data was divided into categories based on the observed distribution pattern of ground displacements including: large and distributed, moderate and distributed, small to negligible, and large and localized. A systematic approach was applied to determine potential critical layers contributing to the observed displacement patterns which led to the development of characteristic profiles for each category considered. The results of these analyses outline an alternative approach to the evaluation of lateral spreading in which a detailed geotechnical analysis is used to identify the potential for large spreading displacements and likely spatial distribution patterns of spreading. Key factors affecting the observed magnitude and distribution of spreading included the thickness of the critical layer, relative density, soil type and layer continuity. It was found that the large and distributed ground displacements were associated with a thick (1.5 – 2.5 m) deposit of loose, fine to silty sand (qc1 ~4-7 MPa, Ic 1.9-2.1, qc1n_cs ~50-70) that was continuous along the bank and with distance from the river. In contrast, small to negligible displacements were characterized by an absence of or relatively thin (< 1 m), discontinuous critical layer. Characteristic features of the moderate and distributed displacements were found to be somewhere between these two extremes. The localized and large displacements showed a characteristic critical layer similar to that observed in the large and distributed sites but that was not continuous and hence leading to the localized zone of displacement. The findings presented in this thesis illustrate the highly complex nature of lateral displacements that cannot be captured in simplified models but require a robust geotechnical analysis similar to that performed for this research.

Research papers, University of Canterbury Library

Following the 22nd February 2011, Mw 6.2 earthquake located along a previously unknown fault beneath the Port Hills of Christchurch, surface cracking was identified in contour parallel locations within fill material at Quarry Road on the lower slopes of Mount Pleasant. GNS Science, in the role of advisor to the Christchurch City Council, concluded that these cracks were a part of a potential rotational mass movement (named zone 11A) within the fill and airfall loess material present. However, a lack of field evidence for slope instability and an absence of laboratory geotechnical data on which slope stability analysis was based, suggested this conclusion is potentially incorrect. It was hypothesised that ground cracking was in fact due to earthquake shaking, and not mass movement within the slope, thus forming the basis of this study. Three soil units were identified during surface and subsurface investigations at Quarry Road: fill derived from quarry operations in the adjacent St. Andrews Quarry (between 1893 and 1913), a buried topsoil, and underlying in-situ airfall loess. The fill material was identified by the presence of organic-rich topsoil “clods” that were irregular in both size (∼10 – 200 mm) and shape, with variable thicknesses of 1 – 10 m. Maximum thickness, as indicated by drill holes and geophysical survey lines, was identified below 6 Quarry Road and 7 The Brae where it is thought to infill a pre-existing gully formed in the underlying airfall loess. Bearing strength of the fill consistently exceeded 300 kPa ultimate below ∼500 mm depth. The buried topsoil was 200 – 300 mm thick, and normally displayed a lower bearing strength when encountered, but not below 300 kPa ultimate (3 – 11 blows per 100mm or ≥100 kPa allowable). In-situ airfall loess stood vertically in outcrop due to its characteristic high dry strength and also showed Scala penetrometer values of 6 – 20+ blows per 100 mm (450 – ≥1000 kPa ultimate). All soils were described as being moist to dry during subsurface investigations, with no groundwater table identified during any investigation into volcanic bedrock. In-situ moisture contents were established using bulk disturbed samples from hand augers and test pitting. Average moisture contents were low at 9% within the fill, 11 % within the buried topsoil, and 8% within the airfall loess: all were below the associated average plastic limit of 17, 15, and 16, respectively, determined during Atterberg limit analysis. Particle size distributions, identified using the sieve and pipette method, were similar between the three soil units with 11 – 20 % clay, 62 – 78 % silt, and 11 – 20 % fine sand. Using these results and the NZGS soil classification, the loess derived fill and in-situ airfall loess are termed SILT with some clay and sand, and the buried topsoil is SILT with minor clay and sand. Dispersivity of the units was found using the Emerson crumb test, which established that the fill can be non- to completely dispersive (score 0 – 4). The buried topsoil was always non-dispersive (score 0), and airfall loess completely dispersive (score 4). Values for cohesion (c) and internal friction angle (φ) of the three soil units were established using the direct shear box at field moisture contents. Results showed all soil units had high shear strengths at the moisture contents tested (c = 18 – 24 kPa and φ = 42 – 50°), with samples behaving in a brittle fashion. Moisture content was artificially increased to 16% within the buried topsoil, which reduced the shear strength (c = 10 kPa, φ = 18°) and allowed it to behave plastically. Observational information indicating stability at Quarry Road included: shallow, discontinuous, cracks that do not display vertical offset; no scarp features or compressional zones typical of landsliding; no tilted or deformed structures; no movement in inclinometers; no basal shear zone identified in logged core to 20 m depth; low field moisture contents; no groundwater table; and high soil strength using Scala penetrometers. Limit equilibrium analysis of the slope was conducted using Rocscience software Slide 5.0 to verify the slope stability identified by observational methods. Friction, cohesion, and density values determined during laboratory were input into the two slope models investigated. Results gave minimum static factor of safety values for translational (along buried topsoil) and rotational (in the fill) slides of 2.4 – 4.2. Sensitivity of the slope to reduced shear strength parameters was analysed using c = 10 kPa and φ = 18° for the translational buried topsoil plane, and a cohesion of 0 kPa within the fill for the rotational plane. The only situation that gave a factor of safety <1.0 was in nonengineered fill at 0.5 m depth. Pseudostatic analysis based on previous peak ground acceleration (PGA) values for the Canterbury Earthquake Sequence, and predicted PGAs for future Alpine Fault and Hope Fault earthquakes established minimum factor of safety values between 1.2 and 3.3. Yield acceleration PGAs were computed to be between 0.8g and 1.6g. Based on all information gathered, the cracking at Quarry Road is considered to be shallow deformation in response to earthquake shaking, and not due to deep-seated landsliding. It is recommended that the currently bare site be managed by smoothing the land, installing contour drainage, and bioremediation of the surface soils to reduce surface water infiltration and runoff. Extensive earthworks, including removal of the fill, are considered unnecessary. Any future replacement of housing would be subject to site-specific investigations, and careful foundation design based on those results.

Research papers, University of Canterbury Library

This report provides an initial overview and gap analysis of the multi-hazards interactions that might affect fluvial and pluvial flooding (FPF) hazard in the Ōpāwaho Heathcote catchment. As per the terms of reference, this report focuses on a one-way analysis of the potential effects of multi-hazards on FPF hazard, as opposed to a more complex multi-way analysis of interactions between all hazards. We examined the relationship between FPF hazard and hazards associated with the phenomena of tsunamis; coastal erosion; coastal inundation; groundwater; earthquakes; and mass movements. Tsunamis: Modelling research indicates the worst-case tsunami scenarios potentially affecting the Ōpāwaho Heathcote catchment are far field. Under low probability, high impact tsunami scenarios waves could travel into Pegasus Bay and the Avon-Heathcote Estuary Ihutai, reaching the mouth and lower reaches of the Heathcote catchment and river, potentially inundating and eroding shorelines in sub-catchments 1 to 5, and temporarily blocking fluvial drainage more extensively. Any flooding infrastructure or management actions implemented in the area of tsunami inundation would ideally be resilient to tsunami-induced inundation and erosion. Model results currently available are a first estimate of potential tsunami inundation under contemporary sea and land level conditions. In terms of future large tsunami events, these models likely underestimate effects in riverside sub-catchments, as well as effects under future sea level, shoreline and other conditions. Also of significance when considering different FPF management structures, it is important to be mindful that certain types of flood structures can ‘trap’ inundating water coming from ocean directions, leading to longer flood durations and salinization issues. Coastal erosion: Model predictions indicate that sub-catchments 1 to 3 could potentially be affected by coastal erosion by the timescale of 2065, with sub-catchments 1-6 predicted to be potentially affected by coastal erosion by the time scale of 2115. In addition, the predicted open coast effects of this hazard should not be ignored since any significant changes in the New Brighton Spit open coast would affect erosion rates and exposure of the landward estuary margins, including the shorelines of the Ōpāwaho Heathcote catchment. Any FPF flooding infrastructure or management activities planned for the potentially affected sub-catchments needs to recognise the possibility of coastal erosion, and to have a planned response to the predicted potential shoreline translation. Coastal inundation: Model predictions indicate coastal inundation hazards could potentially affect sub-catchments 1 to 8 by 2065, with a greater area and depth of inundation possible for these same sub-catchments by 2115. Low-lying areas of the Ōpāwaho Heathcote catchment and river channel that discharge into the estuary are highly vulnerable to coastal inundation since elevated ocean and estuary water levels can block the drainage of inland systems, compounding FPF hazards. Coastal inundation can overwhelm stormwater and other drainage network components, and render river dredging options ineffective at best, flood enhancing at worst. A distinction can be made between coastal inundation and coastal erosion in terms of the potential impacts on affected land and assets, including flood infrastructure, and the implications for acceptance, adaptation, mitigation, and/or modification options. That is, responding to inundation could include structural and/or building elevation solutions, since unlike erosion, inundation does not necessarily mean the loss of land. Groundwater: Groundwater levels are of significant but variable concern when examining flooding hazards and management options in the Ōpāwaho Heathcote catchment due to variability in soils, topographies, elevations and proximities to riverine and estuarine surface waterbodies. Much of the Canterbury Plains part of the Ōpāwaho Heathcote catchment has a water table that is at a median depth of <1m from the surface (with actual depth below surface varying seasonally, inter-annually and during extreme meteorological events), though the water table depth rapidly shifts to >6m below the surface in the upper Plains part of the catchment (sub-catchments 13 to 15). Parts of Waltham/Linwood (sub-catchments 5 & 6) and Spreydon (sub-catchment 10) have extensive areas with a particularly high water table, as do sub-catchments 18, 19 and 20 south of the river. In all of the sub-catchments where groundwater depth below surface is shallow, it is necessary to be mindful of cascading effects on liquefaction hazard during earthquake events, including earthquake-induced drainage network and stormwater infrastructure damage. In turn, subsidence induced by liquefaction and other earthquake processes during the CES directly affected groundwater depth below surface across large parts of the central Ōpāwaho Heathcote catchment. The estuary margin of the catchment also faces increasing future challenges with sea level rise, which has the potential to elevate groundwater levels in these areas, compounding existing liquefaction and other earthquake associated multi-hazards. Any increases in subsurface runoff due to drainage system, development or climate changes are also of concern for the loess covered hill slopes due to the potential to enhance mass movement hazards. Earthquakes: Earthquake associated vertical ground displacement and liquefaction have historically affected, or are in future predicted to affect, all Ōpāwaho Heathcote sub-catchments. During the CES, these phenomena induced a significant cascades of changes in the city’s drainage systems, including: extensive vertical displacement and liquefaction induced damage to stormwater ‘greyware’, reducing functionality of the stormwater system; damage to the wastewater system which temporarily lowered groundwater levels and increased stormwater drainage via the wastewater network on the one hand, creating a pollution multi-hazard for FPF on the other hand; liquefaction and vertical displacement induced river channel changes affected drainage capacities; subsidence induced losses in soakage and infiltration capacities; changes occurred in topographic drainage conductivity; estuary subsidence (mainly around the Ōtākaro Avon rivermouth) increased both FPF and coastal inundation hazards; estuary bed uplift (severe around the Ōpāwaho Heathcote margins), reduced tidal prisms and increased bed friction, producing an overall reduction the waterbody’s capacity to efficiently flush catchment floodwaters to sea; and changes in estuarine and riverine ecosystems. All such possible effects need to be considered when evaluating present and future capacities of the Ōpāwaho Heathcote catchment FPF management systems. These phenomena are particularly of concern in the Ōpāwaho Heathcote catchment since stormwater networks must deal with constraints imposed by stream and river channels (past and present), estuarine shorelines and complex hill topography. Mass movements: Mass movements are primarily a risk in the Port Hills areas of the Ōpāwaho Heathcote catchment (sub-catchments 1, 2, 7, 9, 11, 16, 21), though there are one or two small but susceptible areas on the banks of the Ōpāwaho Heathcote River. Mass movements in the form of rockfalls and debris flows occurred on the Port Hills during the CES, resulting in building damage, fatalities and evacuations. Evidence has also been found of earthquake-triggered tunnel gully collapsesin all Port Hill Valleys. Follow-on effects of these mass movements are likely to occur in major future FPF and other hazard events. Of note, elevated groundwater levels, coastal inundation, earthquakes (including liquefaction and other effects), and mass movement exhibit the most extensive levels of multi-hazard interaction with FPF hazard. Further, all of the analysed multi-hazard interactions except earthquakes were found to consistently produce increases in the FPF hazard. The implications of these analyses are that multihazard interactions generally enhance the FPF hazard in the Ōpāwaho Heathcote catchment. Hence, management plans which exclude adjustments for multi-hazard interactions are likely to underestimate the FPF hazard in numerous different ways. In conclusion, although only a one-way analysis of the potential effects of selected multi-hazards on FPF hazard, this review highlights that the Ōpāwaho Heathcote catchment is an inherently multi- hazard prone environment. The implications of the interactions and process linkages revealed in this report are that several significant multi-hazard influences and process interactions must be taken into account in order to design a resilient FPF hazard management strategy.