Current research in geotechnical engineering at the University of Canterbury includes a number of laboratory testing programmes focussed on understanding the behaviour of natural soil deposits in Christchurch during the 2010-2011 Canterbury Earthquake Sequence. Many soils found in Christchurch are sands or silty sands with little to no plasticity, making them very difficult to sample using established methods. The gel-push sampling methodology, developed by Kiso-Jiban Consultants in Japan, was developed to address some of the deficiencies of existing sampling techniques and has been deployed on two projects in Christchurch. Gel push sampling is carried out with a range of samplers which are modified versions of existing technology, and the University of Canterbury has acquired three versions of the tools (GP-S, GP-Tr, GP-D). Soil samples are extracted from the bottom of a freshly drilled borehole and are captured within a liner barrel, close to 1m in length. A lubricating polymer gel coats the outside of the soil sample as it enters the liner barrel. The frictional rubbing which normally occurs on the sides of the soil samples using existing techniques is eliminated by the presence of the polymer gel. The operation of the gel-push samplers is significantly more complicated than conventional push-tube samplers, and in the initial trials a number of operational difficulties were encountered, requiring changes to the sampling procedures. Despite these issues, a number of high quality soil samples were obtained on both projects using the GP-S sampler to capture silty soil. Attempts were made to obtain clean sands using a different gel-push sampler (GP-TR) in the Red Zone. The laboratory testing of these sands indicated that they were being significantly disturbed during the sampling and/or transportation procedures. While it remains too early to draw definitive conclusions regarding the performance of the gel-push samplers, the methodology has provided some promising results. Further trialling of the tools are required to refine operating procedures understand the full range of soil conditions which can be successfully sampled using the tools. In parallel with the gel-push trials, a Dames and Moore fixed-piston sampler has been used by our research partners from Berkeley to obtain soil samples at a number of sites within Christchurch. This sampler features relatively short (50cm), thin-walled liner barrels which is advanced into the ground under the action of hydraulic pressure. By reducing the overall length of the soil being captured, the disturbance to the soil as it enters the liner barrel is significantly reduced. The Dames and Moore sampler is significantly easier to operate than the gel-push sampler, and past experience has shown it to be successful in soft, plastic materials (i.e. clays and silty clays). The cyclic resistance of one silty clay obtained using both the gel-push and Dames & Moore samplers has been found to be very similar, and ongoing research aims to establish whether similar results are obtained for different soil types, including silty materials and clean sands.
Between 2010 and 2011, Canterbury experienced a series of four large earthquake events with associated aftershocks which caused widespread damage to residential and commercial infrastructure. Fine grained and uncompacted alluvial soils, typical to the Canterbury outwash plains, were exposed to high peak ground acceleration (PGA) during these events. This rapid increase in PGA induced cyclic strain softening and liquefaction in the saturated, near surface alluvial soils. Extensive research into understanding the response of soils in Canterbury to dynamic loading has since occurred. The Earthquake Commission (EQC), the Ministry of Business and Employment (MBIE), and the Christchurch City Council (CCC) have quantified the potential hazards associated with future seismic events. Theses bodies have tested numerous ground improvement design methods, and subsequently are at the forefront of the Canterbury recovery and rebuild process. Deep Soil Mixing (DSM) has been proven as a viable ground improvement foundation method used to enhance in situ soils by increasing stiffness and positively altering in situ soil characteristics. However, current industry practice for confirming the effectiveness of the DSM method involves specific laboratory and absolute soil test methods associated with the mixed column element itself. Currently, the response of the soil around the columns to DSM installation is poorly understood. This research aims to understand and quantify the effects of DSM columns on near surface alluvial soils between the DSM columns though the implementation of standardised empirical soil test methods. These soil strength properties and ground improvement changes have been investigated using shear wave velocity (Vs), soil behaviour and density response methods. The results of the three different empirical tests indicated a consistent improvement within the ground around the DSM columns in sandier soils. By contrast, cohesive silty soils portrayed less of a consistent response to DSM, although still recorded increases. Generally, within the tests completed 50 mm from the column edge, the soil response indicated a deterioration to DSM. This is likely to be a result of the destruction of the soil fabric as the stress and strain of DSM is applied to the un‐mixed in situ soils. The results suggest that during the installation of DSM columns, a positive ground effect occurs in a similar way to other methods of ground improvement. However, further research, including additional testing following this empirical method, laboratory testing and finite 2D and 3D modelling, would be useful to quantify, in detail, how in situ soils respond and how practitioners should consider these test results in their designs. This thesis begins to evaluate how alluvial soils tend to respond to DSM. Conducting more testing on the research site, on other sites in Christchurch, and around the world, would provide a more complete data set to confirm the results of this research and enable further evaluation. Completing this additional research could help geotechnical DSM practitioners to use standardised empirical test methods to measure and confirm ground improvement rather than using existing test methods in future DSM projects. Further, demonstrating the effectiveness of empirical test methods in a DSM context is likely to enable more cost effective and efficient testing of DSM columns in future geotechnical projects.
The assessment of damage and remaining capacity after an earthquake is an immediate measure to determine whether a reinforced concrete (RC) building is usable and safe for occupants. The recent Christchurch earthquake (22 February 2011) caused a uniquely severe level of structural damage to modern buildings, resulting in extensive damage to the building stock. About 60% of damaged multistorey concrete buildings (3 storeys and up) were demolished after the earthquake, and the cost of reconstruction amounted to 40 billion NZD. The aftermath disclosed issues of great complexities regarding the future of the RC buildings damaged by the earthquakes. This highlighted the importance of post-event decision-making, as the outcome will allow the appropriate course of action—demolition, repair or acceptance of the existing building—to be considered. To adopt the proper strategy, accurate assessment of the residual capacity and the level of damage is required. This doctoral dissertation aims to assess the damage and remaining capacity at constituent material and member level (i.e., concrete material and beams) through a systematic approach in an attempt to address part of an existing gap in the available literature. Since the residual capacity of RC members is not unique and depends on previously applied loading history, post-event residual capacity in this study was assessed in terms of fraction of fatigue life (i.e., the number of cycles required to failure). This research comprises three main parts: (1) residual capacity and damage assessment at material level (i.e., concrete), (2) post-yield bond deterioration and damage assessment at the interface of steel and concrete, and, finally, (3) residual capacity and damage assessment at member level (i.e., RC beam). The first part of this research focused on damage assessment and the remaining capacity of concrete from a material point of view. It aimed to employ appropriate and reliable durability-based testing and image-detection techniques to quantify deterioration in the mechanical properties of concrete on the basis that stress-induced damage occurred in the microstructural system of the concrete material. To this end, in the first phase, a feasibility study was conducted in which a combination of oxygen permeability, electrical resistivity and porosity tests were assessed to determine if they were robust and reliable enough to reveal damage which occurred in the microstructural system of concrete. The results, in terms of change in permeability, electrical resistivity and porosity features of disk samples taken from the middle third of damaged concrete cylinders (200 mm × 100 mm) monotonically pre-loaded to 50%, 70%, 90% and 95% of the ultimate strength (f′c), showed the permeability test is a reliable tool to identify the degree of damage, due to its high sensitivity to the load-induced microcracking. In parallel, to determine the residual capacity, the companion damaged concrete cylinders already loaded to the same level of compressive strength were reloaded up to failure. Comparing the stress–strain relationship of damaged concrete with intact material, it was also found that the strain capacity of the reloaded pre-damaged concrete cylinders decreases while strength remained virtually unchanged. In the second phase of the first part, a fluorescent microscopy technique was used to assess the damage and develop a correlation between material degradation, by virtue of the geometrical features, and damage to the concrete. To account for the effect of confinement and cyclic loading, in the third phase, the residual capacity and damage assessment of unconfined and GFRP confined concrete cylinders subjected to low-cycle fatigue loading, was investigated. Similar to the first phase, permeability testing technique was used to provide an indirect evaluation of fatigue damage. Finally, in the fourth phase of the first part, the suitability of permeability testing technique to assess damage was evaluated for cored concrete taken from three types of RC members: columns, beams and a beam-column joint. In view of the fact that the composite action of an RC member is highly dependent on the bond between reinforcement and surrounding concrete, understanding the deterioration of the bond in the post-yield range of strain in steel was crucial to assess damage at member level. Therefore, in the second phase of this research, a state-of-the- art distributed fibre optic strain sensor system (DFOSSS) system was used to evaluate bond deterioration in a cantilever RC beam subjected to monotonic lateral loading. The technology allowed the continuous capture of strain, every 2.6 mm along the length, in both reinforcing bars and cover concrete. The strain profile provided a basis by which the slip, axial stress and bond stress distributions were then established. In the third part, the study focused on the damage assessment and residual capacity of seven half-scale RC beams subjected to a constant-amplitude cyclic loading protocol. In the first stage, the structural performances of three specimens under constant-amplitude fatigue at 1%, 2% and 4% chord rotation (drift) were examined. In parallel, the number of cycles to failure, degradation in strength, stiffness and energy dissipation were characterized. In the second stage, four RC beams were subjected to loading up to 70% and 90% of their fatigue life, at 2% and 4% drift, and then monotonically pulled up to failure. To determine the residual flexural capacity, the lateral force–displacement results of pre-damaged specimens were compared with an undamaged specimen subjected to only monotonic loading. The study showed significant losses in strength, deformability, stiffness and energy dissipation capacity. A nonlinear finite element analysis (FEA) using concrete damage plasticity (CDP) model was also conducted in ABAQUS to numerically investigate the behaviour of the tested specimen. The results of the FE simulations indicated a reasonable response compared with the behaviour of the test specimen in terms of force–displacement and cracking pattern. During the Christchurch earthquake it was observed that the loading history has a significant influence on structural responses. While in conventional pseudo-static loading protocol, internal forces can be redistributed along the plastic length: there is little chance for structures undergoing high initial loading amplitude to redistribute pertinent stresses. As a result, in the third phase of this part, the effect of high rate of loading on the behaviour of seismically designed RC beams was investigated. Two half-scale cantilever RC beams were subjected to similar constant-amplitude cyclic loading at 2% and 4% drifts, but at a rate of 500 mm/s. Due to the incapability of conventional measuring techniques, a motion-tracking system was employed for data acquisition with the high-speed tests. The effect of rate of loading on the fatigue life of specimens (i.e., the number of cycles required to failure), secant stiffness, failure mode, cracking pattern, beam elongations and bar fracture surface were analysed. Integrating the results of all parts of this research has resulted in a better understanding of residual capacity and the development of damage at both the material and member level by using a low-cycle fatigue approach.
Research on responses to trauma has historically focused on the negative repercussions of a struggle with adversity. However, more recently, researchers have begun to examine posttraumatic growth: the positive psychological change that emerges from the struggle with a potentially traumatic event. Associations have been found between posttraumatic growth and greater peritraumatic distress, greater objective severity of trauma exposure, greater perceived stressfulness of events, social support, female gender, cognitive and behavioural responses to trauma, and personality measures. Posttraumatic growth has been measured typically in individuals with varying levels of posttraumatic stress disorder symptoms and other psychological difficulties, such as depression and anxiety. Although some theory and research posits that higher resilience would prohibit posttraumatic growth, no studies have examined posttraumatic growth in a resilient sample. The Canterbury earthquake sequence of 2010 and 2011 involved potentially traumatic events that saw the community struggle with a variety of challenges. However, in the midst of earthquake destruction, some positive initiatives emerged, driven by locals. The Gap Filler project (using city spaces left empty from fallen buildings for art and interactive community projects) and the Student Volunteer Army (groups of volunteers coordinated to help others in need) are examples of this. In this context, it seemed likely that posttraumatic growth was occurring and might be seen in individuals who were coping well with challenges. Culture is theorised to influence the posttraumatic growth process (Calhoun, Cann, & Tedeschi, 2010), and the nature of the trauma undergone is also likely to influence the process of growth. The current thesis measures posttraumatic growth quantitatively and qualitatively in a New Zealand sample. It measures and describes posttraumatic growth in a resilient population after the earthquake sequence of 2010 and 2011 in Canterbury, New Zealand. Findings are used to test current models of posttraumatic growth for individuals coping well after trauma and to elaborate on mechanisms proposed by models such as the comprehensive model of posttraumatic growth (Calhoun et al., 2010) and the organismic valuing theory of growth through adversity (Joseph & Linley, 2005). Correlates of posttraumatic growth are examined and likely supporting factors of posttraumatic growth are identified for this population. Study 1 used quantitative analysis to explore correlates of posttraumatic growth and found that greater posttraumatic growth related to greater peritraumatic distress, greater perceived stressfulness of earthquake events, greater objective stressfulness of earthquake events, greater difficulty with stressful life events, less satisfaction with social support, and female gender. Findings from Study 1 give important detail about the nature of distress included in the comprehensive model of posttraumatic growth (Calhoun et al., 2010) for this population. Levels of posttraumatic growth were lower than those in North American studies but similar to those in a Chinese study. The current sample, however, showed lower endorsement of Relating to Others than the Chinese study, perhaps because of cultural differences. Study 2 used qualitative analysis to examine the experience of posttraumatic growth in the sample. The theme of ‘a greater sense of community’ was found and adds to the comprehensive model of posttraumatic growth, in that an expression of posttraumatic growth (a greater connection with others) can inform ongoing social processing in the posttraumatic growth process. Having a formal or informal role in earthquake recovery appeared to influence self-concept and reflection; this elaborates on the influence of role on reflection in Calhoun et al.’s model. Findings illustrate possible mechanisms of the organismic valuing process theorised by Joseph and Linley (2005). Implications include the importance of providing opportunities for individuals to take on a role after a crisis, encouraging them to act to respond to difficulties, and encouraging them to meet personal needs for relatedness, competence, and autonomy. Finding positive aspects to a difficult situation, as well as acknowledging adversity, can be supported in future to help individuals process their traumas. As a society, we can help individuals cope with adversity by providing ways they can meet their needs for relatedness, competence, and autonomy. Community groups likely provide opportunities for members to act in ways that meet such needs. This will allow them to effectively act to meet their needs in times of crisis.
Deconstruction, at the end of the useful life of a building, produces a considerable amount of materials which must be disposed of, or be recycled / reused. At present, in New Zealand, most timber construction and demolition (C&D) material, particularly treated timber, is simply waste and is placed in landfills. For both technical and economic reasons (and despite the increasing cost of landfills), this position is unlikely to change in the next 10 – 15 years unless legislation dictates otherwise. Careful deconstruction, as opposed to demolition, can provide some timber materials which can be immediately re-used (eg. doors and windows), or further processed into other components (eg. beams or walls) or recycled (‘cascaded’) into other timber or composite products (e.g. fibre-board). This reusing / recycling of materials is being driven slowly in NZ by legislation, the ‘greening’ of the construction industry and public pressure. However, the recovery of useful material can be expensive and uneconomic (as opposed to land-filling). In NZ, there are few facilities which are able to sort and separate timber materials from other waste, although the soon-to-be commissioned Burwood Resource Recovery Park in Christchurch will attempt to deal with significant quantities of demolition waste from the recent earthquakes. The success (or otherwise) of this operation should provide good information as to how future C&D waste will be managed in NZ. In NZ, there are only a few, small scale facilities which are able to burn waste wood for energy recovery (e.g. timber mills), and none are known to be able to handle large quantities of treated timber. Such facilities, with constantly improving technology, are being commissioned in Europe (often with Government subsidies) and this indicates that similar bio-energy (co)generation will be established in NZ in the future. However, at present, the NZ Government provides little assistance to the bio-energy industry and the emergence worldwide of shale-gas reserves is likely to push the economic viability of bio-energy further into the future. The behaviour of timber materials placed in landfills is complex and poorly understood. Degrading timber in landfills has the potential to generate methane, a potent greenhouse gas, which can escape to the atmosphere and cancel out the significant benefits of carbon sequestration during tree growth. Improving security of landfills and more effective and efficient collection and utilisation of methane from landfills in NZ will significantly reduce the potential for leakage of methane to the atmosphere, acting as an offset to the continuing use of underground fossil fuels. Life cycle assessment (LCA), an increasingly important methodology for quantifying the environmental impacts of building materials (particularly energy, and global warming potential (GWP)), will soon be incorporated into the NZ Green Building Council Greenstar rating tools. Such LCA studies must provide a level playing field for all building materials and consider the whole life cycle. Whilst the end-of-life treatment of timber by LCA may establish a present-day base scenario, any analysis must also present a realistic end-of-life scenario for the future deconstruction of any 6 new building, as any building built today will be deconstructed many years in the future, when very different technologies will be available to deal with construction waste. At present, LCA practitioners in NZ and Australia place much value on a single research document on the degradation of timber in landfills (Ximenes et al., 2008). This leads to an end-of-life base scenario for timber which many in the industry consider to be an overestimation of the potential negative effects of methane generation. In Europe, the base scenario for wood disposal is cascading timber products and then burning for energy recovery, which normally significantly reduces any negative effects of the end-of-life for timber. LCA studies in NZ should always provide a sensitivity analysis for the end-of-life of timber and strongly and confidently argue that alternative future scenarios are realistic disposal options for buildings deconstructed in the future. Data-sets for environmental impacts (such as GWP) of building materials in NZ are limited and based on few research studies. The compilation of comprehensive data-sets with country-specific information for all building materials is considered a priority, preferably accounting for end-of-life options. The NZ timber industry should continue to ‘champion’ the environmental credentials of timber, over and above those of the other major building materials (concrete and steel). End-of-life should not be considered the ‘Achilles heel’ of the timber story.
