Infrastructure Engineering - Theses
Now showing items 1-12 of 387
Understanding anastomosed landscapes through satellite and Indigenous eyes: A Nguku-Cooper Creek case study
The Nguku/KaRirra-Cooper Creek/Wilson River Confluence of the Kati Thanda (Lake Eyre) Basin, like many dryland water resources and associated ecologies, is increasingly under pressure from human activity and climate change. Sustainable water management requires quantitative monitoring of what is happening and when, why and how the effects are occurring, and who or what is causing change (positive or negative). This is especially difficult for such a temporary and heavily anastomosed river reach, due to its extreme natural variability, multi-year climate cycles, poorly tracked and slowly-responding ecology, sparse-instrumentation, and problematic access. Technical data about the Confluence can be sourced from measurements and satellite imagery, including 30 years of Landsat spectral data, verified during field expeditions. But technical data, with its limited duration, sampling frequency and extent, can only tell part of the story. A complementary source of information about the Confluence is the human lived experience, in the form of cultural stories that communities tell about their environment. The Indigenous Environmental Knowledge of the Wangkumara people of the KaRirra-Wilson River covers all parts of the Confluence hydrological cycle and interrelates it with cultural, historic, and ecological information. European accounts of exploration, re-naming, and settlement of the Nguku/KaRirra-Cooper Creek/Wilson River region from the 1800s to the present day are accessible through contemporaneous writings and maps and archives. Interviews with long-term residents provide information about more recent events. Archaeological studies further underpin knowledge that may hark back centuries or longer. This thesis develops a Worldview Methodology to address some of the major ethical and methodological challenges for academic researchers when accessing social and particularly Indigenous knowledge due to different systems of knowledge management and control, to promote appropriate use of Indigenous and other social knowledge in this contemporary hydrological study. The complicated Confluence landscape is systematized using Landscape Units, and its convergent/divergent drainage network is ordered by Extended Stream Order/Magnitude. Surface status is classified at pixel level using a three-way Water/Bare/Vegetated method, reflecting the significance of vegetation in tracking moisture. At feature level, waterholes are quantitatively assigned Permanent/ Intermittent/Ephemeral classifications. And at landscape level, Ribbon Plots illustrate spatial and statistical water presence over time along selected paths or transects. Using these tools to combines technical data, fieldwork, and Indigenous and social knowledge, this thesis tells a quantified cultural story of long-term water behaviour at the Nguku/KaRirra-Cooper Creek/Wilson River Confluence. It investigates three claims by current Confluence residents of flow behaviour changes as a result of construction work, plus one hydrological examination of a Wangkumara Story, quantifying how the journey of ancestral spirit Marnpi the Bronzewing Pigeon across a difficult arid landscape identifies persistent waterholes and other ecological features. The examples in this thesis show how interpretation of technical data can be improved by integration with the human lived experience via cultural stories. More broadly, the principles and methods can be applied to any multiple-channel, intermittent, or dryland system, allowing for more informed and inclusive environmental management. Ultimately, it shows social knowledge and Indigenous Environmental Knowledge are relevant to well-informed environmental management.
Spalling of concrete exposed to fire
Increasing usage of concrete materials in the building industry is related to their favourable characteristics such as durability, incombustibility, and low cost. However, fire accidents all around the world illustrate that the performance of concrete becomes vulnerable while exposed to a fire with a high heating rate such as hydrocarbon fire. This condition intensifies the occurrence of a phenomenon called “spalling”. Spalling is one of the most detrimental effects defined as a thermal instability in concrete when exposed to fire. Many experimental observations claim that when a concrete member is exposed to fire, some microcracks are generated both within and on the surface of the concrete. With the increase of temperature, the cracks develop further, and some pieces of concrete dislodge from the exposed surface, leading to exposure of steel reinforcement to high temperature in addition to the reduction of concrete cross-section result in capacity loss of concrete structural elements and even sometimes eventual failure of the entire structure. Despite the abundance of research, on fire performance of concrete members, researchers have not yet achieved a consensus agreement on the real physics of fire spalling and the relative contribution of the influencing factors on this phenomenon. Therefore, no unique and comprehensive guidelines are published for prevention of fire spalling in concrete structures. The erratic nature of spalling, inhomogeneous structure of concrete, and numerous and interdependent influencing factors results in a weak understanding of fire spalling of concrete exposed to fire. Unclear mechanism of spalling in concrete structures subjected to fire, increases the challenge for concrete designers for engineering application of high strength concrete (HSC) with a high risk of fire spalling, due to increasing usage of this material in new concrete structures such as high-rise buildings and tunnels. Based on the current research gap, this study aims to present a comprehensive study on the effect of influencing factors on fire spalling of concrete materials to achieve a clear view of the mechanism of spalling in both normal strength concrete (NSC) and high-strength concrete (HSC). The effect of cooling phase on fire performance of concrete structures is investigated through experimental and numerical analysis. The concrete structures are cooled down to room temperature after subjecting to fire and the specification and residual mechanical properties of the cooled down structure would be important for the future application of the heated concrete structure. The specification of the cooling down process including the duration of heating and the cooling rate on fire performance of concrete materials are also investigated on fire performance of concrete elements. The fire performance of concrete members is investigated in macro scale through experimental studies and microstructural analyses using Volume of Permeable Voids (VPV), Optical Microscope (OM), and Scanning Electron Microscope (SEM) tests. The achieved results indicate that higher density causes higher pore pressure inside HSC, which leads to higher porosity and generation of more cracks inside the concrete. The internal cracks reduce the stability of the HSC structure and make these types of concrete more vulnerable to fire spalling. Then, a thermo-mechanical finite element analysis (FEA) is conducted on reinforced concrete (RC) walls using Abaqus software, version 6.3. A previous experimental study is used to validate the numerical results and conduct a parametric study. The achieved results illustrate that the compressive strength of concrete is one of the main influencing factors governing the fire performance of concrete. Results indicate that unlike the NSC, thermal stress does not have a significant effect on fire spalling of HSC structures. In addition to the compressive strength, heating rate and specification of steel rebars have a considerable influence of fire performance of concrete. To develop the study of the fire spalling behaviour of concrete members, a thermo-hydromechanical FEA is then conducted to cover the effect of pore pressure in addition to thermal and mechanical stresses on fire spalling of concrete walls. Results achieved from the analysis highlight the difference in spalling mechanism of HSC and NSC. In HSC, the effect of pore pressure is more significant compared with the effect of thermal stress. On the other hand, in NSC thermal stress plays a more important role in fire spalling of concrete. Referring to the difference in the spalling mechanism of HSC and NSC, mitigation methods based on reducing the thermal gradient are necessary for NSC structures. Given the significant effect of porosity and pore pressure on the spalling of HSC members, mitigating methods to reduce or redistribute the generated pore pressure at high temperatures need to be considered in establishing a more applicable guideline for each type of concrete.
Collapse Behaviour of Prefabricated Modular Buildings Under Seismic Conditions
Modular construction is becoming increasingly popular day by day due to its’ advantages, that outweigh disadvantages to a great extent. With the continuous growth of modular construction, modular structures are moving more towards pure modular constructions which require minimal work onsite. Pure modular buildings require no external lateral force resisting systems (LFRS) which may require significant time and be more costly. Modular buildings are very different from conventional structures in terms of construction nature. A modular structure can be considered as an alternate arrangement of modules and connections. Hence, a modular building is discrete in terms of stiffness and strength distribution along with the building height, while that of a conventional building tend to be continuous. However, regardless of the apparent discrepancy between modular and conventional constructions in many aspects, modular structures are designed according to conventional building standards which fail to take inherent structural differences between modular and conventional structures into account. Furthermore, most of the connections used in modular structures resemble bolted connections which are used in conventional constructions. Bolted connections cannot provide sufficient ductility to a structure due to the brittle nature of failure involved in them. As the relative strength of the module is usually stronger than the inter-modular connections, failure is expected to occur at the connections when the rest of the building may remain in the elastic state. Hence, if this most critical connection is a bolted connection or some other connections which are not with sufficient energy-dissipating capacity, under a seismic event exceeding the design limit, the structure will result in a brittle failure initiated by the failure of connections. Moreover, since the connections form a single storey with high inelasticity concentration, failure of one connection may trigger the failure of other connections of the same storey in an unzipping manner across a storey. This may result in a plunge in the damage variation of the structure, resulting in adverse effects on the serviceability of the structure. Furthermore, an unzipping of connections across one storey may leave a colossal mass of structural component comprising a stack of modules to stand freely and overturn to collapse under a further increase in ground motion intensity. Pure modular structures are not fully realised in the current practice. However, since the current practice in modular construction is to rely on the conventional building design standards, techniques and practices, transformation to fully modular is not hindered from any of them. There are no rules or regulations in the current practise requiring external lateral force resisting systems (LFRS) for structures built in low to moderate seismic regions. Hence, if the structure without any external LFRS can still satisfy the code requirements, the structure can exist. Given the enormous time and cost savings from eliminating any external LFRS, designers might soon opt to move towards pure modular structures while still designing the structure as per conventional design standards. Some researchers have already investigated this transition. However, the risk involved in this transition, as discussed in the previous paragraph needs to be studied to come up with additional design considerations in designing pure modular structures rather than merely adhering to conventional code requirements. Even though the highlighted risk arises under higher seismic intensities (beyond design limits) which are a result of destructive intraplate earthquakes that are considered infrequent, the location of this type of future intraplate earthquakes cannot be predicted. When pure modular buildings become famous, they will start replacing the conventional structure throughout the world. Thus, the chance of such a building getting severely affected by an earthquake increase. The main aim of this study is to highlight the aforementioned potential risk involved in pure modular buildings that are built using conventionally available bolted connections when they undergo dynamic events exceeding their design intensity. A mid-rise (ten storeys) pure modular structure designed as per Australian design standards for Melbourne conditions was chosen as the prototype building to be considered in this study. Since the study aims at highlighting the risk involved in this construction nature when they are designed as per conventional building design standards without giving any special consideration, the study was conducted in comparison with a conventional steel frame analogical in physical dimensions to the chosen modular building. The study involved developing high-fidelity finite element (FE) models of the modular and conventional structures to study their feasibility and adherence to code requirements. Endurance time excitation functions (ETEF) were employed to study the seismic performance of the structure, especially under increasing seismic intensities. These ETEFs were developed as an alternative to conventional incremental dynamic analysis methods that are followed to study the seismic response of structures, more specifically, the collapse behaviour. The study is aimed at modelling the ultimate performance behaviour of the inter-modular connections between adjacent storeys as well as the near-collapse response behaviour of the building as a whole using numerical simulations along with shaking table experiments conducted on the shaker table for validation purposes. The simulations were scoped at investigating the behaviour of the building in a damaged state up to the onset of the wholesale collapse. Based on the collapse response observed in the FE models and during the experimental analysis on the shaking table, further numerical and experimental models were developed to simulate and study in-depth the collapse response of the modular structure. The study initiated with an investigation of the feasibility of the considered prototype modular and conventional steel buildings in terms of code requirements. Modal analysis, static pushover analysis and nonlinear dynamic analysis within the code specified limits proved that both the structures performed satisfactorily within the design limits. However, the modular structure was found to be failing catastrophically when the design limit exceeded, while the conventional steel frame continued to fail progressively. The discrete nature of the construction was highlighted during the analysis of prototype models, where the connections started giving up while the modules continued to remain in undamaged condition. Analysis of experimental and numerical models, together with the observations from the prototype FE models, revealed that the failure in the modular structure initiated from the failure of edge connections of the first storey. Failure of the edge connections resulted in a sudden increase in the stresses of the internal connections and a plunge in the global damage of the structure. The sudden increase in connection forces led to a failure of the internal connections of the first storey, resulting in a failure of all the connections of that storey in an unzipping manner. This resulted in the stack of modules above the first storey to be left as a free-standing block which experienced sliding, rocking, and overturning under the rest of the ground motion. The free-standing block thus formed (referred to as control model henceforth), analysed separately on the shaking table under the same ground motion stretch corresponding to the free-standing motion of the modular building superstructure, resulted in a pure rocking of the control model, without overturning. This observation was related to the absence of energy inputs (from the failure of connections just before the starting of free-standing phase), which results in initial conditions for the free-standing motion of the superstructure component, in the control model which was analysed on the shaking table. A numerical model of the control model, validated using the experimental results from the shaking table analysis was employed to verify the conclusion made on the cause of overturning with further analysis on it. Further, to support the conclusion, the ground displacement was checked against the half-width of the control model. The ground movement was way lesser than the half-width of the control model, supporting the fact that the energy released from the failure of the connections just before the free-standing motion was the sole reason for the overturning. Moreover, the validated numerical model of the control model was employed to understand and elaborate on factors exacerbating and mitigating overturning of the modular building superstructure. In contrast to the catastrophic failure that was observed in the modular structure, the conventional structure which comprised of a ductile braced frame demonstrated a failure initiation and progression through the bracing members which are not a primary component of the structure performance. Even though the prototype modular structure contained braces inside the modules, the lateral loadings that were resisted by the braces were finally transferred to the inter-modular connections. Moreover, since the braces (internal braces inside the modules) from upper and lower modules do not intersect at a single working point of the connection (due to the gap between the modules), the connections experience an unbalanced loading from the lateral loads transferred from upper and lower modules. This does not happen in the case of a conventional structure due to the continuous nature in the structure. Hence, in the conventional steel frame, the braces which have a higher ductile capacity gave up in a sequence, starting from lower storeys, moving up along the structure gradually. This sort of a distributed nature of the failure involving the failure of ductile components resulted in progressive failure of the conventional steel frame even beyond design limits. The hazardous nature of the collapse of pure modular structures, as highlighted in this study, is a critical study that has been lacking in the modular building research area. The need for this study arises explicitly due to the current practices followed in modular construction, which involves the use of conventional bolted connections as the inter-modular connections, and the use of conventional building design codes to design modular structures. As demonstrated through this study, the conventional design codes are capable of ensuring a safer performance of the conventional structures even beyond the design limits. In comparison, adherence to the same did not guarantee a safer performance of the modular structure beyond the design limits. Furthermore, this study brought out the unique nature of the failure initiation, progression and collapse involved in modular structures due to the discrete nature of its’ construction. This component of modular structures’ response has been missing in the research involved in modular structures, specifically under dynamic events. The collapse process, as studied in-depth in this research, can be utilised to improve the safety of the response of modular structures under dynamic loadings and come up with a safer pure modular system. Based on the findings from this study on the collapse response of conventional and modular structures, recommendations are presented at the end of this study for future researchers and designers to follow in designing pure modular structures. These recommendations are made by critically analysing and comparing the performance of the modular and conventional structures and by addressing what has been missing in the response of modular structures that makes its response catastrophic.
The physical internet for city logistics
The marketplace for city logistics is being shaped by the explosive growth of freight jobs and higher time sensitivity requirements due to e-commerce. There are more freight vehicles moving in urban areas now than ever before. These are primarily carried out by either professional logistics companies or crowdsourced delivery contractors. This urban freight boom generates higher levels of traffic congestion, adverse environmental impacts and other related effects that impact the overall quality of urban life. There is a need for innovative and effective solutions in city logistics by optimizing freight transportation systems within urban areas, especially to account for the fast growing market for on-demand and/or instant delivery jobs. The Physical Internet (PI) is a novel concept for freight transportation and city logistics that can potentially address this need. In the PI, freight carriers work in an open, sharing and collaborative system with interconnected operational networks. Although the conceptual framework and functional design for the PI and some of its components have been developed progressively in recent years, practical studies focused on implementation of the PI that engage different stakeholders and address their own objectives are lacking. This thesis investigates the implementation of the PI for reshaping city logistics, focused on the role and objectives of multiple stakeholders and the technological capabilities needed to bring the concept into practice. Addressing both tactical-level and operational-level issues, this thesis presents: (1) An auction-based open trading system that enables dynamic optimization of freight jobs’ allocation/reallocation amongst different stakeholders with multiple objectives for each stakeholder; this involves a multi-agent modelling approach to study the interaction of multiple self-interested agents in a complex environment; (2) The widespread parcel lockers or community stores to be used as transhipment hubs (PI-hubs) to enable flexible transhipment and interconnect multiple freight carriers; the PI-hub concept is supported by an auction-based open trading system with flexible transshipment and a solution to the transhipment-based routing problem for the interconnected network – a contribution to the Pickup and Delivery Problem with Transhipment and Time Windows; (3) A reinforcement learning (RL) enabled dynamic bidding strategy for freight carriers in the auction based freight transportation procurement platform to improve carriers’ decision making and actions in a stochastic and uncertain environment; and (4) An open trading system with consideration of multiple agents , in which the auction platform operator is considered as another self-interested agent as well. Multiple stakeholders including freight carriers, freight shippers and the auction platform operator make decentralized decisions based on achieving their own objectives where freight shippers aim to minimise freight costs, while freight carriers and the auction platform operator aim to maximise their own profit. The Deep Q Network based RL has been designed and used for multiple stakeholders to optimize their behaviour in a dynamic management environment. Multiple implementation scenarios have been simulated, and their results analysed and discussed based on a hypothetical network in Metropolitan Melbourne. In conclusion, on-line auctions, parcel lockers and RL contribute to the solution of bringing the PI concept into practice for city logistics. The two-stage on-line auction framework enables or supports an open and shared city logistics system. A parcel locker enabled interconnected network can further interconnect and optimize logistics operations. Reinforcement Learning is an intelligent method for improving stakeholders’ dynamic decisions for logistics management. Moreover, the Deep Q Network was demonstrated with better learning efficiency than some other learning approaches in the uncertain and fluctuating environment of city logistics.
Soil Gas Transport in Multiphase Materials for Prediction of Acid Mine Drainage
Abstract To assess the economic viability of a proposed mining project, a cost estimate for its mine waste management systems is required, including design and operations of structures such as waste rock dumps, tailing storage facilities and any associated waste treatment systems. In orebodies with sulfide mineralisation, such as coal and base metals, accurate cost estimates are especially important due to the potential high costs of acid mine drainage (AMD) waste management during mine operations and possibly in perpetuity. AMD is generated when sulfides are exposed to oxygen and moisture and sulfide oxidation occurs, creating acid (H2SO4) which can mobilise metals and other toxicants into surface and groundwaters, potentially causing damage to downstream aquatic ecosystems. Currently AMD is assessed and managed using a variety of demand-side, geochemical based testing and modelling techniques, such as humidity cells and leaching columns, which are often expensive, lengthy and complex studies. Due to the limitations of these tests, and the large numbers of parameters involved in geochemical testing and modelling, the results can often still underestimate the effects of AMD, potentially resulting in harm to aquatic ecosystems. The use of a supply-side approach to AMD oxidation, such as oxygen consumption techniques, and soil gas (oxygen) transport, to estimate the potential effects of AMD for mine waste management purposes, has been identified as a useful method that may offer an additional methodology for AMD assessment for geochemical engineers and mine waste managers. This research project seeks to contribute to a new methodology to mine waste management design for AMD mine materials, targeted at the mine design concept and prefeasibility phases. Its principle is based on the use of 1D or 2D soil gas (oxygen) transport models to provide an estimate of potential AMD mine waste volumes that may be oxidised and hence require stabilisation treatment. The soil gas transport models proposed provides for quick, practical and accurate volume assessments in waste rock dumps and waste tailing storage facilities. The proposed method combines lab testing to collect soil gas diffusion data for specific mine wastes, with soil gas transport modelling to test several soil gas diffusion models in 1D and 2D. Several configurations of soil gas diffusion columns were designed and tested over several iterations to provide fast (<3 hours) and economic soil gas diffusion estimates. These columns are designed to be built from commonly available UVPC stormwater pipe materials for less than $500 USD. The method is scalable to any size of project and can provide accurate AMD estimations by collecting additional mine materials soil and rock data for i) soil water characteristic curves (SWCC), ii) soil gas diffusion testing, and iii) soil oxygen penetration column tests. The thesis consists of 8 Chapters: Chapter 1 provides an overview of the problem and the research questions for this project. Chapter 2 presents a critical review of the available literature and Chapter 3 identifies the key knowledge gaps and summarises the research program objectives and work plan. The following three Chapters present results in the form of three journal Papers (two published, one under review) to document the research findings of the project. Chapter 4 presents (Paper i) an introductory Paper to describe the potential pitfalls and impacts of the methodology used for geochemical based AMD mine materials testing and matrix particle size on conceptual mine waste treatment costs. Chapter 5 (Paper ii) presents a comparative assessment of the existing soil gas diffusion coefficient estimation models available in the literature and Chapter 6 (Paper iii) explains the development of a 1D soil gas transport model and testing methodology for AMD mine waste volume determination. Chapter 7 details further development of the 1D model into a 2D finite difference model and demonstrates the additional accuracy of the 2D approach when applied to complex geometries such as sloped or cracked materials and mine waste structures such as tailing storage facilities and waste rock dumps. Chapter 8 presents the key findings and contributions from the research and identifies the key limitations of the work and future research directions. The findings of Paper i highlight the potential for exponential levels of multiplicative error when undertaking geochemical based assessment of AMD materials for treatment and mine closure purposes alone. The use of soil gas diffusion transport models to assess AMD material volumes can potentially contribute to reducing this error by providing additional material volume estimations for comparison, with lower rates of experimental error. Soil gas diffusion testing and related soil gas diffusion models can be compared and checked for potential error across soil and rock matrix types using literature-based diffusion testing results and matrix particle size analysis approaches. The importance of measurement of soil gas diffusion coefficients and the derivation of soil moisture vs soil gas diffusion responses for use in soil gas transport modelling of AMD material response in the mining sector was demonstrated and discussed in Paper ii. Reliance on single material diffusion coefficients, or diffusion coefficient estimation models in the literature was found to be problematic, due to the agricultural basis for these models. The soil gas diffusion risks for agriculture are opposite to that of the mining sector, drying soils with high diffusion coefficients are a risk for mining, while wetting soils with low diffusion coefficients are a risk for agriculture and crop production, and all diffusion coefficient models found in the literature were based on agricultural risk profiles. All commercial soil gas transport models evaluated during the project were found to include either single value diffusion coefficient-based functions, or agriculture-based diffusion coefficient estimation functions. A 1D soil gas diffusion model and methodology for assessing AMD impacted mine materials is presented in Paper iii. The Paper builds on the soil gas diffusion column method shown in Paper ii by adding an oxygen penetration column test to derive the boundary conditions required for the 1D model. The 1D model is used to evaluate the performance of several diffusion coefficient estimation models available in the literature. The discussion highlights the potential limitations and agricultural bias for several existing diffusion coefficient estimation models, analysis of possible dual diffusion functions based on soil matrix geometry and particle size and proposes the use of safety factors to ensure AMD material volume assessments are suitably conservative. The development of a simple spreadsheet based, finite difference 2D soil gas transport model derived from the 1D model is documented in Chapter 7. The 2D model was designed to work with measured soil moisture/diffusion coefficient models, single value diffusion coefficients, or diffusion coefficient models from the literature. Statistical 2D model performance evaluation was undertaken, and the results demonstrate the additional capability of the 2D model to provide accurate volume assessments of potentially AMD affected mine waste materials with complex geometries such as cracks and fractures, when using the soil gas diffusion transport method provided by this research project. The 2D model results again highlighted the importance of measurement of soil gas diffusion coefficient at several material moisture levels to provide a realistic soil gas diffusion model result for accurate geochemical and waste management design with AMD materials. The overall conclusion of the research project is that the use of the proposed soil gas diffusion measurement and modelling methodology provides a potential fast, economic and more accurate alternative to the complex suite of geochemical assessment methods currently used to estimate the rate of sulfide oxidation. The method is useful for assessing concept and prefeasibility mine design estimates of volumes of AMD mine materials and waste potentially requiring treatment. Testing the AMD mine materials for soil gas diffusion behaviour at a range of moisture levels provides the most accurate results, as many diffusion coefficient models available in the literature may underestimate AMD oxidation. The soil gas diffusion method is presented with an accuracy hierarchy, and the use of safety factors is explored to replace diffusion testing if use of the complete soil diffusion and oxygen penetration testing method presented in this thesis is not possible. When combined with detailed level geochemical assessments, the method offers a complimentary data source, suitable for detailed and final design of AMD waste management and treatment systems.
Engineering and economic impacts of sea level rise
Episodic flooding, due to extreme sea levels, can have major impacts on low-lying areas where 10% of the total world’s population resides. Combined with climate change induced sea level rise over the next century, the resulting impacts are likely to be exacerbated. One of the most obvious impact is the exposure of such areas to more frequent and increased extreme sea levels resulting in enhanced inundation extent. Global assessment of extreme sea levels together with the sea level rise component and their impacts is critical to assess the resilience and vulnerability of coastal zones. The present dissertation assesses these impacts on a global scale. The historical values of tide, storm surge, wave setup are reconstructed from recent reanalyses at global coastal locations. Both the sea levels and the extremes are rigorously validated against quasi-global tide gauge records. To determine extreme values, a variety of extreme value analysis methods are applied and compared against each other and the tide gauge records. Future projections of the extreme sea levels are determined in combination with sea level rise scenarios over the upcoming century. The extent of present and future episodic flooding resulting from the corresponding extreme sea levels are presented. The resulting impacts on the global population and assets at risk for present conditions and under various combinations of future socioeconomic scenarios. Global "hotspots", based on future changes in the flooding and extreme sea levels, are identified in this study to demonstrate coastal areas which potentially will be the most impacted by changes in extreme sea levels. These areas are mostly found to be concentrated in north western Europe and Asia. The results show that for the case of, no present/future coastal protection or adaptation, and a mean RCP8.5 scenario, there will be an increase of 48% of the world’s land area, 52% of the global population and 46\% of global assets at risk of flooding by 2100. Regional and national analyses are conducted in order to highlight the values of both Expected Annual Population Affected (EAPA) and Expected Annual Damage (EAD), globally. In order to define a more accurate representation of the global coastal flooding at the aggregated regions, estimated coastal defences are included under various socioeconomic narratives as well as possible adaptation strategies. It is shown that, by 2100 and without future adaptation, global values of EAPA are projected an increase by a factor 3.6 in terms of people impacted. For global values of EAD, the increase relative to present-day values is a factor of 25. It is also demonstrated that the change in the subcontinental regions show significant variations when compared to the present values. In particular, developing areas of Asia will experience significant impacts on both populations and GDP by 2100. These impacts of projected future flooding on the developing world will be far greater than for the developed world.
Developing the Extreme Wave Indicators for Spectral Model Using Phase Resolving Studies
The relation between rogue wave occurrence statistics and properties of the directional and unidirectional wind-wave spectrum, described by the JONSWAP spectrum, are investigated. The free surface statistics are obtained from phase-resolving simulations. The stochastic approach to rogue wave occurrence is conducted based on the quantitative indicator parameters, which are designed to represent instabilities in wave-trains. Numerical findings are compared with measurements. Further, extreme value analysis (EVA) has been applied to indicator parameters based on 40 years of global wave hindcast data.
Design enhancement and prefabrication of raft footings on clayey ground susceptible to reactive soil damage
The Architecture, Engineering and Construction (AEC) industry is currently facing several challenges. A failure to keep pace with technological advancements had led to non-optimal structural performance, inefficient construction process, and unsustainable consumption of raw materials. This failure to adapt to new technology precipitates an intensifying "housing crisis" being experienced in most developed and developing cities, attributed to an increase in housing demand and skilled labour shortage. Furthermore, the increasing occurrence of extreme weather events, natural disasters and unexpected situations necessitate expeditious post-disaster and temporary accommodations. Prefabricated construction has been considered as a potential solution to the challenges being faced by the AEC sector. However, the full potential of prefabricated construction is yet to be realised in part due to most developments being focused on its superstructure. Lightweight structures with shallow footings, such as single-detached dwellings, are particularly susceptible to damage caused by the shrink-swell movement of reactive soils, causing a significant global financial loss for the repair cost. Due to the lack of innovation in footing systems of lightweight structures and detrimental effects inflicted by the shrink-swell ground movement, the overarching aim of this research is to develop a prefabricated footing system on clayey foundations susceptible to damage induced by the shrink-swell movement of reactive soils, using an enhanced design method. To enhance the design method, an advanced yet practical three-dimensional coupled hydro-mechanical finite element model was developed to perform parametric simulations. This investigated the relationship between reactive soil movements and footing system deformation, which led to a deeper understanding of its soil-structure interaction and an improved design guideline. To develop the prefabricated footing design, a combined novel approach was introduced using soil-structure interaction analysis, topology optimisation and strut-and-tie model to design a connection. The prefabricated system had satisfactory structural performance based on numerical simulations that can potentially overcome most construction and performance limitations of conventional monolithic cast-in-situ footings.
Dynamic loads on prefabricated modular building unit during road transportation
Prefabricated modular construction is set to revolutionize the modern construction industry once again. Over the past couple of centuries, prefabrication has proven to be a more cost-efficient and time-saving alternative to conventional design practices. Computer-aided design has facilitated more complex projects in terms of architecture, planning and cost. Prefabricated construction has benefitted from the advent of building information modelling (BIM), 3-D printing, robotics, and assembly line automation. What is poised to become a multi-trillion-dollar industry in the coming decade, the modular construction is still navigating through its bottlenecks around different parts of the world. Benefits of doing lesser at the construction site and more at the offsite are pushing the frontiers of prefabricated modular construction every day. The demand for pre-furnished, all equipped plug-in ready modules has increased. With many issues pertaining to skilled labour availability, shipping, transportation, and erection issues, structural robustness, and project economics, yet to be resolved, the industry demand for prefabrication is ever increasing. The research undertaken in this project focused on quantifying the hazards due to road induced vibrations to the modular building unit and its internal components. A stepwise approach of the project quantified the vertical acceleration spectra for non-structural components inside the modules. The first part addressed the continuous vibrations sustained by the modular unit and the internal components due to road roughness. The second part calculated the impact-induced hazard by predicting the risk of the vertical separation between the module and the trailer-bed. Stochastic modelling was employed using stationary processes to create a large sample of road profiles consistent with the required roughness power spectral density functions. Multi-degree of freedom lumped mass model was developed to predict the truck trailer's response to the road profile roughness in the vertical plane. The truck-road numerical modelling was validated with field experiments on known road surfaces. Response acceleration spectra for the components attached to the modules carried by trailer were reported as the sustained dynamic actions on the cargo. A probabilistic estimate for vertical gap formation (and vertical impact velocity) between the strapped cargo (module) and the trailer-bed was made by extending the truck-road interaction model. The impact between the air-borne edge of the box module structure with that of the trailer-bed was studied analytically, numerically and experimentally. Component response acceleration spectra were derived for such a pounding scenario considering different masses of the modules impacting with different velocities. Design acceleration spectra for components were broadly classified into three frequency regimes (< 20 Hz, < 50 Hz, > 50 Hz) stipulating vertical acceleration demand of the non-structural component fixtures inside modules during transportation. Structural guidelines available for the component fixture design could only be found in seismic standards. What is typically sufficient for component design in conventional buildings may not be so for furnished modular structures as the transportation induced dynamic loads could be much higher than the seismic provisions for the non-structural components. This study offers guidelines for the capacity design of the internal fixtures of a fully furnished modular structural unit through numerical analysis backed by experimental tests. The findings of this study are expected to assist the engineers in designing the building utilities, suspended ceilings, non-structural walls, wall-mounted equipment of a modular building unit for transportation induced loads. Recommendations: 1. Incorporate higher design forces for internal component fixtures governed by the acceleration response spectra derived in the study. 2. Provide rigid latching between the MBU and the trailer-bed similar to that of the container shipping module. 3. In the case of larger MBUs that cannot be rigidly fastened to the trailer-bed, increase vertical tie strength to 40% of the total weight of the cargo to avoid vertical separation. 4. Incorporate softer palleting materials: a. To filter out high-frequency vibrations b. To alleviate the damage hazard during pounding should it occur. 5. Increase the support locations for the MBU by increasing the number of mounts/pallets used during transportation. 6. Orient the MBU on the trailer-bed such that vibration-sensitive components would lie in the front portion of the trailer.
Segment-based Classification of Mobile Lidar Point Clouds with Limited Samples
Mobile lidar data have been widely used in building 3D models, road mapping and inventorying, and nowadays in driverless car technology. Compared with traditional photogrammetry and remote sensing data acquisition methods, mobile lidar technology can collect precise 3D point cloud data more efficiently at driving speeds in urban environments, even in extreme weather conditions. Efficient processing of mobile lidar data, including object detection and recognition, is an active research field. Manual object detection and labelling is tedious, and it is limited by the variety of objects and the complexity of the environments in which the data is acquired. Therefore, the development of automated and efficient object recognition methods is important, but also challenging. A common procedure for automatic processing of 3D lidar data includes successive segmentation, classification and labeling of objects from initially unstructured point clouds. This segment-based classification of mobile lidar data essentially relies on local and global features extracted from point coordinates. These features are either hand-designed, as in traditional supervised machine learning, or automatically learned by more recent deep-learning-based methods. Compared with the traditional supervised machine learning methods, deep convolutional neural networks can learn high-level representations through compositions of low-level point information from large numbers of training samples. However, despite their remarkable success, deep networks require a large number of training samples which makes their application to mobile lidar point clouds very problematic. To overcome the limitation of training samples, transfer learning and domain adaptation methods have been introduced with the aim of transferring available information or knowledge from a source domain to a different target domain. The transfer learning methods can be roughly divided into two categories: shallow and deep. The shallow transfer learning methods such as weighting-based, feature-align-based and model-adjust-based have gained popularity for their succinctness and operability at the cost of shallow transferability. In contrast, end-to-end deep transfer learning methods have better high-level common feature extraction ability and better transferability. The aim of this research is to develop and evaluate methods for accurate segment-based classification of mobile lidar point clouds with limited training samples. The main contributions of this research are as follows. First, the ability of traditional machine learning using local feature extraction and encoding methods in classification with limited samples is investigated. Second, a method is proposed to take advantage of available complementary datasets by combining feature extraction in a deep network and shallow transfer learning by sample reweighting. Third, an end-to-end deep transfer learning method is proposed by extending a domain adaptation network from 2D to 3D for application to mobile lidar point clouds. Experimental evaluation of the methods indicates the significant potential of transfer learning methods to overcome the limitation of training samples and improve the classification accuracy of mobile lidar point clouds.
Study on air-sea CO2 gas exchange with wave breaking
Atmospheric CO2 is accumulating in recent decades due to excessive anthropogenic activities such as fossil fuel combustion, which intensifies global warming and affects the balance of carbon cycle. With more CO2 in the air, ocean which acts as one of the largest carbon reservoirs absorbs about 26% of the human emissions of CO2 to the atmosphere. The increased ocean inventory of anthropogenic carbon has caused the acidification of ocean water, making it critical to assess the CO2 gas transfer process at air-sea interface. CO2 gas transfer velocity (KCO2) is the main subject in the estimation of gas flux. To date, KCO2 is traditionally parameterized with wind speed, but it is the waves which produce the turbulence and bubbles that enhance the CO2 intake. In our work, the new parameterization of KCO2 with wave parameters is proposed through laboratory experiments, validated by field observation and applied to the estimation of the air-sea CO2 flux over global ocean. To investigate the direct relationship between CO2 gas transfer and waves, laboratory experiments are conducted in a wind-wave flume. Three kind of waves are forced in the flume: monochromatic waves generated by a wavemaker, mechanically-generated monochromatic waves with superimposed wind forcing, and pure wind waves with 10-meter wind speed ranging from 4.5 m/s to 15.5 m/s. The wave parameters are found to be well correlated with KCO2 while wind speed alone can not adequately describe KCO2. To reconcile the data sets, non-dimensional empirical formulae are established in which KCO2 is expressed as a function of wave parameters as the dominant term and an enhancement factor to account for additional influence of the wind. The parameterization is further validated by using field campaign data from different locations of open ocean and improved including considering the importance of bubble-mediated gas transfer at sea. The verified formula is able to collapse the results of both laboratory and field with reduced uncertainties. The net air-sea CO2 flux of global ocean is evaluated in a 33-year period from 1985 to 2017 by using our gas transfer parameterization. The results are in high agreement with previous studies, which is another evidence of the validity of the parameterization. A general increasing trend of global ocean net uptake of CO2 is observed. The CO2 flux in period 2017-2100 is also projected by using different CMIP6 forecast of future scenarios.
Evaluating Catchment Models as Multiple Working Hypotheses under Uncertainty
Catchment models are conventionally evaluated in terms of their response surface or likelihood surface constructed from model runs using different sets of model parameters. Model evaluation methods are mainly based upon the concept of the equifinality of model structures or parameter sets. The operational definition of equifinality is that multiple model structures/parameters are equally capable of producing acceptable simulations of catchment processes such as runoff. Examining various aspects of this convention, in this thesis I demonstrate their shortcomings and introduce improvements including new approaches and insights for evaluating catchment models as multiple working hypotheses (MWH). First (Chapter 2), arguing that there is more to equifinality than just model structures/parameters, I propose a theoretical framework to conceptualise various facets of equifinality, based on a meta-synthesis of a broad range of literature across geosciences, system theory, and philosophy of science. I distinguish between process-equifinality (equifinality within the real-world systems/processes) and model-equifinality (equifinality within models of real-world systems), explain various aspects of each of these two facets, and discuss their implications for hypothesis testing and modelling of hydrological systems under uncertainty. Second (Chapter 3), building up on this theoretical framework, I propose that characterising model-equifinality based on model internal fluxes — instead of model parameters which is the current approach to account for model-equifinality — provides valuable insights for evaluating catchment models. I developed a new method for model evaluation — called flux mapping — based on the equifinality of runoff generating fluxes of large ensembles of catchment model simulations (1 million model runs for each catchment). Evaluating the model behaviour within the flux space is a powerful approach, beyond the convention, to formulate testable hypotheses for runoff generation processes at the catchment scale. Third (Chapter 4), I further explore the dependency of the flux map of a catchment model upon the choice of model structure and parameterisation, error metric, and data information content. I compare two catchment models (SIMHYD and SACRAMENTO) across 221 Australian catchments (known as Hydrologic Reference Stations, HRS) using multiple error metrics. I particularly demonstrate the fundamental shortcomings of two widely used error metrics — i.e. Nash–Sutcliffe efficiency and Willmott’s refined index of agreement — in model evaluation. I develop the skill score version of Kling–Gupta efficiency (KGEss), and argue it is a more reliable error metric that the other metrics. I also compare two strategies of random sampling (Latin Hypercube Sampling) and guided search (Shuffled Complex Evolution) for model parameterisation, and discuss their implications in evaluating catchment models as MWH. Finally (Chapter 5), I explore how catchment characteristics (physiographic, climatic, and streamflow response characteristics) control the flux map of catchment models (i.e. runoff generation hypotheses). To this end, I formulate runoff generating hypotheses from a large ensemble of SIMHYD simulations (1 million model runs in each catchment). These hypotheses are based on the internal runoff fluxes of SIMHYD — namely infiltration excess overland flow, interflow and saturation excess overland flow, and baseflow — which represent runoff generation at catchment scale. I examine the dependency of these hypotheses on 22 different catchment attributes across 186 of the HRS catchments with acceptable model performance and sufficient parameter sampling. The model performance of each simulation is evaluated using KGEss metric benchmarked against the catchment-specific calendar day average observed flow model, which is more informative than the conventional benchmark of average overall observed flow. I identify catchment attributes that control the degree of equifinality of model runoff fluxes. Higher degree of flux equifinality implies larger uncertainties associated with the representation of runoff processes at catchment scale, and hence pose a greater challenge for reliable and realistic simulation and prediction of streamflow. The findings of this chapter provides insights into the functional connectivity of catchment attributes and the internal dynamics of model runoff fluxes.