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The present study investigates in detail the effects of the direct application of power ultrasound (PUS) at several frequencies and power densities to Portland cement (PC) pastes and mortars. The ultrasound frequencies of 26, 67 and 132 kHz that respectively correspond to power densities of 0.011, 0.007 and 0.003 W/cm³ were deployed to treatments of fresh cement pastes and mortars. These various ultrasound intensities were generated using a large bespoke, multi-frequency ultrasonic bath. A fixed ultrasonic bath operating at 40 kHz with a power density of 0.014 W/cm³ was also used to study the effects of PUS on the particle size distribution (PSD) of PC. In the first part of the study, changes in the PSD parameters of PC based on wet dispersion in both isopropanol (IPA) and deionised water (DI water) were determined using laser diffraction method. Next, ultrasound at various frequencies was directly applied to the fresh PC pastes at water-to-cement (w/c) ratios of 0.50 and 0.80. The chemical composition of the pore solution extracted from the fresh and hardened cement pastes were examined using the inductively coupled plasma optical emission spectrometry (ICP-OES) technique after applying ultrasound for various periods. The work presents a robust ICP-OES method developed to quantify both Ca, K, Na and S as the high-concentration analytes, and Al, Fe, Mg and Si as the low-concentration analytes in the PC paste pore solution. Additionally, hydrate assemblages were identified by X-ray diffraction (XRD). A semi-quantification of important components was performed using data obtained by thermogravimetric analyses (TGA/DTG). The changes in the setting times of cement pastes subjected to PUS were also reported. The PSD data shows that applying PUS for up to 5 minutes marginally deagglomerates the coarse size fraction of PC particles in aqueous dispersion. However, ultrasound may not be able to effectively disaggregate the PC particles in normal pastes, even at longer exposure; particularly the finer size fractions (< 10 μm). Direct application of PUS to the PC paste does not alter the main types of PC hydration products but appreciably changes the pore solution composition and slightly affects the main hydrate proportions and kinetics. The study reveals for the first time, that applying PUS can potentially disturb the early formation of ettringite, whilst appreciably promoting the formation of amorphous aluminium hydroxide hydrate by considerably releasing aluminium ions into pore solutions of cement pastes at both w/c ratios of 0.50 and 0.80. Upon ultrasound exposure (particularly at longer times), noticeable changes were observed in Ca and Si concentrations denoting the influence of PUS on the dissolution of alite and/or aluminate phases due to the cavitation. Moreover, PUS was shown for the first time to be able to increase carbonates by intensifying the carbonation (ultrasound-assisted carbonation) in the PC pastes, particularly in the system with a higher water content. In the next part of the study, the development of hydration under the exposure of ultrasound irradiation at various frequencies/power densities and durations was assessed. First, the effect of PUS on the extent of PC hydration was investigated by precisely measuring the chemical shrinkage, using a self-developed automated dilatometry method, to 14 days of hydration. To measure the evolution of chemical shrinkage, an automated vision inspection system was developed. Additionally, the mechanical performances of the PC mortars were evaluated at testing ages of 1, 3, 7, 28 and 91 days. Two different sonication procedures were adopted for the treatment of the fresh mortar mixes. This was to investigate the effect of applying ultrasound at various stages on the mechanical properties of mortars and the properties of the interface between the cement paste and the aggregates (interfacial transition zone, ITZ). In the first approach, ultrasound was applied to all the components of the freshly mixed mortar, i.e. water, PC and fine aggregates. In the second approach, PC slurry was first prepared using water and cement and ultrasonication was subsequently applied to the cement slurry. Finally, the fine aggregates were added during the final stages of mixing to obtain mortars with sonicated paste. The results indicated an enhancement in the evolution of chemical shrinkage when both 26 and 132 kHz frequencies were applied to the cement paste for a duration of 2 minutes. Cement pastes sonicated at 26 kHz for 2 minutes showed a slightly higher rate of chemical shrinkage than those treated at 132 kHz for the same irradiation time. Similarly, the corresponding mortars yielded a higher rate of development for both compressive and flexural strengths when subjected to a higher acoustic intensity at 26 kHz over 91 days curing in water, than those treated by a gentler insonation at 132 kHz. The application of PUS to fresh mortar mixes reduced the strengths of hardened cement mortars at 1 day compared to the non-sonicated mortar. In this regard, the effect of ultrasound with a higher intensity at 26 kHz is more profound than PUS at 132 kHz. However, at later ages, the mortars treated at 26 kHz acquired a higher compressive and flexural strength than either those treated at 132 kHz or the control samples. Longer exposure of PUS at 26 kHz considerably enhanced 1-day strength that could be related to the deaeration effect of ultrasound on the partial removal of entrapped air in fresh mortar. The addition of aggregates to the ultrasonicated paste was found to lead to a considerably significant improvement in the flexural strength of the mortars, potentially indicating the modification of the bulk cement paste and the ITZ. These effects were supported by microstructural analyses of the hardened PC mortars fracture surfaces, using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) techniques. The present research concludes that the application of PUS in general has positive effects on the extent of cement paste hydration and then mechanical properties of mortar when a higher power density is used. Furthermore, the observations made for the first time in this work strengthen the position that ultrasound could be a promising technique to enhance ternesite hydration in ternesite-rich belitic calcium sulphoaluminate cements, as a novel low-carbon binder and an alternative to PC. This will be further investigated in a post-doctoral programme.

The stiffness and shear force capacity of Timber Concrete Composite (TCC) structures in flexure depend significantly on the connection between the two materials. This work was carried out due to some limitations found in Eurocode 5 (EC5) and existing predictive strength and slip modulus models of screw connections. One deficiency seen in these models is the neglect of consideration of the local characteristics of the screw embedded within the concrete on the behaviour of the connection between the timber and concrete. In addition, while Eurocode 5 currently gives guidance for evaluation of the shear force capacity of timber-timber connections, no guidance is available for timber-concrete connections in the code. Reviews have been made on the existing model of shear force capacity and stiffness. It was found that there was no research done on developing the shear force capacity and stiffness model based on the X-formation screw and considering variety in screw angle between 0° to 90°.Therefore a set of experimental tests on Timber-Concrete Composite structures was performed to investigate the effect of the screw angle on the effective length of the screw which also influences the embedment strength of the screw embedded within the concrete. In the experimental tests, strains were measured along the screw length embedded within the concrete for a number of double shear test specimens. The strain data obtained from the double shear tests were used to develop local bending moment curves along the screw embedded within the concrete. A strip analysis method was used across the screw diameter to determine the internal forces in every strip. The summation of internal moment across the screw diameter produced the local bending moment at point the strain gauges were located. Then the distribution of bending moments along the screw was produced by interpolating the moments at the gauged locations. From the plot of bending moment along the screw embedded within the concrete, the load distribution was obtained by double differentiating the moment curves. Displacement profiles were also produced by double integrating the moment curves. The plot of bending moment and displacement generated from strain gauges method then compared with scans of the actual screw shapes at the end of the tests. The screws were taking out of the tested specimen as careful as possible to avoid changing the screw shape. A scanner recorded the coordinates of the screw and translated them into a 2D data set. By analysing the 2D data from the screw scans it was possible to determine the screw curvature. From the curvature the local bending moment was calculated then the distribution of moment along the screw embedded within the concrete at the end of the test was produced. Comparison was made between the bending moment distribution and displacement generated by the strain gauges and the scanning, and the two methods showed very good agreement. The very useful parameter obtained from bending moment distribution from both methods was the distance of hinge from the interface between timber and concrete. This parameter was used in analysis of multiple linear regression to develop shear force capacity and stiffness model. After new model of shear force capacity and stiffness successfully developed, comparison was made with the suggested formulae from published model.

Rainfall-induced landslides occur extensively across the mountainous terrain of Nepal during the monsoon. Anthropogenic factors such as slope cutting for local road construction has been reported to have further aggravated the risk of rainfall-induced landsliding in Nepal. Although roads are vital infrastructure for development, the increased rate of landsliding due to road construction has reversed the anticipated benefits from improved road access. For the prevention and mitigation of such landslides, it is imperative to assess how the two key factors- road and rainfall interact to cause landslides. This study aims to better understand this interaction by conducting research that integrates reconnaissance surveys, in-situ tests, laboratory testing, field monitoring and numerical modelling using concepts of unsaturated soil mechanics. In this study, reconnaissance surveys were conducted along a newly widened local road (Daklang-Listi) in Sindhupalchok, Nepal to identify the issues related to local road construction that are conducive to landsliding. The field observations revealed that the non-engineered road widening involving slope cutting at steep angles without suitable slope protection, drainage and control over spoil disposal increased the susceptibility to rainfall-induced landsliding. For the investigation of the physical process of landsliding caused by the road-rainfall interaction using numerical modelling, the scope of this study was narrowed down to a case study of Kanglang landslide which occurred during the monsoon in July 2018 after road widening. In-situ testing and trial pit excavations were undertaken for the evaluation of subsoil conditions and for soil sampling at the selected location. Laboratory testing was performed to determine the physical, mechanical and hydraulic properties of the soil samples. To understand the hydrologic response of the soil during atmospheric drying and wetting, a field-monitoring station was installed near the Kanglang landslide, which consisted of a rain gauge, 10HS water content sensors and a data logger. The temporal variation of volumetric water content due to soil-atmospheric interaction was evaluated and the factors influencing the volumetric water content response were identified. The monitored data showed that the progressive wetting of soil during wet periods could lead to soil approaching saturation at shallow depths, which can reduce the soil suction and ultimately cause shallow slope failures. A back-analysis of the Kanglang landslide was performed using fully coupled flow-deformation analysis and safety analysis in PLAXIS 2D to evaluate the effect of the road cut and rainfall on the failure mechanism. Before the back-analysis, the numerical model was calibrated against the field-measured volumetric water contents. The calibration results confirmed that the model was capable of capturing the in-situ changes in soil water content due to infiltration and drying. The back-analysis results demonstrated that the ingress of rainwater caused a reduction of soil suction at shallow depths and the presence of the road cut promoted the failure leading to accelerated displacements at the road cut. To reinforce this observation, the back-analysis was replicated in a model without a road cut. The results of this analysis showed that the presence of the road cut decreases the initial factor of safety, thereby, increasing the susceptibility to failure. In addition, it was also demonstrated that the rainfall event that triggered the Kanglang landslide would not have triggered a failure in the absence of the road cut, hence, confirming that the presence of road cut in the hillslopes can be detrimental to slope stability during rainfall.

This thesis proposes an Inverse Discrete Choice Modelling (IDCM) framework for the enrichment of socio-demographic information for anonymous big datasets with predicable and interpretable enrichment performance. By addressing the research gaps in existing socio-demographic enrichment methods which fail to account for the underpinning microeconomic behaviour theory, the IDCM framework is applicable to and transferable between any enrichment contexts where behaviours of respondents can be obtained, and the socio-demographic information of the data is necessary yet unavailable. Specifically, the IDCM approach postulates that a discrete choice model (DCM) which characterise the dependence between the socio-demographic attributes of people and their behaviour patterns can be inverted to estimate the explanatory socio-demographic information. Correspondingly, the IDCM performance theory expresses the enrichment performance of the IDCM approach as a function of the assumed recalibrated constant. Moreover, the IDCM performance theory establishes the link between the estimated enrichment performance and a developed metric of enrichment efficiency using the assumed re-calibrated constant as a pivot, so as to characterise the variation in its enrichment performance due to changes in the data condition of the enriched sample. Two empirical applications are conducted to validate the ability of the IDCM performance theory to forecast and interpret the IDCM enrichment performance in light of various data conditions. Whereas the IDCM approach performs comparably to logistic regression and support vector machines, the proven ability of the IDCM performance theory in the comparative analysis against the two supervised machine learning methods acknowledges the transferability of the IDCM framework.

The purpose of this research study is to develop a methodological framework for the multi-hazard vulnerability assessment of unreinforced masonry structures (URMs) undergoing seismic, flood and wind loading. To date, the two main challenges related to multi-hazard vulnerability assessment are 1) the substantial discrepancy in the level of advancement of single-hazard vulnerability assessment procedures, specifically in relation to the complexity of analytical model used to correlate the level of damage caused to buildings to the hazard component and 2) the conceptual differences in the definition of single-hazard fragility curves to be used to conduct multi-hazard damage assessment in a commensurate manner. Therefore, research effort is still required to develop a harmonized analytical model able to relate the behaviour of masonry structures subjected to earthquake, flood and wind hazard to the corresponding levels of damage to unreinforced masonry structures, to define a common structural parameter for the derivation of single-hazard fragility functions which also allow for damage comparisons between these distinct perils. The framework proposed in this work carries out the assessment at a wall level. The hazard and the exposure components of the vulnerability assessment procedure are taken as inputs for the development of a kinematic model based on revised Yield Line Theory concepts. The main elements of added novelty are the inclusion of the contribution of torsional effects generated at unit level caused by the application of horizontal loadings, and a more refined computation of the crack pattern, defined on the basis of the geometry of the wall and the geometry of the units. Given that several configurations of admissible crack patterns can be identified for the same wall layout subjected to horizontal loading, an optimization routine is built to find, by means of Limit State Analysis, the minimum load required to produce failure corresponding to a specific crack pattern, and the maximum value of the performance variable, defined as the ratio between the demand imposed by the loading and the capacity of the system itself, for the collapse limit state. Such parameter, representative of the strength capacity of the system is then used to derive single-hazard fragility function to conduct collapse assessment. These curves are extracted by considering the variability of the asset, and hence focus on the aleatory aspect of the exposure component, rather than considering the uncertainties associated with each of the hazard's intensity measure. The variance considered includes geometry, materials, presence of opening and boundary conditions. Comparisons on resulting fragility functions are drawn across seismic, flood and wind hazard, to establish relevance of the above parameters and sensitivity of the fragility functions. The framework is applied to the case study area of the Philippines, to prove the feasibility of the approach proposed.

This thesis presents analysis methods designed to rapidly estimate the load-carrying capacity of backfilled masonry arches. To help engineers to analyse backfilled masonry arches, various methods exist. However, some of these are over-simplified; others are in contrast very complicated and time consuming for engineers to master. In industry simple, accurate, and rapid methods are potentially very useful. Thus the development of such methods has been the main focus of this thesis. One available numerical strategy is computational limit analysis. Limit analysis is a method that can obtain the failure load without the need to carry out an iterative elastic-plastic analysis. Limit analysis theorems are employed to obtain upper- and lower-bounds on the collapse load. Discontinuity layout optimization (DLO) is a limit analysis procedure that can be used to determine the critical layout of discontinuities and associated upper-bound limit load for plane plasticity problems. However, the computational cost of DLO can be quite high. In order to address this, a fast running DLO procedure is proposed. For lower-bound analysis, a soil-fill stress field model is proposed. In this model the Mohr-Coulomb criterion is strictly obeyed in the stress field in the backfilled masonry arches. Both literature benchmark problems and backfilled masonry arch bridge problems are solved to show the efficacy of the upper- and lower-bound methods. Another strategy is limit equilibrium. The limit equilibrium method has been used to obtain approximate solutions for stability problems. The method is usually considered as an approximate means of constructing a slip-line field. Differential planar soil elements are proposed here to simulate concave or convex arching effects in the retained soil backfill around arch barrels. An anisotropic stress distribution is applied to model the backfill material that in reality is often heterogeneous in nature. In this method, equilibrium considerations can be used to solve the masonry arch bridge problems by simple static methods. A number of examples from the literature and industry are analysed to demonstrate the efficacy of the limit equilibrium method. The choice of method is dependent on the principal goal of the assessment. To balance degree of accuracy and computational cost, the proposed rapid analysis strategies have been designed to provide a simple and fast means of assessing bridge load-carrying capacity. The upper- and lower-bound strategies provide rigorous solutions, but sometimes underestimate the bridge load-carrying capacity especially of the weak backfill strength. The limit equilibrium strategy provides approximate solutions which could address this issue.

The use of supplementary cementitious materials (SCMs) offers a viable solution to partially substitute Portland cement and reduce carbon emissions associated with cement production. However, concerns over the future availability of traditional SCM sources, such as fly ash and slag, have left the concrete industry in need of alternatives. Water treatment plants generate large volumes of waste alumina-rich sludge in the purification of water for potable supplies. In the UK, the commonly used long-term disposal method is landfilling but this is being actively discouraged due to limited landfill spaces and increasing landfill costs. To address this disposal challenge and the need for alternative sources of SCMs, this thesis assesses the suitability of alum sludge as an additive in cement. A clear understanding of the physical and chemical impact of binder materials is fundamental to predicting performance and durability. Consequently, this work investigates the physical, chemical, and mineralogical properties of alum sludge and its calcination products, and their impact on the hydration, phase assemblage, microstructural development and engineering performance of blended cements. Alum sludge was calcined at 475-1100oC and then characterized to correlate thermal changes with cementitious activity and engineering performance. Alum sludge calcined at 825oC transforms to poorly crystalline η-alumina (eta) and has the best cementitious activity. It is found that the reactivity of the sludge leads to the massive precipitation of ettringite at very early age which impairs the ability of gypsum to control C3A hydration leading to an undersulfated cement which inhibits alite hydration. The poorly crystalline η-alumina is metastable, transforming to highly crystalline -alumina (alpha) at 1100oC, whereupon alite hydration is enhanced because undersulfation is avoided and the alumina provides nucleation sites, leading to improved performance. The results obtained highlight the main properties of calcined sludge, explaining their influence on calcined sludge reactivity, cement hydration and the microstructure of the matrix. Synergistic interactions of calcined sludge in blended cements containing slag (amorphous silicon oxide source) and/or limestone (calcium carbonate source) were explored. Results show that coupled substitutions of slag and calcined sludge (at 825oC) also resulted in an undersulfated condition due to reduction of gypsum contained in PC and the increased Al3+ concentration contributed by both slag and sludge leading to significant inhibition of alite hydration. Consequently, slag hydration was also hindered, leading to further reduction in performance. However, a synergistic interaction between limestone and η-alumina from sludge calcined at 825oC was confirmed. Calcined sludge provides aluminates, increasing the aluminate-sulfate ratio and enhancing limestone reaction. This reaction leads to the formation of mono- or hemicarboaluminate hydrates instead of monosulfoaluminate hydrate and stabilizes ettringite, leading to enhanced mechanical strength. This synergistic effect produced comparable strength to neat PC within 7 days with Strength Activity Indices up to ~98%. The lower pH of calcined sludge favoured limestone dissolution which enhanced Al3+ reaction, which is limited by gypsum dissolution in the absence of limestone. Hence, with an increase in the calcined sludge content, the chemically reactive portion of limestone increased. However, the degree of alite hydration decreased and undersulfation was evident at higher doses of calcined sludge. At later ages, the hydration of clinker phases in the neat PC system progresses at a faster rate leading to slightly lower Strength Activity Indices in the ternary calcined sludge-limestone cements. The findings of this study show that clinker hydration and mechanical strength are strongly influenced by Al2O3/SO3 ratio in the calcined sludge-blended cements. To avoid an undersulfated condition, it is proposed that optimal doses of gypsum and limestone powder can help control the accelerator effect of 825oC sludge on C3A hydration while exploiting reaction synergies with limestone. In this way, the higher reactivity of the 825oC sludge can be better utilized for improved performance. This study provides a fundamental base and a promising direction for further studies and the widespread utilisation of calcined alum sludge in the cement industry.

The use of fibre reinforced polymer (FRP) reinforcement as an alternative to conventional steel rebars has attracted increasing interest as a promising alternative for reinforced concrete, as the FRP reinforcement bars are not susceptible to corrosion and are more durable, lightweight, and environmentally friendly than steel. Increasing attention is being paid to understand and improve the performance of FRP reinforced concrete members under serviceability conditions with a particular focus on the avoidance of excessive deformations and crack widths. Moreover, the introduction of fibres in fibre-reinforced concrete (FRC) improves the flexural toughness and cracking capacity of the material. Synthetic fibres, as opposed to steel fibres, have a lower carbon footprint but also a lower modulus of elasticity. This, added to the fact that most previous research on the structural performance of FRC has concentrated on metallic fibres, made it necessary to study their contribution towards the improvement of flexural and cracking performance, particularly in the long-term under sustained loads.

This study aimed to investigate links between contractual disputes and project cultures in the construction industry of Saudi Arabia. Contractual disputes are those that arise from the contractual relationships binding parties to a particular project, which may broadly be categorised as being between an employer/client and a contractor or between a main contractor and a subcontractor/supplier. Project cultures describe the values, principles, beliefs and behaviours that parties bring into a contractual agreement. For this thesis, the author explored the extent to which the local culture of Saudi Arabia shaped and influenced contractual construction project disputes. The idea was to deepen the current understanding of the role that culture plays in the evolution of project disputes and that the study would explore the role that arbitration plays in the resolution of disputes on construction projects. Specific objectives provided a framework for the investigation, which included a systematic review of academic literature to assess current levels of understanding about construction industry culture and how it is linked to the evolution of disputes on construction projects. That review also assessed systems used to resolve construction disputes, focusing on arbitration and the arbitration system used in Saudi Arabia. In Saudi Arabia, there was a gap in research investigating links between the local construction industry culture, disputes and the arbitration process to resolve disputes. This research aimed to fill that gap and reveal the extent to which the local culture facilitated either amicable or litigious dispute resolution methods. The author compiled data about construction industry disputes in Saudi Arabia to draw lessons linked to the overall project aim using case studies, observation, a questionnaire survey and face-to-face interviews. Analysis of the data followed a grounded theory-based critical post-positivist approach, which enabled the author to reveal new insights about disputes, arbitration and cultures in the construction industry of Saudi Arabia. The research was able to add insights about common causes of disputes, with time overruns and awards to the lowest tender often being cited as a main cause of local disputes. One important and previously under-reported issue discovered by this research was that, in Saudi Arabia, the good-faith principle between the parties at the beginning of the project was a cultural issue that often led to disputes. That cultural issue often resulted in contracts being made with insufficient or inadequate contractual documentation. The poor development of contract documents then creating the seed from which disputes grew. The research was also able to reveal that people who work in the Saudi construction industry and who had little or no experience supported the view that disputes will be resolved amicably. However, as more significant experience is gained, so that early optimism diminished. That finding reveals how the local construction culture is less open to amicable means of dispute resolution. To counter the hardening of attitudes towards amicable dispute resolution methods within experienced construction industry practitioners, the author questioned if the arbitration process could be a tool to affect a cultural change. In that regard, the research revealed that the transparency of the process, the high level of cooperation between parties, and heightened communication levels between the disputants were found to be strong points about arbitration in Saudi Arabia. However, those benefits are realised if the parties to construction projects in Saudi Arabia actively engage with the arbitration process. The latter point is a real problem, as this research also discovered that low levels of awareness and understanding of the arbitration process and its effectiveness were weaknesses of the current system in Saudi Arabia. On a positive note, the research also found that awareness levels were growing, with increasing numbers of organisations including arbitration clauses in their contracts. Overall, research has been able to make a positive contribution to knowledge and understanding of links between contractual disputes and project cultures in the construction industry of Saudi Arabia. The findings are timely, as the research found signs that employers in Saudi Arabia are beginning to recognise the importance of cultural awareness and have started to provide culture training for their employees. However, when working to resolve disputes in the country, cultural awareness has yet to impact the level of cooperation between the parties when working to resolve disputes. To help facilitate future cultural change, the author has concluded this research with insights about features of the culture in the construction industry of Saudi Arabia that both help and hinder the way that disputes arise and are resolved in the country.

This research focuses on the investigation of delamination assessment in composite structures by using methods based on structural dynamic responses. Delamination is a common type of damages for composite structures in applications. It is necessary to detect and assess the delamination in composite structures to ensure the composite structures operating and maintaining. However, the dynamic responses of structures with delamination may be difficult to be analyzed due to the complexity of composite structures as the result of the different properties of materials in the composite structures. Therefore, it is necessary to develop effective methods for delamination analysis and assessment, which will be investigated in this research. To address these problems, this research aims to: 1. Develop new methodologies for dynamic analysis of delaminated composite structures to analyze the effect of delamination based on the evaluation of the vibration characteristics of composite structures with different delamination configuration; 2. Develop effective methodologies to detect and assess delamination in composite structures based on the dynamic responses by using the phase space topology analysis to improve the sensitivity and robustness of delamination assessment for composites structures; To achieve these two aims, the research content and novelty are stated as: 1) Firstly, this study proposes a method based on the Green's function to develop analytical models of delaminated structures that can be used to investigate the effect generated by delamination on the vibration characteristics. The accuracy of this developed model to describe the vibration characteristics of delaminated beam structures especially under forced excitation is verified by the comparison with other types of models, including the numerical models. The result demonstrates the accuracy and advantages of the proposed analytical model to investigate the effect of delamination on the vibration characteristics of the beam structures under excitation of various frequencies with different delamination configurations, such as size, location, and depth. It should also be noted that the proposed modeling method is demonstrated useful to investigate the vibration characteristics of various measurement locations, which is important for the delamination assessment based on the dynamic responses of structures. 2) Secondly, based on the developed analytical model by using the Green's function, the investigation has been done for the effect of various measurement locations on the sensitivity to the particular vibration modes with various delamination configurations. Based on this situation, the methodology based on the modal observability (Mn) and the spatial observability (So) is proposed to optimize the structural sensor locations to make the measurement focusing on the vibration modes sensitive to the delamination, which can improve the delamination assessment. The result demonstrates that the proposed methodology is effective to determine the sensor locations which can provide strong signals with sufficient distributions of the particular vibration modes sensitive to the delamination. So the optimization can improve the delamination assessment effectively based on providing sensitive vibration measurement locations. 3) Thirdly, a methodology based on the phase space topology analysis of the dynamic signals measured from the structures is proposed to assess delamination in composite structures. The phase space topology structures are evaluated by using a method named phase space reconstructed (PSR) method based on the dynamic signals measured by the dynamic sensors. A feature named the change of phase space topology (CPST) is used to describe the effect of delamination on the phase space topology structures. The result demonstrated that the phase space topology structures and CPST are sensitive to delamination. The robustness of the proposed feature to the measured noise has also been tested, which shows that the proposed method and feature have sufficient robustness to the measured noise in applications. This research also improves the methodology to assess delamination based on the phase space topology analysis by incorporating with the wavelet packet decomposition. The wavelet packet method can decompose a dynamic signal into several sub-signals in different frequency ranges, which may contain different local information relevant to the delamination. Then the phase space topology structures and the CPSTs of different sub-signals can be evaluated and investigated to analyze the local information. The phase space topology structures of sub-signals decomposed by the wavelet packet method can describe the change of energy distribution of sub-signals in different frequency ranges generated by the delamination. The possibility of the proposed method is demonstrated by the simulation and experiment and the proposed features will be used in the following work; 4) Based on the previous work, a method by using the artificial neural network (ANN) based on the phase space topology analysis to estimate delamination in structures is proposed tested. The ANN can be used to describe the relationship between the delamination and vibration characteristics to estimate the delamination without mechanism analysis for composite structures. The CPSTs of original signals and sub-signals decomposed by the wavelet packet method are used as input factors for the ANN to assess the delamination in composite structures. The accuracy of the ANN for the delamination assessment can be enhanced by training the ANN with more cases. The possibility and the potential are tested in this research. The different performances for various delamination parameters estimate are also analyzed, which shows that the performance for various delamination parameter assessments is different due to the different effect of delamination on the input factors. Furthermore, the performance of delamination assessment by using the ANN with different input factors is investigated to analyze the effect of input factors on the delamination assessment performance and find the best input factors for ANN in this research. The results show the CPSTs of sub-signals generated by wavelet packet decomposition are the best input factors because this type of feature can provide more information with high sensitivity and good robustness to the measurement noise. In conclusion, this research will provide a systematic study for the improvement of delamination assessment and development of applicable methods for composite structures based on the dynamic signals by analyzing the phase space topology structures combined with wavelet packet decomposition and ANN. Moreover, the theoretical analysis and optimization for dynamic signal measurement are analyzed to provide explanation and support for the delamination assessment. The potential of the proposed methods for other types of damage in composite structures and other applications are also mentioned in this research.

Laminated composite structures have been increasingly used in engineering structures due to the beneficial properties such as light weight, high stiffness-to-weight ratio, high strength-to-weight ratio and design flexibility. Understanding the vibration behaviour of composite structures is of vital importance to achieve optimal structural design with excellent dynamic performance in terms of low vibration and noise level. However, because of the complexity in modelling and simulation, the vibration energy flow behaviour of laminated composite structure remains largely unexplored and needs detailed investigations. The vibration power flow analysis (PFA) approach is a widely accepted technique to characterize the dynamic behaviour of complex structures. It has been extensively used for vibration analysis of metallic structures, but not of composite materials. This thesis aims to develop effective vibration power flow analysis methods for laminated composite structures to reveal its dynamic behaviour and vibration energy transmission characteristics. PFA based on analytical and numerical finite element methods is carried out to determine the vibration energy input, dissipation, and transmission of composite structures subjected to external excitation force. Both constant stiffness laminated composite (CSLC) plates with straight fibres and variable stiffness laminated composite (VSLC) plates with curvilinear fibres are considered. It is shown that the fibre orientations and stacking sequences have significant effects on the power flow characteristics and dominant vibration transmission paths. For the coupled system such as plates attached with passive devices and coupled L-shaped composite plates, a substructure approach based on analytical and numerical methods is employed to obtain steady-state dynamic response and vibration power flow variables. It is demonstrated that novel inerter-based suppression devices can be attached to the composite plate to modify its vibration transmission and suppress vibration level according to specific design requirements. The fibre orientations of the single or coupled composite plates can be tailored for desirable energy transmission paths. The work described in this thesis reveals that structural design and optimization of composite structures with enhanced vibration suppression performance can be achieved based on vibration energy flow and transmission behaviour. These findings provide new insights for the enhanced dynamic designs of laminated composite plates by tailoring fibre orientations and the suppression of their vibration using inerter-based passive devices. This thesis yields an improved understanding of power flow behaviour of composite structures.

Evidence suggests that trees and forests around the world are constantly being threatened by disease and environmental pressures. Over the last decade, new pathogens spread rapidly in European forests, and quarantine measures have mostly been unable to contain outbreaks. As a result, millions of trees were infected, and many of these have already died. It is therefore vital to identify infected trees in order to track, control and prevent disease spread. In addressing these challenges, the available methods often include cutting of branches and trees or incremental coring of trees. However, not only do the tree itself and its surrounding environment suffer from these methods, but they also are costly, laborious and time-consuming. In recent years the application of non-invasive testing techniques has been accepted and valued in this particular area. Given its flexibility, rapidity of data collection and cost-efficiency, Ground Penetrating Radar (GPR) has been increasingly used in this specific area of research. Consequently, this PhD Thesis aims at addressing a major challenge within the context of early identification of tree decay and tree disease control using GPR. In more detail, two main topics are addressed, namely the characterisation of the internal structure of tree trunks, and the assessment of tree root systems' architecture. As a result, a comprehensive methodology for the assessment of both tree trunks and roots using GPR is presented, which includes the implementation of novel algorithms and GPR signal processing approaches for the characterisation of tree trunks' internal structure and the three-dimensional mapping of tree root systems. Results of this research project were promising and will contribute towards the establishment of novel tree evaluation approaches.

Electrical Impedance Tomography (EIT) is an imaging method that works by reconstructing a distribution of the electrical conductivity of an object from voltage measurements taken on the object surface. In cases where conductivity variations can be reliably correlated with types of feature, the conductivity distribution gives a good idea of what is inside the object. Concrete is a near-ubiquitous building material and its production accounts for a substantial proportion of global CO2 emissions. By improving the resilience of concrete to deterioration and finding methods for assessing the risks posed by cracking and damage, the amount of wasted concrete and thus CO2 emissions can be reduced. This project was aimed at developing EIT techniques for the practical problem of imaging of voids and cracks in concrete, to provide a means for assessing those risks as well as for validating the performance of self-healing concrete. Matured concrete is a good insulator of electricity and applying EIT to it without high-voltage equipment is very difficult. This project investigated the creation of less resistive concrete by adding conductive additions to mortars, and a methodology for applying EIT to this less resistive mortar was developed. A lot of development remains before EIT can be accepted as a method for assessment of in-use structures, but this work will be of use for anyone attempting to apply EIT to concrete and cementitious materials, as well as reducing the resistivity of those materials.

This dissertation attempts to advance empirical ground-motion modelling methodologies by considering spatial and cross-intensity measure (IM) correlation properties. Despite the recent advancements in empirical ground-motion models (GMMs), there are some limitations in the current state-of-practice for their development, including (1) statistically inefficient approaches for estimating the model parameters; and (2) the ad hoc consideration of spatial correlation properties rather than an integrated procedure within the model development process. This dissertation addresses these two issues through the statistical proof and numerical implementation of a one-stage estimation algorithm to establish GMMs, considering the spatial correlation component in an explicit and integrated fashion. The proposed algorithm is numerically efficient in estimating model parameters and is extendable to address anisotropy and nonstationary spatial correlation properties. Utilising the proposed algorithm, this dissertation proposes new GMMs with spatial correlation for IMs representing the amplitude, cumulative measures, energy content, and inelastic spectral displacement. The focus is on Italian strong-motion records. The cross-IM correlation models between the considered IMs are also established. The developed GMMs and the obtained correlation properties are scrutinised and compared with the available models in the literature. The differences in terms of model development methodologies and the underlying datasets, which collectively affect the results obtained from the developed GMMs, are critically discussed. Different application cases are finally presented demonstrating the values of the developed methodology and the resulting GMMs for providing accurate ground motion estimates for the purpose of seismic hazard analysis.

Alkali-activated fly ash-slag (AAFS) concrete manufactured through the reaction of alkaline activator with industrial aluminosilicate by-products (fly ash and slag) is considered as a promising alternative to Portland cement (PC) concrete because of its environmental benefits (e.g. low CO2 emission and low consumption of natural resources) and superior engineering properties under ambient curing condition. There is about 55% less CO2 emissions in the production of AAFS comparing with the production of PC concrete. In addition, AAFS concrete can achieve a good synergy between fresh properties, mechanical properties and durability under ambient curing which cannot be achieved by the sole alkali-activated concrete, e.g., alkali-activated fly ash (AAF) and alkali-activated slag (AAS). AAF needs to be cured under an elevated temperature (60 ~ 85 °C) to gain early-age strength, whereas AAS concrete has some drawbacks including poor workability and quick setting. The mechanical properties of AAFS concrete are highly dependent on its heterogeneous microstructure with multiscale (nano- to macro-scale) and multiphase (pore, reaction products, unreacted fly ash and slag particles, and aggregate). Although the microstructure and mechanical properties of AAFS concrete have been studied for decades, a systematic understanding of the microstructure and micromechanical properties of individual phases within AAFS concrete and their corresponding relationships with the macroscopic mechanical properties is still lacking to date. More specifically, the following aspects for AAFS concrete have not been fully understood: (i) reaction mechanism of fly ash and slag particles in AAFS system; (ii) microstructure evolution of interfacial transition zone (ITZ) in AAFS concrete; (iii) multiscale micromechanical properties of AAFS concrete; (iv) multiscale microstructure-mechanical properties relationship in AAFS concrete. To fill these research gaps, this thesis aims to systematically characterise the microstructure and mechanical properties of AAFS concrete cured at ambient temperature at multiscale from nano- to macro-scale and to investigate the microstructure-mechanical properties relationship in AAFS concrete in depth. The multiscale features of AAFS concrete are identified based on four length levels: Level 0 (solid gel particle: 1 nm ~ 10 nm), Level I (gel matrix: 10 nm ~ 1 µm), Level II (paste: 1 µm ~ 100 µm), and Level III (concrete: 1 mm ~ 10 cm). Regarding the multiscale characterisation of microstructure, the nanostructure of solid gel particle at Level 0 is characterised using nuclear magnetic resonance (NMR), while the chemical composition of gel matrix at Level I is evaluated by means of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The in-situ monitoring of microstructure evolution of fly ash and slag particles in AAFS paste at Level II is achieved using X-ray microcomputed tomography (XCT), providing new insights into their reaction mechanism. The microstructure evolution of ITZ in AAFS concrete at Level III is characterised using backscattered scanning electron microscopy (BSEM) and energy dispersive spectrometry (EDS), which delivers needed insight into the mechanism of ITZ evolution. The results of microstructural characterisation provide a systematic understanding of the microstructure of individual phases in AAFS concrete and their inherent relationships at different length scales. With respect to the multiscale characterisation of micromechanical properties, nanoindentation is used to evaluate the micromechanical properties (elastic modulus and hardness) of individual phases at Level I. It is the smallest material length scale that can be measured through experimental tests. The effective mechanical properties of AAFS paste at Level II are estimated using the self-consistent continuum micromechanics model by assuming that each nanoindentation test serves for a single phase in the material. Afterwards, the micromechanical properties of ITZ in AAFS concrete at Level III are evaluated through a series of statistical analysis. The multiscale micromechanical analysis offers the first-hand information of micromechanical properties of different phases in AAFS concrete and their contributions to the macroscopic mechanical properties of AAFS concrete. Lastly, the relationships between chemistry, microstructure, and mechanical properties of AAFS concrete from Level 0 to Level III are established based on the experimental results obtained above, which enable us to better understand the development of overall mechanical properties of this new type of concrete. The experimental and simulated results indicate that the dissolutions of fly ash and slag particles in AAFS system are not uniform due to their inherently heterogeneous characteristics, which would consequently lead to the formation of non-uniform reaction products, mostly accumulating within the boundary of the original particles. The polymerisation degree and cross-linking of reaction products are improved over curing age, potentially through the initial formation of C-A-S-H gels followed by the gradual development of N-A-S-H and N-C-A-S-H gels with a higher cross-linking degree. Within these three types of reaction products, the N-A-S-H gels have a relatively low elastic modulus due to their high level of structural disorder and gel porosity. In addition, it is found that the elasticity of reaction products and their relative volumetric proportions mainly determine the macroscopic elasticity of AAFS paste, while the porosity and pore size distribution primarily condition its macroscopic strength. Furthermore, it is also observed that ITZ formed in AAFS concrete has a comparable microstructure and micromechanical properties to the paste matrix, which indicates that ITZ might be not the weakest region within this new type of concrete. The ITZ with compact microstructure and high micromechanical properties would help to improve its macroscopic mechanical strength, especially for the fracture properties.

This PhD program aims to provide insights into the behaviour of tyre reinforced sand, and to further the understanding of the reinforcement mechanisms. The discrete element method (DEM) using the software PFC3D version 5.0, is used to investigate the micro- mechanics of tyre-reinforced sand based on pull-out tests. A series of numerical direct shear tests have been performed. A full investigation of the individual particle shape descriptors (e.g., elongation index, flatness index, convexity and roundness) is presented, highlighting their influence on the macroscopic behaviour (e.g., failure mode and volumetric response). MorphologI G3 at UCL helps to obtain the quantitative particle shape information on Fujian Standard Sand. The sand information is incorporated in the results of particle shape studies to propose a representative particle shape for Fujian Standard Sand to model direct shear tests, leading to the calibration of pure sand. Then, a new three-dimensional DEM model for tyre rubber is developed based on uniaxial tensile tests. The model can capture the key volume change characteristics of tyres with a Poisson's ratio of 0.5 independent of the tyre dimensions. Tyre rubber is modelled using body-centred-cubic (BCC) packing with linear inter-particle bonds. Next, a systematic parametric study is presented, which includes the effects of different packings, particle overlapping, particle radii and sample aspect ratios on the mechanical response of the tyre model using Young's modulus and Poisson's ratio. The DEM parameters are set to match corresponding experimental Young's modulus data, completing the calibration of tyre. Lastly, the tyre - sand interface coefficient friction is calibrated from numerical and laboratory interface direct shear tests. All DEM parameters are used in tyre reinforced sand pull-out tests simulations. Micro analyses (such as particle displacement, velocity, contact force) presented in simulations show that the DEM tyre-sand pullout test simulation can capture the progress failure of tyre rubber during the pull-out process, and the intrusive capabilities of the discrete element method are used to gain insight into the reinforcement mechanisms between tyre and sand.

Pipelines are an integral part of offshore infrastructure supporting the oil and gas industry and the consequences of their failure have severe economic and environmental ramifications. Changes in pipe internal pressures and temperatures from the as-laid condition to their operational state cause large thermal expansions. When axial strain from thermal expansion is resisted by the pipe-soil friction, the effective axial force in an unburied pipeline is relieved by lateral friction-sliding-buckling. The phenomenon of pipeline buckling is a significant challenge in managing the global stability of high pressure-high temperature offshore on-bottom pipelines. Pipelines are commonly given a protecting coating to aid in protection from damage and to provide thermal insulation. The use of polypropylene in this application is prevalent but relatively recent so correct quantification of the interface shear strength between marine sand soils and polypropylene is key to robust global stability design. Herein, an extensive campaign of soil and interface shearbox testing has been undertaken to determine and evaluate the shear response of polypropylene surfaces. Parameters such as soil grading, density, surface texture, stress level, and cyclic behaviour have been investigated. The results show that the efficiency of the interface is strongly dependant on the soil grading and the surface texture at the interface. The shear response of soils at the interface with smooth surfaces is bilinear, characterised by an initially linearly elastic response at very small horizontal displacements, that transitions rapidly to a near constant shear stress plateau. Surfaces with greater roughness provoke a dilatant soil shear response more typical of a soil-only behaviour. Greater magnitude of surface texture engenders greater dilation leading to greater peak shear strengths. A relationship has been developed which can aid designers in predicting interface friction for polypropylene surfaces and sandy soils given surface texture, soil grain size, and stress level input parameters. The application of the experimental results to real-world problems was investigated through numerical modelling in Abaqus of an approximately 5 km long pipe on a rigid seafloor using friction penalty and non-linear springs to model pipe-soil interaction and force-displacement response. The impact on global stability and buckling parameters of changes in pipe-soil friction and of applying a differential friction regime along the pipe was investigated. Numerical analysis results showed that such techniques are able to significantly change the distribution and magnitude of buckles.

This thesis aims to evaluate the effects of Structure-Soil-Structure Interaction (SSSI), by performing time-history seismic simulations, given different parameters of structures, inter-building spacings, and soil types. Different linear and nonlinear reduced-order models are generated and subjected to varied acceleration ground motions. An extended 2D linear model that enables higher mode interaction between structures is proposed (Chapter 3). Results suggest that the coupled effects are possible between more than just the primary modes. Therefore, there is a significant interaction between a small building closely flanked by a much taller one. Chapter 4 introduces a 2D model that examines the SSSI between unsymmetrical-plan and symmetrical-plan buildings. Results suggest that a taller torsionally-irregular building adjacent to smaller buildings could be adversely affected by SSSI. This contradicts previous studies, where the taller buildings benefit from adjacent smaller buildings. Nonlinear soil behaviour is incorporated in the two-dimension model (Chapter 5) by employing Bouc-Wen's model, for the soil underneath the foundations. The ground motion is spectrally matched with Eurocode-8 elastic spectra. Results show that the SSSI effects could be more pronounced when the nonlinear behaviour is considered. Chapter 6 presents a 3D model of SSSI between multiple buildings which shortens computational run-times for large clusters. The auto-rotational and inter-rotational spring stiffnesses of foundations are determined by a surficial displacement field (based on Boussinesq approximation and calibrated against FEA) and inverse system identification (using least-squares or Kronecker products). Different building arrangements are presented to compare with previous research and highlight the method's versatility. Chapter 7 investigates the effects of the rotational ground motions upon buildings. Rotational ground components are extracted by using a multi-station procedure, and data from the SMART-1 array are employed. Results show that the rotational ground motion can amplify the responses of certain structures, depending on the ratio of rotational to horizontal ground motions.

This thesis proposed a two-stage input-output system identification methodology to investigate the possibility of estimating the bridge modal parameters, i.e., natural frequencies, damping ratios, and modal masses, under excitation of a moving vehicle with the simultaneous use of the moving input acceleration signal and the measured bridge acceleration responses. In the first stage, which is an output-only identification problem, the bridge mode shapes are estimated from the measured bridge forced and free vibration acceleration responses only. The obtained estimated bridge mode shapes are then served as a modal basis to re-express the coupled bridge and vehicle geometric coordinates as decoupled modal coordinates. This procedure then leads us to the second stage identification. With both the input and output information for each mode, a series of (Frequency Response Functions) FRFs can be constructed by using the Discrete Fourier Transform (DFT) technique, along with the parametric model of the Accelerance for a linear system, an optimization procedure is performed to extract the natural frequencies, damping ratios, as well as the modal masses simultaneously. In order to verify the proposed method, a simply supported Euler-Bernoulli beam of known parameters is used as an example. Its responses to a moving load and a quarter car with the influence of the road roughness are calculated numerically, yielding simulated measured accelerations at a series of fixed locations on the structure. With these numerically generated data, the feasibility and efficacy of the proposed two-stage strategy are validated. A comparison work to examine the estimation accuracy and efficiency is conducted by using the free decay response of the bridge. To make the proposed method more general, both models, i.e., moving load and quarter car traversing the bridge, are nondimensionalised, and they are simulated with and without noise. Upon verifying the proposed method, we discussed the impact factors, which can influence the estimation results. We discovered that the nondimensionalised spatial frequency is the most important one, which, if known beforehand, can give guidance to the identification results. Apart from the nondimensionalised spatial frequency, we recognised that the mode shapes estimated from the first stage are also an important factor that can influence the identification accuracy. Therefore, we proposed a new concept real-valued one-sided spectral density matrix, which not only gives the same level of accuracy for the estimated natural frequencies and the damping ratios but also generates better mode shape estimation compared to the classical complex-valued two-sided spectral density matrix. This new approach is used throughout this study to give a better estimation of the mode shapes. Notwithstanding that the proposed two-stage method is the main topic of this study, our research is far beyond the Vehicle-Bridge Interaction (VBI) analysis. One of the major contributions is made to the Frequency Domain Decomposition (FDD) technique, which serves as the output-only technique for the mode shape estimation in the first stage identification of the proposed method. We reinterpreted the FDD using the Principal Component Analysis (PCA) with a Periodogram-defined Power Spectral Density (PSD) estimator. With our new theory, the role of the singular values and singular vectors are better defined. And we conclude that the FDD is a good technique to be used to detect the presence of close modes. In order to apply the FDD to extract the bridge mode shapes from the vehicle-induced bridge vibration responses (i.e., nonstationary process) only, a simple case study is designed to assess its ability to deal with a similar kind of nonstationary random process. While analysing a PSD estimator, which is a positive semidefinite self-adjoint compact operator on a Hilbert space, we introduced the concepts of pure state and mixed states from the quantum mechanics and defined a density operator based on a PSD estimator. With a density operator, we can calculate the corresponding Von Neumann entropy or the purity condition. By plotting the entropy or purity of a density operator against the frequency line, we can obtain a different picture of the behaviour of a system that the FDD fails to provide when two modes are very closely spaced. Particularly, we found that this new picture is mainly affected by three influence factors, i.e., correlation relation between the mode shapes of the two modes, damping ratios of the system, and the measurement noise level, which in turn can affect our mode shape estimation results.

Over the past 20 years, winters in the UK have become milder with the odd harsh winter and with the drive to use low carbon cements, questions have arisen over the performance of these concretes in freeze-thaw environments. This research project investigated the influence of cement type on concretes subjected to freeze-thaw conditions and the correlation between the microstructural properties of concrete and freeze-thaw performance using the CEN/TS 12390-9. The test method based on SS 137244 with a temperature profile of +20±4°C to -20±2°C and the results were compared to a scaling loss of up to 1.0 kg/m2 (deemed Acceptable performance). Concretes were manufactured with CEM I, CEM II/B-V (fly ash), CEM III/A (GGBS) and CEM II/A-L (limestone) cements, both non-air and air entrained, with different target strengths (20-60 MPa for non-air entrained and 20-50 MPa for air entrained) and a target air content of 4.5%, in accordance with BS 8500. BS EN 197-1 outlines the maximum addition contents that can be used in concretes and BS 8500 describes lower maximum limits for these additions regarding freeze-thaw conditions. CEM II/B-V (45%, 55% and 65%), CEM III/A (65%, 75%, and 85%) and CEM II/A-L (30%, 40% and 50%) were tested with addition contents higher than the allowable limits to determine how these influence the air void characteristics and freeze-thaw resistance. Concretes were analysed to determine the effects of air entrainment on the air void characteristics (air content of hardened concrete, spacing factor, specific surface, void frequency average chord length and microair content) and subsequent freeze-thaw resistance. The study also examined the effect of cement type in concretes with a range of target air contents (7.0%, 9.5% and 12.0%). Powers (1945) derived the Spacing Factor parameter to determine if a concrete could resist freeze-thaw whereby voids within the concrete were less than 250 μm apart. Development of 3rd generation superplasticizers combined with air entrainers, both air and non-air entrained concretes had a spacing factor value less than 250 μm (and for most concretes <100 μm), however many of the non-air entrained concretes did not achieve an Acceptable scaling rating showing that Spacing Factor cannot be used as an initial assessment of freeze-thaw resistance. Other parameters including the specific surface and void frequency should be considered when determining freeze-thaw resistance as these provide better correlation with performance. For non-air entrained concretes void frequency should be <0.600 mm-1 and where air entrainment is used, >0.600 mm-1 is acceptable. All air entrained concretes (target air content 4.5%) achieved an Acceptable scaling rating even with the varied cement type and target compressive strength. Non-air entrained concretes with a strength 40 MPa or less did not achieve this rating, and a 60 MPa CEM II/B-V concrete was not able to withstand freeze-thaw damage. Higher air contents were shown to protect the concretes, however there was a plateau point where the air entraining admixtures changes from increasing the air content to altering the workability like a superplasticizer but it did increase the freeze-thaw resistance with a maximum compressive strength loss of up to 25% for some cement types. Increasing the addition content above the maximum decreases the compressive strength. Despite the fact the compressive strength decreased with increased addition contents, the concretes were still able to achieve an Acceptable scaling rating. BS 8500 also states that a lightweight aggregate concrete can perform well in XF4 exposure conditions. This was studied to understand the microstructural properties and whether the aggregate replicates an air entrained concrete in terms of air void size and distribution, and to that end it was observed that lightweight aggregate results were like air entrained concrete. CEN/TS 12390-9 is based on the Swedish Standard 137244 for freeze-thaw resistance and compared to the UK, these temperatures are rarely seen. Different temperature ranges (+13°C to -13°C and +18°C to -8°C) were considered to reflect the temperatures more seen in the UK highlighting that for a concrete to be warmer (but still below 0°C) for longer, produced more scaling than CEN/TS 12390-9 temperature profile. Moreover, other environmental factors are not considered in the test including the effects of carbonation since concrete is exposed to carbon dioxide all year round then this can potentially influence a concrete’s resistance and found higher scaling loss for carbonated, non-air entrained concretes, in particular CEM II/B-V and CEM II/A-L concretes with a loss of 12.35 kg/m2 and 11.07 kg/m2 respectively. Increased salt concentration from multiple applications was studied to determine how increasing the salt levels (from the standard 3% to 6%, 9% and 12%) would affect the concrete’s durability. Observed was the change in freeze-thaw mechanism between 6% and 9% from surface scaling to internal freeze-thaw cracking.

Research into the seismic performance of structures with oil dampers have so far been driven primarily by the structural engineering community, with influential experimental work on the topic originating mainly from large scale shaking table testing of fixed-base prototype frames. Despite considerable advancements over the years in building complexity and realism into these test structures, little to no experimental effort has been made to investigate dynamic soil-structure interaction in such structures. Fixed-base shaking table testing of structures fitted with oil dampers confines energy dissipation to the supplemental damping devices alone, neglecting any contributions from foundation-soil inertial interaction that may arise in the field. A considerable portion of literature on oil dampers in structures emanates from a mathematical optimisation background, proposing computational algorithms to solve for optimal damper sizes and locations in a structure. Such iterative linear analysis is conducted in the frequency domain, and offers limited physical insight into the different facets of this complex nonlinear Soil-Structure Interaction (SSI) problem. Numerical and analytical work examining the effects of SSI on buildings with oil dampers have been limited in nature, often resorting to equivalent linear procedures to simplify the modelling of geometric and soil nonlinearities at the foundation-soil interface. This research seeks to address some of these limitations by pioneering the application of high gravity geotechnical centrifuge testing as a viable research tool to experimentally investigate dynamic SSI in buildings with oil dampers. Miniature oil dampers for use in small-scale model structures were developed for this purpose, following a series of trial-and-error experimentations. Sixteen centrifuge tests were conducted in total, each involving two similar 2-DOF linear elastic structures, one fitted with miniature oil dampers, and one left bare for comparison. Ground flexibility was varied between tests by changing frame base fixity conditions from fully rigid fixed base, to shallow embedment of raft foundations into dry dense and loose sand beds. Aspect ratios and foundation bearing pressures of the model structures were also varied to trigger different levels of SSI. Miniature accelerometers were used during the centrifuge tests to measure soil and structural accelerations, along with miniature load cells to track experimental oil damper hysteresis during shaking. The model frames were subjected to near resonant frequency sinusoidal excitations of different magnitudes to trigger different levels of SSI. The dynamic response of the structures to realistic multi-frequency component excitations was also recorded. Inter-storey oil dampers as tested in this study have delivered consistent improvements to the seismic response of structures for all of the input motions and ground conditions investigated in the centrifuge. It was found that additional viscous damping in the superstructure came at the expense of inertial interaction at its foundation-soil interface. The damped soil-structure systems were less sensitive to changes in ground conditions and foundation bearing pressures compared to their regular bare frame counterparts. Optimal oil damper control over structural accelerations and drifts was recorded for fixed base conditions, during weak excitations that did not trigger considerable resonance in the superstructures. Upon shallow embedment of the rafts into dry sand beds, reductions in damper control were reported, reaching minimal levels for the loose sand cases during moderate to strong near resonant frequency excitations. These reductions were not the result of subpar performance of the damped structures per se, but rather a consequence of the considerable improvement in the dynamic response of the regular frames being used as comparative benchmarks. If the foundation of a regular structure is permitted to rock during strong shaking, experimental evidence points to dynamic responses that are close to those expected from a similar structure fitted with oil dampers. However, such natural seismic mitigation measure was shown to be highly variable and unreliable for weaker excitations. Base flexibility and dynamic SSI did not have adverse consequences on the performance of structures fitted with oil dampers. While it is true that reductions in oil damper hysteresis were observed with reducing base fixity, this should not be interpreted as degradation in damper effectiveness. On the contrary, when excited close to resonance, the damped frames exhibited similar, albeit slightly lower, floor accelerations as base fixity was reduced. Estimation of the seismic input energy into a soil-structure system during near resonant frequency shaking showed both, damped and bare structures benefiting from natural rocking isolation; releasing the foundation rotational kinematic restraints lowers total energy going into the superstructures, causing the oil dampers in the frames to do less work. Even during SSI, the oil dampers continued to be the primary source of energy dissipation in the soil-structure systems. Lastly, the promising application of using nonlinear lumped-parameter structural models, with hyperbolic foundation moment-rotation backbone curves to predict centrifuge data, was demonstrated for the damped and regular bare structures. Such simplified models, solved in the time domain, offer a more elegant solution during early stage design compared to the response spectrum procedures currently advocated by published guidelines on the analysis of damped structures.

Shear strength of reinforced concrete beams significantly enhances when loads are applied closer to the support due to the arching action. This enhancement is widely investigated and has been included in the design codes. However, scarce resources are available in the literature regarding this enhancement for the case of multiple point loads applied within the enhancement zone; in addition, the available literature focuses on loads applied to the flexural compression face. Situations where multiple point loads are applied on the tension face are found in practice in structures like balanced-cantilever crosshead girders of bridges and transfer girders near the supports. Nevertheless, research considering this configuration has not been found in the available literature. The aim of this research is to study the effect of the loading arrangements on the shear strength enhancement of deep beams loaded on the compression or tension face with multiple point loads. This research was motivated by differences in the principal compressive stress trajectories obtained with nonlinear finite element analysis for the two different configurations. The author conducted an experimental program to investigate the influence of loading face, the effect of varying the ratio between loads applied within the enhancement zone and the influence on shear enhancement of partly loading the beam outside the enhancement zone. Detailed measurements of the crack kinematics and global deformation were obtained during the tests using the digital images correlation system. These measurements were used to provide descriptive models of the deformed beams and to evaluate the shear transfer actions of the tested beams. Strength of the tested beams was estimated using design codes (BS8110, EC2 2004 and MC2010) and non-linear finite element analysis. A novel practical strut-and-tie model was developed for the case of multiple point load applied to the tension face of the beams. This model correctly predicted the failure plane, fairly represented the stress field, and it is suitable for multiple loads applied entirely inside or partly outside the shear enhancement zone.

Soil-structure interface behaviour is an interesting topic due to the complexity of the interface mechanics. The interfaces between cohesionless soils and solid structure elements are encountered in different geotechnical engineering projects. The shear strength and stiffness characteristics, the thickness of the interfacial layer, the bonding and slipping properties are playing significant roles in an understanding the mechanical behaviour of such interfaces. One of the key parameters for the design and safety assessment of the engineering structures (e.g. retaining walls, deep and shallow foundations, tunnels and earth reinforcement) is the shear strength at the interface. Suction is an important stress-state variable of unsaturated soils. The magnitude of matric suction affects the shear strength and the volume change of soil and soil-concrete interfaces, thus the adequate characterization of interface behaviour is significant for its precise performance predictions. The prime aim behind this study is to investigate the behaviour of interface between compacted silty sand soil and concrete counterfaces at (a) different initial void ratios, (b) different surface roughness (smooth and rough) under the influence of different levels of applied vertical stress and test conditions (saturated and constant water content). The second main objective of this study is to investigate the effect of void ratio and the effect of the applied vertical stress level on the variation of matric suction during direct shear tests (matric suction stabilisation, consolidation and shearing stages). To do so, a new loading steel cap of large-scale direct shear apparatus for testing soilsoil and soil-concrete specimens has been manufactured. Firstly, a series of large-scale (300 mm x 300 mm) direct shear tests were carried out on compacted soil samples under different levels of applied vertical stress, void ratios and test conditions (saturated and constant water content). The experimental results confirm the dependency of shear strength, volumetric behaviour and measured matric suction on the vertical stress and initial void ratio. Secondly, to investigate the interface behaviour with different surface roughness (smooth and rough) and compare it with the behaviour of soil-soil samples, a number of interface direct shear tests were conducted between silty sand and a concrete pad under the same levels of vertical stress, void ratios and test conditions. The trend of behaviour of the shear strength versus horizontal displacement curves of soil-concrete interface tests is similar to those of soil tests. The laboratory tests results show that the surface roughness, vertical stress, void ratio and test conditions have significant influence on the shearing characteristics of the interface samples. The study noted that the strain softening behaviour of the tested material is noticeably influenced by the initial void ratio of specimens and surface roughness for both test conditions. From the results, it was observed that the initial matric suction has a clear dependency on the void ratio of the specimens. The shearing behaviour of the soil samples was higher than the rough and smooth interfaces for both studied void ratios and test conditions, whereas, the smooth interface showed lower values of shear strength of all the tested samples. It was noted that there is a remarkable decrease in matric suction during shearing stage with the level of applied vertical stress and the most important matric suction evolution was occurred before the horizontal displacement corresponding to the peak/maximum shear strength achieved.

Finding the location of underground utilities, essentially plastic water pipes, can be difficult and disruptive, which is due to the lack of efficient techniques that can be used to map these buried network services. Vibro-acoustic techniques to determine the location of buried water pipes have been studied within the Institute of Sound and Vibration Research within (ISVR) in the past 10 years. One technique involves excitation of the water pipe where it is accessible, normally from hydrant, followed by measuring the ground surface vibration, at the vicinity of suspecting pipe location. From an earlier feasibility study it was indicated that the emitted ground borne waves from the waves that propagate along the pipe and its contained fluid can help manifest the pipe location. Because the attenuation of the waves is generally large for the plastic water pipe, the pipe ground borne waves cannot be sensed at large distances away from the exciter's location, of order of a few tenths of a metre, or at high frequencies, above 100 Hz. This thesis aims at using an in-pipe excitation source, which can be deployed at any desired location along the pipe length, to overcome the attenuation problem. Although in-pipe sources can transfer energy to the pipe contained fluid and might allow tracking of the pipe at larger ranges, current acoustic exciters are not always appropriate, being cumbersome and too large to fit into a typical buried water pipe. In this thesis, two pneumatic devices were designed with the aim of generating high amplitude signals at low frequencies and with the ability of accessing pipes with a wide range of diameters, down to 1 cm. The devices are experimentally characterised by a series of laboratory tests in a water-filled plastic pipe section. A comparison of the acoustic pressure wave transmitted to a fluid filled pipe between a standard electroacoustic device, an electromagnetic shaker, and the pneumatic ones is made. From the previous work on characterization of wave propagation along plastic water filled pipes, it is known that at below 100 Hz, among all kinds of waves, the axisymmetric fluid borne wave can predominately drive the ground borne wave. Owing to iii the good coupling of the axisymmetric fluid and the shell borne wave they should be considered altogether. The wave speed and attenuation of both waves were measured experimentally, and the results were checked for consistency with the theory. An analytical simulation was developed to explain the reason of high wave attenuation variances obtained from the experimental measurement. Due to the dependency of the axisymmetric fluid and structural borne waves' amplitude to the elastic properties of the pipe a simple experimental method was proposed to distinguish between the pipe wall displacement that arises from the two axisymmetric waves. Such a technique might help assess the condition of pipes through indicating the reduction in their elastic properties due to ageing. From the earlier work on detecting buried water pipes, it was indicated that in addition to the axisymmetric fluid borne wave, the exciter applied to the pipe directly/indirectly drives the ground borne waves with substantial amplitudes. To have a better understanding about the overall response of the ground surface, a simple analytical model was developed, taking into account a ground borne wave emitted from the pipe and the source respectively. Like numerous other digital image processing, in the vibro-acoustic technique, an arctangent operator is used to extract the phase or time delay information, as the assumed ground borne waves are emitted and travel to the measurement point. By virtue of the fact that the arctangent operator produces phase images wrapped between −π to π, an unwrapping operator is required to remove the phase discontinuities embedded within the image. Therefore, a novel phase unwrapping algorithm is developed with a low-cost computational requirement. Furthermore, different state-of-the-art two-dimensional unwrapping algorithms are reviewed and compared for their ability to remove the phase discontinuities, produced by the model. In addition, a drawback of applying one-dimensional unwrapping to the two-dimensional wrapped phase image, used in the previous study, is discussed. To benchmark the effectiveness of the developed pneumatic devices, different exciters such as standard mechanical and electroacoustical exciter are utilised to map a buried pipe. Applying mechanical excitation to the pipe is associated to the earlier feasibility study which repeated for the sake of benchmarking the in-pipe exciters' results against it. Of the exciters, one of the designed pneumatic sources successfully mapped the total length (18 m) of the pipe. Because the aim of this thesis is deploying an in-pipe source to overcome the attenuation problem, the utilised acoustical exciters: the underwater speaker and the designed pneumatic sources are deployed at two more locations along the pipe. The results from each exciter are analysed in detail and compared to each other.

The unacceptable number of casualties and substantial economic losses caused by past earthquakes highlights the high seismic vulnerability of unreinforced masonry structures and the urgent need for resilient and cost-effective retrofitting solutions. In parallel, pressing sustainability requirements foster the need for alternative materials with minimum environmental impact. This study aims at developing an innovative composite retrofitting solution comprising natural fibre textiles embedded in a lime-based mortar (NTRM). Natural fibres have good mechanical properties and excellent environmental credentials, while lime mortars can ensure physical and mechanical compatibility with masonry. Both fibres and mortars are cost-effective and widely available, thus making NTRM systems easily applicable in both developed and developing countries. However, their implementation is hindered by the lack of a comprehensive understanding of their composite behaviour and the very limited experience in structural applications. A systematic and holistic multi-scale experimental programme was undertaken to investigate the performance of NTRM and identify key performance parameters to enable the development of design guidelines. The proposed system was examined at composite level through detailed tensile and bond characterisation, and its effectiveness as in-plane seismic retrofitting solution was assessed through structural tests on medium scale unreinforced masonry walls. The parameters under investigation included: fibre type, textile architecture, mortar overlay thickness, number of NTRM layers, bonded area (length and width), and retrofitting configuration. The results of this study confirm the potential of Flax-TRM as a seismic strengthening solution for unreinforced masonry structures and highlight the importance of yarn and textile architecture on the overall composite performance. Smaller diameter low linear density yarns with a higher level of twist develop a better composite action with the mortar and result in composites with good mechanical properties and high utilisation of the textile tensile strength. The use of mechanical reinforcement ratios greater than 3% were found to spread the cracking well and result in highly ductile behaviour. Flax-TRM was shown to provide significant in-plane strength and ultimate drift enhancement and promote the development of energy dissipation mechanisms, while ensuring structural integrity and delaying the development of brittle failure modes. Based on the experimental evidence and a detailed analysis of shear resisting mechanisms, it is recommended that the shear contribution mechanisms are further investigated, as they were found not to be additive. A simplified design model that accounts for the contribution of the mortar and adopts a more rational effective strain limit that can be developed in the textile is proposed. Finally, design recommendations are provided to inform the selection of suitable reinforcing materials and the design of optimal NTRM strengthening systems.

Sand injectites are observed in a wide range of locations and settings, both modern and ancient but little is known about the processes controlling their formation. The scale of these injections range from mm to km in size and represent the forceful injection of fluidised sand into host strata. Due to the difficulty of observing in-situ events and relative paucity of outcrop data interpretations, understanding of the flow processes during fluidisation pipe formation is lacking. Existing fluidisation models provide mechanisms for fluidisation but remain simplistic and do not capture the full dynamics nor the range of characteristics which are observed to vary both spatially and temporally across the system during the formation of sand injectites. Fluidisation theory relies on an understanding of both the velocity characteristics and the concentration characteristics of a fluidisation event but comprehensive evidence of these quantities has not previously been available. The novel application of experimental techniques in both two dimensions and three dimensions in this thesis provides both high resolution velocity data for the formation and quasi-steady state of fluidisation pipes along with high resolution concentration data for the first time. Complementing this, the novel application of numerical modelling provides insight into the early stages of void formation and demonstrates a new methodology for investigating flow processes during fluidisation. The products of the fluidisation events modelled are presented providing a direct link between fluidisation processes and products for reference in interpreting outcrop data. Residual morphologies are evidenced resulting in explanations of the poor detection rate of sand injections. New models of fluidisation and void formation are presented based on the extensive characterisation of a fluidisation event achieved across multiple methodologies.

This thesis addresses the development of design workflows related to shell structures, covering geometrical, structural and realization aspects. Such workflows are implemented in a parametric environment and they are described in a step-by step process in order to foster their application amongst students and professionals. The scope is to provide practical guidelines in the design of shell structure by means of parametric tools in order to promote its use within architecture practice. The work covers different aspects of the processes, starting from geometrical considerations, form-finding, planarization, structural analysis and optimisation by Genetic Algorithms. The primary scope of the design process is to allow the realization of the structures, developing strategies that can simplify this phase.

Leak/burst events are a serious problem because they disturb customer supplies, lead to water loss and managing them consumes vast resources. Water companies are continually seeking solutions to improve the situation. Presented in this thesis is the development, verification and validation of an integrated framework of methods for determining the optimal configurations of pressure sensors in a DMA and for localising new leak/burst events using a data-driven leak/burst localisation technique. The integration of the leak/burst localisation technique with the sensor placement technique is a novel feature of this framework of methods. A data-driven leak/burst localisation technique, featuring a novel spatially constrained inverse-distance weighted interpolation technique, was developed which quantifies the change in pressure due to a new leak/burst event using pressure sensors deployed in a DMA, without using a hydraulic model. The leak/burst localisation technique combines data from multiple pressure sensors to localise a leak/burst event by interpolating using the distance travelled along pipes. The leak/burst localisation technique was combined with the GALAXY multi-objective evolutionary algorithm to identify the optimal sensor configurations and parameters for the leak/burst localisation technique efficiently. The sensor placement technique automatically determines the leak/burst event sizes for each DMA and groups them to minimise the number of leak/burst event scenarios which are considered. The framework of methods was developed and verified iteratively using data from hydraulic models and a real DMA and validated using data from 20 engineered events conducted in two real DMAs in the UK. During validation, the sensor placement technique identified the optimal sensor configurations from a constrained subset of hydrants in each DMA. The agreement between the leak/burst localisation performance for the real and modelled engineered events demonstrated that the sensor placement technique can accurately predict the expected level of performance which will be achieved in a real DMA, particularly as the number of optimal sensors increases. Engineered events as small as 3.5% of the peak daily flow (6% of the average daily flow) were correctly localised with search areas containing as few as 12% of the pipes in a DMA.

Dome roofs are large structures often subject to variable wind, snow and other loading conditions, in addition to their own weight. A wide variety of structural designs are used in practice, and finding the optimal arrangement of trusses or girders, along with suitable section properties, is a common subject for structural optimization studies. This thesis focuses on self-supported dome roofs for fuel storage tanks, and a variety of optimization techniques are adapted, developed and compared. Various load conditions have been compared using detailed fluid and stress analysis in ANSYS. From results for full and empty storage tanks, with wind and/or snow external loads, the worst cases are for wind loading alone, i.e., snow loading counters the lift force from the wind. Consequently, the case of an empty fuel storage tank subject to wind loading is used as the basis for the structural optimization. To speed up the optimization, a simplified frame analysis was developed in Matlab and integrated with the optimization code. In addition, the wind loads were modelled in ANSYS for a range of dome radii and imported into the Matlab, and a number of different dome designs were used as case studies: these were ribbed, Schwedler, Lamella and geodesic. The principal method used to optimize the frame is Morphing Evolutionary Structural Optimization (MESO), in which an initial overdesigned frame is iteratively analysed and reduced in overall weight by reducing the sections of key frame members. The frame is progressively weakened, but without compromising the structural integrity, until it is no longer possible to reduce the weight. However, there are additional parameters that MESO is not suited to, such as dome radius and those affecting the overall structure of the dome frame (numbers and placements of rings, etc.), and a variety of metaheuristic optimization techniques have been studied: Artificial Bee Colony (ABC), Bees Algorithm (BA), Differential Evolution (DE), Particle Swarm Optimization (PSO) and Simulated Annealing (SA). These can be used instead of MESO, or in a hybrid form where MESO optimizes the frame member sections. Although the focus in this thesis is on minimizing the total structural weight, the importance of other characteristics of the design, especially structural stiffness, is considered and also integrated with the MESO process. The hybrid methods MESO-ABC and MESO-DE performed best overall.

The use of microbially-mediated processes to deal with geo-environmental problemshas raised the interest of geotechnical engineers over the last decade. Of particular interest to this study is the use of bacteria cells to catalyse chemical reactions that can potentially improve the properties of the ground. These bio-mediated methods are based on naturally-occurring processes and provideeffective, sustainable and economic engineering solutions. A frontier of this area of research is the development of the so-calledengineered responsiveliving systems. These systems normally involvethe use of bacteria cells that have been engineered to respond intelligently to inputs from theirenvironment, and they providebenefits that conventional bio-mediated processes are not able to offer. The work presented in this thesis contributes to the development of engineered responsive living systemsfor their use in geotechnical applications. One possible way of developing theseresponsive systems is to use agarose gels as a substitute for soils for the development of early stage physical and computational demonstrators. Agarose gels allow easier monitoring of the performance of the microbes, greater control of the chemical composition of the environment, a controlled simulation over the mechanical properties and a minimised risk of contamination, compared to soils. Thus, the ultimate aim of this research is to characterise at the micro and macro-scale an agarose-based system capable of testing engineered bacteria in a highly controllableenvironment and monitoring their response to external stimulus. The first part of this thesis involves a full-scale characterisation of Agarose Low Melt gel through a series of geotechnical testing techniques, including SEM, triaxial and oedometer testing;the second partfocuses onunderstandingthe growth and distribution of bacteria colonies within a volume of agarose geland exploring the factors that influence their behaviour; and the final partdescribes the development of a computational model that integrates geotechnical simulations with biological data and simulates the effect of a pressure-responsivegel-basedbiocementation system. The successful implementation of such gel-based model will help in the early development of a pressure-responsive bacteria-based systemand will assist in the validation of the proof of concept.

The challenges associated with the construction of large-scale, doubly-curved space-frame structure are significant. This research centres on the development of a novel framework for the reduction of their construction complexity of space-frames by reducing the geometrical variability in their joints and enhancing standardisation. Conway operators are applied to generate an extensive design-space of topologically uniform space-frame configurations, that enables the exploration of materially efficient, and innovative, modular layouts. A novel method for the comparison of the geometry of their joints is then developed, that is invariant under any rotation. This serves as the basis for the evaluation of geometrical variability in a structure and the assessment of its construction complexity, when overlaid with the properties of different fabrication processes. The geometry optimisation of complex, large-scale structures is therefore enabled to reduce the variability in their members and facilitate their construction. The parameters of the computational workflow established can be adjusted, depending on the stage of the project in which the optimisation is carried out, to improve its performance. This workflow therefore suggests an overall shift of the complexity from the construction to the design process, where it can be dealt with by the application of the advanced analysis tools developed. It facilitates the construction of complex structures, promoting an informed application of fabrication processes and thus generating better-engineered solutions.

This study documents the evolution of cementitious and polymeric material development for aerial additive manufacturing (AAM). AAM is designed to bring multi-agent aerial mobility to additive manufacturing (AM, also known as 3D-printing) in the construction industry, in order to create or repair structures in challenging environments, ranging from working at height to post-disaster reconstruction. AAM involves coordinated unmanned aerial vehicles (UAVs - commonly referred to as 'drones') carrying lightweight deposition devices extruding material through a nozzle while in-flight. Prior to this study, investigations into AM construction involved large printing frames or ground-based robotic arms. AM can benefit the construction industry. With the extrusion method, a printed object is built up one defined layer at a time, only depositing material where required thus reducing wastage. Increased automation can reduce labour costs, formwork costs, accidents and fatalities, while offering bespoke design at minimal extra cost. However, the absence of formwork is a major challenge for 3D-printable construction materials while in the fresh state. Suitable rheological properties are needed, as material must possess sufficient workability to pass through a deposition system, yet retain the required buildability, following extrusion, to resist deformation due to subsequent layers. High-density polyurethane foam material was investigated. Cured foam was structurally viable, but fresh properties prior to curing proved rheologically unsuitable for formwork-free extrusion due to excessive lateral deformation. Focus then turned to cementitious materials and the development of novel pastes and mortars suitable for in-situ AAM in a range of environmental temperatures. Mixes are ordinary Portland cement-based and feature a wide range of additives and admixtures. Material was extruded from miniature deposition devices while attached to coordinated flying UAVs following pre-programmed trajectories. Suitable structural material possessed shear-thinning properties promoted by a combination of pseudoplastic hydrocolloids. Fibre volumes were up to 1% for structural compressive material 1700 kg/m3 and 2% for ductile material 1400 kg/m3. Cementitious material developed in this study shows the potential for AAM to be used for rapid, high precision repair work in infrastructure, elevated, marine or tidal applications, in addition to the creation of innovative lightweight structures.

The present work has established a series of grouting performance criteria for low-pH non cementitious colloidal silica grouts, a relatively new fracture filling material which has been suggested for the construction of an underground disposal repository for high-level nuclear waste, known as the Engineered Barrier System (EBS). The research investigation reported here includes experimental analysis of the gelling during the grouting period; a study of the physical and chemical stability of the grout during the post-gelling period; and preliminary first-order modelling of the grout removal process by physical and chemical erosion. Performance comparisons were conducted for three commercially available colloidal silica products; Cembinder, Eka EXP36, and MEYCO MP320, all obtained from Akzonobel Company (Bindzil®). The performance criteria of these three products were subdivided. For the gelling process, the sub-categories of performance studied were the gel induction time, the gel time and the zeta potential. For the physical and chemical stability studies, the sub categories of performance studied were sensitivity analysis with respect to grout age, channel length and salt release, and groundwater salinity, cation content and flowrate. For a low saline groundwater condition, an overall comparison of these sub-categories was expressed in property Radar charts. It was found that the gelling time increased in the order of Eka EXP36 < Cembinder < MEYCO, similar trend was found in grout removal resistance for both initial erosion and4 Public chemical dissolution at high salinity groundwater condition. This observation suggests that the grout size distribution is the major contributing factor in the overall grout removal analysis, grout with larger particle size tends to have stronger grout removal resistance in high saline groundwater intrusion. This comparison provides a simple guidance for future grout selection. An alternative method was introduced for gel induction time measurement during the gelling process. It was defined as the point of intersection between loss and storage moduli. Furthermore, a grout mixing recipe was introduced for each of the three grouting products, in order to maintain a target operational time between 10-33 minutes. Grout stability post-gelling was studied. The physical stability (resistance towards physical erosion) was measured by the turbidity of outflow solutions, whereas the chemical stability was measured by dissolved ion concentration due to silica dissolution at the outflow. The preliminary first-order life span estimation of the grout barrier in the Engineered Barrier System was found to be relatively short.

Arising in the far-field of large explosions, long duration blast events are typically defined as having a positive phase duration in excess of 40ms. Capable of engulfing entire buildings, long duration blast waves can result in significant damage to a multitude of compression elements, potentially leading to total structural collapse. Current guidelines provide simple empirical methods for estimating peak response and damage state of a column to blast loading. These methods neglect more complex situations such as non-orthogonal structural orientation, combined blast and thermal loading or column position within a frame: all requiring extensive experimentation or numerical modelling to determine a damage state. In this thesis, multi-axis, thermal and frame interaction effects on the structural response of a column to long duration blast were explored. One phase of experimental testing improved the understanding of explosive thermal energy application to I-section surfaces. Another phase of testing explored the response of partially-clad frames to long duration blast utilising experimental findings, an extensive numerical study was undertaken, exploring the response of a column to large scale blast events including combinations of all three effects. Results were quantified and consolidated into a series of end-user charts, akin to those found in the current design standards. These charts provide a quick and simple means of estimating the maximum displacement and corresponding damage state of a column to long duration blast with multi-axis, thermal and frame interaction effects: reducing future requirement for experimental testing and numerical modelling. Findings indicated that a combination of all effects can have a detrimental impact on response, in some cases increasing damage state from minor to total destruction and collapse for the same column to the same blast event.

Previous records of fire and blast incidents have shown the extensive damage that these actions can cause in building structures in general and steel buildings in particular. Therefore, it is crucial that strategic facilities are designed to withstand these extreme loads with as little damage as possible. However, the design of structures to resist blast and fire actions has typically been carried out prescriptively and without consideration for the uneven distribution of temperatures in large building compartments typical of today's architectural practice. Blast pressures due to explosions are also likely to be followed by travelling fires in these compartments. Moreover, due to the significant level of uncertainty involved, a performance-based framework is likely to be more suited for the design and assessment of structures subjected to these loads. This thesis aims to investigate the structural performance of steel structures under travelling fires as well as multi-hazard conditions involving blast and travelling fires from a performance-based perspective. Non-linear finite element analyses are carried out on steel frames considering various travelling fires and post-blast travelling fire scenarios. The PEER performance-based framework, originally developed for seismic actions, is tailored and used to assess the building performance under these actions. The results show that the structural response could be underestimated or overestimated by up to 30 % when there is significant correlation between the maximum compartment temperature and the length of travelling fire for very low probabilities of exceedance. Under post-blast travelling fires, the first storey is likely to be the most critical storey, and blast and fire parameters can significantly affect the structural response. Moreover, correlation effects between maximum compartment temperature and blast overpressure are found to be more significant when low exceedance rates are considered. The results of this research demonstrate that a performance-based assessment can be used to examine the response of steel structures under these extreme loads and to assess the efficiency of different structural systems. It can also potentially lead to great savings in the cost of blast and fire protection required.

The disposal of scrap tyres has become a major environmental problem around the world. For its recovery, a geomaterial has been used as part of civil constructions, commonly known as Rubber-Soil mixture (RSm). The use of RSm has the potential to be used as geotechnical seismic isolation system and hence provide protection against earthquakes. However, the static and dynamic behaviour of RSm is not well understood. Various bulk (macro), particle (micro) properties, and the test conditions affect its characterisation. Whilst addressing this knowledge gap, the aim of this study was to understand the response of RSm under cyclic loading and evaluate its effectiveness in attenuating accelerations when used to retrofit a soil foundation. An experimental programme was chosen for this research and is divided into three scales; particle, element and 1g model scales. Plain strain visualisations, oedometer, and x-ray tomographic tests were performed to elucidate RSm particulate behaviour. To understand RSm dynamic behaviour, the evolution in stiffness and damping of the mixture was analysed from small-to-large deformations whilst altering rubber content and number of cycles. A sweep analysis was also performed via 1g shaking table tests to evaluate the cyclic performance of a scaled foundation-modified soil with RSm. The findings in this thesis revealed that the macro behaviour of RSm is highly influenced by the particle properties, including rubber mass, size, shape, stiffness and its interaction with sand particles. Tests showed a greater change in void ratio of mixtures containing shredded rubber compared to crumb rubber. 3D x-ray tomographic images revealed an increase in contact and a decrease in rubber volume of RSm under loading. This demonstrated that the high RSm compressibility is the result of both particle re-arrangement and rubber distortion. At an element scale, liquefaction resistance increased and mixtures did not liquefy by adding 20% rubber. The addition of rubber led to a reduction in soil stiffness whilst it increased the mixture resilience against cyclic loading, ameliorating the cyclic effect on stiffness and damping degradation. Material damping increased with rubber content at small-to-medium strains, whereas an upper value was revealed by adding 10% rubber at larger deformations. Test results supported the basis that energy dissipation in RSm is generated through particle sliding and rubber deformation, which takes over the dissipation mode after several cycles. Altering a host soil system by adding vertical discrete zones with RSm showed a lower amplification ratio and as a result mitigated part of the incident vibrations. The increase in damping capacity at a model scale was postulated to be the result of combining geometrical and material damping. The vertical disposition of the soft zone herein proposed could allow its application to both existing and new infrastructure.

System identification is an important technique in reconstructing and estimating dynamic states, unknown parameters and unmeasured inputs of dynamical systems using measured input-output signals, and in minimizing the gaps between real engineering systems and their mathematical models. Whether a system for a given setup of sensors can be, in theory, successfully identified is associated with its observability properties. This thesis is overall devoted to two research directions: 1) developing efficient observability algorithms for handling large and complex dynamical systems and 2) incorporating unmeasured or unknown inputs into robust observability computation and tool. The research is motivated by the need to relax the computational limitation of the existing observability methods that is associated with their high physical memory requirements when used for large and complex real systems, as for example large civil infrastructures encountered in Structural Health Monitoring (SHM). Moreover robust observability computation with the consideration of unmeasured inputs is needed to account for joint state-parameter-input identification problems which have gained increasing attention in recent years. In particular, two efficient and robust algorithms are proposed to test observability properties in Chapter 2 and Chapter 3. The first algorithm applies to large linear systems with unknown parameters, based on the efficient implementation of the Observability Rank Condition (ORC) method. The second algorithm applies to rational nonlinear systems with unmeasured inputs, based on the extended use of the extended Observability Rank Condition (EORC-DF) and a power series-based computational framework. In Chapter 4, computational frameworks are developed for Lie symmetries of nonlinear systems with unmeasured inputs. The obtained Lie symmetries can provide an alternative path to approach the observability properties of a system for a given setup of sensors. More importantly, Lie symmetries imply the mathematical relationship between the true solutions of the system's states, parameters and unmeasured inputs and their other possible solutions. Finally in Chapter 5, the application of observability and Lie symmetry analyses is illustrated through a complex, nonlinear and non-smooth mechanical model. The model is successfully reduced and identified using suitably chosen identification methods.

Liquefaction-induced damage, in the aftermath of an earthquake, is a major source of failure for foundations and earthworks. Understanding soil behaviour and its response both for pre- and post-liquefaction scenarios is an area of active research. The main aim of the research presented in this thesis is to describe the post-liquefaction behaviour of sand using a state-dependent approach instead of the conventional approach based on relative density as the governing parameter. To fulfil this aim, the author has carried out soil element tests, conducted and gathered information from real field case studies, and has modelled soil using a numerical modelling approach. The soil element tests consist of a series of monotonic and multi-stage triaxial tests carried out on Redhill 110 sand (this particular sand was chosen because of its high susceptibility to liquefaction and used in previous liquefaction studies) to investigate its post-cyclic behaviour. The results are utilised to propose a state-dependent procedure to evaluate the post-liquefaction behaviour of the sand. These findings are subsequently used to develop a set of instability curves for the assessment of post-cyclic deformation of liquefied sloping grounds. These curves define the level of strain that the liquefied soil has to mobilise before regaining strength and stiffness and developing the characteristic strain-hardening behaviour observed in the element tests. Another series of triaxial tests is conducted on Kumamoto sand. The aim of these tests is to investigate the post-liquefaction response of a naturally deposited soil. The results are utilised to describe the post-liquefaction behaviour for the soil using a state-dependent approach. To validate the proposed instability curves, a case study which focuses on the failure of the Lower San Fernando Dam observed after the 1971 earthquake is conducted. The results show that the proposed post-liquefaction instability curves can be used for the preliminary stability assessment of sloping grounds in liquefiable soils in which a static shear stress component is present after the end of the ground shaking. The author also conducted another case study based on a field investigation carried out in the area affected by liquefaction phenomenon after the 2016 Kumamoto Earthquake sequence. The main finding from this investigation is the limited structural failure in the Kumamoto Port area despite clear liquefaction manifestations. The strain-hardening behaviour for liquefied soil observed in the element tests provides a reasonable explanation for the unexpected finding from the field survey. A numerical model is also built to study the site response analysis for Kumamoto Port to provide further insight into the limited effects caused by liquefaction. Finally, to investigate the capability of existing constitutive models to capture the post-cyclic deformation of the sloping ground and compare the results with the proposed instability curves, the thesis presents the results of a two-dimensional slope modelled using the Manzari-Dafalias constitutive model. The results show that the numerical model is capable of predicting the post-liquefaction deformation of sloping ground if considering the aftershocks in the analysis.

Despite the unprecedented permeation of Building Information Modelling (BIM) and availability of a wide range of collaboration platforms, architects and structural engineers, for the most part, act as separate teams. Therefore, linking architectural models with those of structural engineers remains a labour-dependent and a cumbersome activity. This research proposed potential solutions to improve the structural design processes at the early stages by integrating architectural and structural models and generating alternative structural models for the same architectural model automatically. The research proposed a framework and a proof-of-concept prototype, which used the architectural model and relevant parametric data as input to design and analyse different parametric structural models through an automatic process. This process helps to reduce the iterative structural design process and improve the collaboration between the structural engineers and architects through automation within the BIM platform. The research leveraged the importance of using automation in the structural design process and the collaboration between structural engineers and other disciplines, particularly with the architects. The research started with an exploratory approach, using a comprehensive literature review to highlight the existing challenges in the structural design, analysis and optimisation processes, particularly at the early stages. Thereafter, based on the information received from the literature review a Conceptual Structural Design and Optimisation (CSDO) framework was developed to solve the identified challenges. In order to justify the research and validate the conceptual framework, an online questionnaire was distributed between professionally accredited structural engineers of the Institution of Structural Engineers (IStructE), The Institution of Civil Engineers (ICE) and the American Society of Civil Engineers(ASCE). The questionnaire uncovered valuable information about the existing challenges, and potential solutions that justifies the research knowledge gap, and the information obtained helped to improve the framework. Thereafter, an extended framework was developed and aimed at improving the integration and interoperability between architectural and structural model in an automatic process in BIM. Hence, a proof of concept prototype was developed to demonstrate the workability of the extended framework. Various case studies demonstrated the workability of the prototype in different areas and type of structures. Finally, the proof of concept prototype was validated in several semi-structured interviews with the academic staff of the University of Portsmouth and chartered structural engineers in industry with civil and structural engineering backgrounds. Furthermore, a focus group was conducted with six domain experts from the Autodesk research and a development team to validate the prototype and receive feedback for further development and future work. This research contributes to the field by presenting a novel solution, capable of automated generation of structural design, based on architectural models and design requirements (input data). This research provides a practical demonstration of a fully integrated architectural/structural design system. Moreover, this research contributes to the field by extending the outcomes of existing literature that proposed optimisation of structural design, albeit in one dimension, like shape, topology and size in structural design. The proposed framework and proof of concept prototype considers all the dimensions of the optimisation simultaneously and provides a valuable source of reference for future research in this area.

Structures loaded cyclically beyond their elastic limit experience gradual accumulation of plastic deformations or strains which may eventually lead to material deterioration and ductile fracture. Assessing the life expectancy of their structural members requires the development and implementation of appropriate material models into the finite element environment, using robust numerical integration schemes. It is the purpose of the present Thesis to investigate through rigorous numerical analyses and experimental testing the mechanical behaviour of metal components subjected to intense cyclic loading. Advanced numerical tools are developed to simulate multi-axial material ratcheting and cyclic plasticity-damage response in metal structural components. The ultra low-cycle fatigue of high-strength steel welded tubular joints is also investigated through large-scale experiments. An implicit numerical scheme is proposed in Chapter 2 for simulating the mechanical response of thin-walled structures subjected to inelastic cyclic loading. The constitutive model is formulated explicitly for plane stress conditions, accounts for combined kinematic/isotropic hardening and follows the von-Mises yield criterion. Emphasis is given to kinematic hardening part, which is described with an advanced multiple backstress model suitable for multi-axial material ratcheting simulation. Constitutive relations are integrated implicitly using the Euler-backward integration technique. Two main novelties of the algorithm refer to the incremental update of the internal variables through the solution of a single scalar equation, and the explicit formulation of the consistent tangent moduli. The numerical scheme is implemented into the finite element software ABAQUS (2016) as a material user-subroutine UMAT and its capabilities are demonstrated through the numerical simulation of large-scale experiments on pipe elbows, a characteristic mechanical component that experiences multi-axial ratcheting response. In the sequence, the proposed numerical scheme is employed to investigate the ratcheting collapse of dented externally pressurised tubular circular members subjected to cyclic axial loading. The numerical implementation of coupled cyclic plasticity-damage models is presented in Chapter 3, suitable for simulating low-cycle fatigue in metal components. Constitutive relations account for J2-flow theory with nonlinear kinematic/isotropic hardening, coupled with isotropic continuum damage mechanics. The damage potential is written in a general form, allowing for implementing any isotropic damage model reported in the literature. The constitutive relations are integrated implicitly considering in the most general case the 3D finite element formulation. An additional numerical scheme is proposed explicitly for plane stress conditions by extending the plane-stress projection method to the requirements of the model. Both numerical schemes feature computational efficiency as incremental update of internal variables is achieved through the solution of a single scalar equation. The integration algorithms are consistently linearised to ensure numerical robustness in large-scale computations. The proposed numerical schemes are implemented into ABAQUS (2016) software as user material subroutines UMAT and are validated against large-scale tests on pipe elbows that failed from ultra low-cycle fatigue. In the last part of the Thesis, the ultra low-cycle fatigue performance of welded tubular X-joints is examined, motivated by the need of safeguarding the integrity of offshore platforms under extreme loading conditions. Seven specimens, representing X-brace joints of a bottom-founded offshore tubular jacket with a scaling factor of 1:3 are tested under strong, fully-reversed cyclic in-plane bending. The seven specimens formed a through-thickness fatigue crack within less than 100 cycles, simulating extreme loading conditions. Rigorous finite element models are also developed, with emphasis on constitutive modelling, to simulate the cyclic loading procedure, providing very good comparisons in terms of load-displacement response and local strain predictions during the initial loading cycles. The experimental data are compared with a large dataset of low-cycle fatigue experiments on welded components, reported in the literature for mild and high-strength steel materials, as well as with existing design provisions.

The conventional design of retaining walls is typically based on ultimate limit state calculations with arbitrary factors of safety, while the assessment of wall deformations is based on serviceability limit state calculations. Such an inconsistency has caused much uncertainty and hence inevitably excessive conservatism in retaining wall designs. The aim of this research is consequently to propose a design method for retaining walls in sand, considering safety and serviceability simultaneously, based on the exploration of sand deformation mechanisms and earth pressure behaviours mobilised with retaining wall movements. The first group of six centrifuge tests was conducted to investigate loose and dense Hostun sand behaviours with a complete set of rigid wall movement modes, i.e. rotation about the base, translation and rotation about the top. Sand deformations and earth pressures were measured and analysed by Particle Image Velocimetry and a Tekscan pressure mapping system, respectively. Simplified deformation mechanisms compatible with active wall movements and a simplified calculation method for the peak maximum shear strain caused by passive wall movements have been proposed based on the analysis of measured sand deformations. Observed earth pressures were quantitatively linked to sand shear strains in order to build simplified constitutive laws approximately characterising the earth pressure mobilisation with active and passive wall movements. A novel design method has subsequently been successfully proposed for flexible retaining walls in sand based on the simplified deformation mechanisms and constitutive laws, validated by the second group of three centrifuge tests involving a flexible retaining wall and two field measurements for the excavations supported by cantilever and propped retaining walls. Such an adaption from rigid wall results to flexible wall designs has completely applied the mobilisable strength design method to geotechnical projects in sand. This novel design method, for the first time, allows designers to rapidly assess the performance of different wall geometries and construction sequences in sand, providing extremely valuable contributions to practical engineering.

Fractures are considered to be both problems and opportunities for exploration and production from petroleum reservoirs. The main aim of fracturing an oil medium is the stimulation of oil and gas production by inducing highly conductive channels leading to a well, from which hydrocarbons will flow. Many applications of hydraulic fracturing take place in soft sandstones using moderate to low viscosity fluids. Soft sandstones represent the host rock for a large portion of active aquifers and oil and gas reservoirs because their high porosity both enhances storage and facilitates extraction. The transitional nature of sandstones, in particular, presents some challenges to the safety of these operations and the understanding of the mechanical response of these materials under a variety of conditions is poor. The motivation of this research was to gain understanding of the fracture mechanics of soft media under low viscosity fluid injection. Synthetic rock specimens were generated via microbially induced carbonate precipitation (MICP), providing virtually limitless quantities and had customisable characteristics, allowing relevant structural parameters to be varied independently, and hence isolating their effects. The method was applied to produce realistic weak sandstone-like materials from a base sand through a bio-process that builds up calcium carbonate cementation around the particles. Once a single recipe was developed and the uniformity of the specimens and repeatability of process were assured, the mechanical and physical properties of the specimens were assessed with varying base materials (grain size, shape, width of particle size distribution) and levels of cementation. The artificial rocks sufficiently resembled soft sandstones to be used as a substitute in the subsequent laboratory investigation of the hydraulic fracturing experiments. Fracturing experiments were conducted with both cohesionless sands and bio-cemented samples at various confining conditions, flow rates, fluid viscosities, cementation levels and various base materials. The main aim was to get an insight into how each individual factor affects the fracture patterns and pressure response. For those experiments, two experimental setups were developed explicitly for this project that were able to apply actively or passively stresses to the medium which was repre- sented in three dimensions. The transitional behaviour of weakly cemented sandstones was clearly seen on both the fracture patterns and pressure responses obtained when conducting the hydraulic fracturing tests. The fractures transitioned from plane-like to string-like as the cementation level increased, while the deviation between the breakdown and propagation pressures was also more pronounced. Many observations in the literature concerning the fluid properties and rates were confirmed in this work, but also new information was added because of the ability to visualise the fracture initiation and propagation. The work conducted in this research bridges previous works on two-dimensional media, where visualisation of the fracture was possible, and three-dimensional media, where only post-test observations could be made.

The contamination of soil and groundwater is a widespread issue that can adversely affect human health and ecosystems. The containment approach using cut-off walls is one of the most commonly-used land remediation technologies. However, the cut-off wall materials inevitably deteriorate under mechanical, chemical, and environmental stresses. The damage of cut-off walls can undermine their mechanical and transport properties, impacting their serviceability and reliability. This PhD research develops crack-resistant and self-healing cut-off wall materials incorporating polymers and minerals. The overall performance of four additives, including superabsorbent polymers (SAPs), oil sorbent polymers, reactive magnesia (MgO) pellets, and microencapsulated sodium silicate in two cut-off wall materials (cement-bentonite slurry and cement mixed soil) is the interest of this study. In general, the addition of the SAPs and oil sorbents has negligible or only slightly adverse effects on the rheology, cement hydration, strength, and permeability of the cut-off wall materials. The crack resistance of cement-bentonite mixes is greatly improved by SAPs under wet-dry cycles, and the soil mix samples demonstrate enhanced self-healing performance thanks to the swelling of the SAPs. Similarly, the swelling of the oil sorbents managed to block 500µm-wide cracks completely, and the oil sorbent-containing samples show a marked recovery of permeability. The expansive hydration and carbonation of the MgO mineral also achieved effective healing by producing depositions and crystals on the crack surfaces of the cut-off wall materials. Microencapsulated sodium silicate, as another mineral healing agent, is released into cracks when the microcapsules rupture, and reacts with the cementitious matrix to fill and heal the cracks. The results demonstrate the improved average crack mouth healing and recovery of permeability provided by the microcapsules. X-ray microcomputed tomography and scanning electron microscopy were innovatively applied to investigate the self-healing process and mechanism. The microstructural analyses confirm the survivability, uniform dispersion, and crack-triggered rupture of the microcapsules, as well as the release of the healing agent and the generation of healing products within the cracks. These results collectively demonstrate the great potential of these four polymer and mineral additives as crack-resistant and self-healing agents for cementitious cut-off wall materials, which could provide more resilient, sustainable, and reliable cut-off walls with significantly enhanced durability, reduced maintenance costs, enhanced safety, and protection against sudden or undetected failure.

Damage in buildings documented after recent earthquake-induced liquefaction events emphasises the importance of improving vulnerable regions using countermeasure techniques. Further investigations are required to evaluate the performance of currently available mitigation techniques. Vertical drains are an effective countermeasure technique, extensively utilised to reduce damage, as rapid dissipation of excess pore pressures can be achieved in case of liquefaction. However, further research using physical and numerical modelling techniques, centred on the behaviour of drain arrangements below structures is required in order to generate knowledge concerning the issue of their performance in the presence of buildings. Dynamic centrifuge modelling has been employed in this work to improve understanding related to the performance of drain arrangements in earthquake-induced liquefaction below new and existing structures. The analysis considers the use of recycled material as an alternative to coarse gravel inside the drains and proposes a simplified technique for the accurate simulation of the drain behaviour during soil reconsolidation. The influence of the foundation bearing pressure as an important factor in the performance of the drain arrangements was observed during and after the shaking, in the evaluation of a simplified arrangement of vertical drains under new buildings. Excess pore pressures were controlled and rapidly dissipated due to the significant confining pressure exerted by the foundation, enabling lower foundation settlement and great rotational response in the case of a heavy foundation. The "unit cell" and "infinite cell" behaviour of the internal and perimeter drains was accentuated in the presence of the structure. The performances of different alternatives of rubble brick vertical drain arrangements were evaluated, with a focus on providing an optimal treatment to the vulnerable area below the foundation. Improved control and dissipation of excess pore pressures, including enhanced foundation settlement response were achieved when adding edge drains below the foundation in a 13- vertical drain arrangement, due to the higher area replacement ratio in the soil. Moreover, the lower soil softening generated in the stratum with 17- vertical drain arrangement, enabled a great rotational response of the foundation. Countereffects in the effective performance of the arrangement of 17 drains were also presented during the reconsolidation stage, as a delay in the flow front arrivals of the external drain rings was registered. The foundation settlement improvement was lower than expected when adding the edge drains below the foundation, due to the bulging effect presented at the top of the drains. The alternative of replacing internal and edge drains utilizing aluminium encased vertical drains below the foundation showed an improved behaviour of the soil principally during dissipation compared to the original arrangement. Improved settlement response was obtained using this variation, together with a consequent greater seismic demand of the foundation due to the effective performance of the edge and internal drains and the greater shear reinforcement provided by the columns. In addition, a comparative analysis in which the 17- vertical drain arrangement and the single rubble brick column that covers the entire foundation footprint were evaluated, highlighted the importance of considering external drain rings in the arrangement, capable of reducing the "infinite cell" behaviour of a single drain during the shaking. The foundation settlement response obtained in all the tests, highlights the relevance of an optimal performance of the arrangement during the shaking, rather than only the soil reconsolidation stage. Inclined rubble brick drain arrangement around existing buildings was evaluated as a feasible and economical alternative mitigation technique. Excess pore pressures were controlled and easily dissipated below the foundation due to the inclined columns radial proximity in the direction of the structure along the stratum depth. In addition, an improved settlement response of the foundation was obtained compared to that over an arrangement of vertical perimeter drains. A larger rotational response was also attained for the foundation in the case of inclined drains, in response to the relatively lower soil softening. Furthermore, the high-bearing pressure of the foundation significantly influenced the effective performance of the inclined drain arrangement, enabling a lower settlement response compared to a lighter foundation. A simplified 3D finite element technique was developed using ABAQUS software to simulate principally the dissipation behaviour of a soil considering a drain arrangement below new and existing buildings. This simplified method allows to obtain the adequate permeability of the drain coarse material for an optimal response of the foundation in terms of settlement, becoming a valuable tool for practitioners. The models evaluated using centrifuge methodology were also analysed utilising this technique, thus, the validation of the proposed method was possible. The model calibration was performed by varying the soil stiffness and permeability parameters in order to obtain a correct simulation of the soil during and after the shaking. Accurate simulation of excess pore pressure generation was achieved, particularly for traditional vertical arrangements, in small soil stratums. The constant soil stiffness and permeability during the reconsolidation stage, represent the principal limitation in the correct simulation of the soil behaviour, as a slower rate of soil reconsolidation was obtained after the shaking in the numerical model compared to the physical model. The proposed technique was considered satisfactory as a similar settlement response of the foundation was obtained in both the numerical and physical analyses.

This thesis is concerned with the mechanical aspects of fluid-vegetation interaction in coastal flows and their resultant instabilities. Specifically, we consider the evolution of periodic waves as they propagate through vegetated domains, and the emergence of monami - the progressive, synchronous oscillation of submerged vegetation under sufficiently strong flows. We divide our analysis between rigid and flexible vegetative canopies. These new predictions and physical insights will be applicable in the analysis of a diverse range of industrial and environmental applications involving fluid-vegetation interactions. In the case of rigid vegetation, using the method of multiple scales, we derive the evolution of small-amplitude waves propagating over a varying substrate fully covered with vegetation. In particular, we give time-averaged predictions for both the amplitude and the wavelength of the waves as functions of the distance of propagation. We then extend this analysis to include the situations of (i) combined current-wave flows and (ii) shallow-water waves through vegetation. For the case of combined current-wave flows, we demonstrate the manner in which the surface waves vary as a function of the current, and also how the current remains unaffected by the evolving wave. For shallow-water waves, we explore how cnoidal waves, nonlinear periodic solutions of the Korteweg-de Vries equation, evolve on horizontal substrates. For all of the flows considered above on rigid vegetation, their evolutions are only drag-dependent and hence independent of added mass and virtual buoyancy. In the case of flexible vegetation, we propose a model where the plants are described by elastic cantilever beams. Our first analysis concerns the propagation of small-amplitude waves. Compared to the case of rigid vegetation, the fluid will load and deform each vegetative structure. This deformation, in turn, must affect the flow. Although the flow and the beam dynamics have to be determined simultaneously, we show that when the wavelength is sufficiently small, such quantities are asymptotically decoupled -- this allows us to first determine the local beam dynamics before evaluating the momentum loss in the macroscopic flow. In contrast to rigid vegetation, we find that added mass and virtual buoyancy play a role. Finally, we focus on understanding the mechanisms and critical conditions for triggering monami. We treat the current as unidirectional and solve for the steady configurations of the flow and the deflected canopy. Our stability analysis predicts that monami is induced by shear along the top of the canopy. Meanwhile, monami can be suppressed if the canopy is sufficiently sparse or if there is sufficient inertia in the system.

Understanding the hydration and microstructural evolution of cement has been a controversial subject for many decades. As a result of this, different techniques have been used to assess cement hydration. One of the techniques which has demonstrated to be a sensitive and useful technique is Alternating Current Impedance Spectroscopy (ACIS). However, this technique is not yet fully accepted by the cement research community and industry. This has been particularly evident in many cement studies at early hydration ages (>24hrs) in which the ACIS information available at this time is very limited due to instrument and data interpretation limitations, and the complex chemical composition, and continuous pore solution and microstructural development of cement paste. In this project, a custom-cell design is proposed to perform ACIS measurements in cement paste at early ages (>24hrs). The selection of the custom-cell is systematically assessed through a rigorous selection process of the cell components and experimental protocol. To evaluate the performance of the custom-cell design and demonstrate the capabilities of ACIS as a probe of cement hydration and microstructural development at early ages, three techniques (i.e. isothermal calorimetry, Vicat needle test, and scanning electron microscopy) are used as a benchmark to support and complement ACIS data interpretation. The results show that ACIS measurement can be performed at early cement hydration ages by using the proposed custom-cell design (decreases parasitic effects at high frequencies). The benchmark techniques demonstrated that ACIS is a promising and capable characterisation technique to assess the characteristics of the pore solution, thermochemical and microstructural changes during cement hydration. However, further experimental work is required to take further the potential of ACIS.

The mechanical behaviour of sands at low confining stresses may have important implications for the design of offshore wind turbine (OWT) foundations. However, previous research investigating this behaviour is limited and conflicting, and cyclic testing campaigns have historically adopted load characteristics that may be unrepresentative of those sustained by OWT foundations. This thesis endeavours to fill the gap in the literature through creation of a new experimental database of soil element tests, that explores the constitutive response of sand at low stress levels subjected to monotonic and cyclic loading. Results of the monotonic experimental campaign indicate that while the shear strength properties (ηmax and ϕ'max) tend to increase with decreasing effective confining stress, σ'c,0), this effect becomes increasingly minor for σ'c,0≤ 50 kN/m2. Furthermore, tests undertaken at lower confining stresses exhibit a comparatively stiffer response than those tests sheared at higher pressures. Results of the cyclic triaxial testing campaign exemplify the complexities of the response of sands subjected to cyclic loading. However, clear and systematic trends are found that can be robustly captured by the new cyclic modelling framework adopted in this study. Modern design methods for OWT foundations increasingly rely on finite element analysis (FEA); however, results depend critically on the constitutive models used, and the model parameters adopted in the numerical analyses. This thesis reviews the state-of-the-art with regard to constitutive modelling frameworks developed for predicting sand behaviour. Evaluation of four sophisticated constitutive models found that it was not possible to determine a single set of calibrated model parameters that yield satisfactory model simulations for both drained and undrained load cases. Furthermore, only the general trends could be predicted when simulating sustained undrained cyclic loading. Further model development is therefore required if such models are to be relied upon for predicting the long-term behaviour of OWT foundations.