Browsing by Author "Priest, Jeffrey Alan"

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    Effects of FRP Cross-wall Connectors in Multi-wythe Masonry Walls
    (2016-01-13) Elrayes, Mahmoud; Shrive, Nigel Graham; Valluzzi, Maria Rosa; Nowicki, Edwin Peter; Wong, Ron Chik-Kwong; Lissel, Shelley Lynn; Shrive, Nigel Graham; Priest, Jeffrey Alan
    The seismic performance of multi-wythe masonry walls is known to be generally poor, as they can exhibit local failure modes by wythe separation and collapse of the external wythes. For retrofitting them, it is widely acceptable to install transverse ties in combination with other intervention methods to provide proper connections between the wythes. The value of using transverse ties in heritage multi-wythe masonry walls has been questioned in recent research. Different finite element models were developed to simulate the behaviour of traditional transverse ties installed in multi-wythe walls. A simplified micro-model provided insight regarding stress transfer between the different elements of the system, and suggested that the traditional distribution of ties is inefficient. Macro-models were used to investigate the role of a single tie in resisting different loading conditions and found that the effect is minimal in most cases. The findings were in agreement with previous experimental research. An experimental program was performed to investigate non-traditional configurations and distributions of transverse ties. Large scale three-wythe walls were constructed and subjected to axial compression and lateral in-plane cyclic loads. Transverse ties made of FRP rebar were installed at different angles to the wall surface as opposed to the traditional leveled and perpendicular to the wall surface approach. Differences in the behaviour of the ties were observed including connection technique to the wall as well as the ability to transfer shear loads if placed in certain locations. Inclined transverse ties were grouped to form semi-continuous vertical, horizontal and diagonal elements to produce certain improvements in the structural performance of the wall in terms of lateral strength, stiffness degradation, energy dissipation, and post-peak behaviour.
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    Experimental Studies on the Geomechanical Behavior and Heterogeneity in Laboratory Synthesized Hydrate-bearing Sands
    (2023-09-21) Pandey, Mandeep Raj; Priest, Jeffrey Alan; Hayley, Jocelyn L.; Wan, Richard G; Wong, Ron Chik-Kwong; Bryant, Steven L.; Pinkert, Shmulik
    Hydrate-bearing sands (HBS) store large volumes of methane gas, and along with their potential to be commercially exploited using current oil and gas production techniques, make them suitable as a future energy resource. When hydrates form in the pore space of a sediment, they significantly increase the strength and stiffness of the host sediment. The enhancement in mechanical properties is influenced by various factors, such as hydrate saturation, in-situ stress conditions, sediment type (fine-grained or coarse grained). Our current understanding of HBS behavior is based on studies of laboratory synthesized hydrate-bearing specimens, however significant variation in reported values exist that has been suggested to arise from differences in hydrate formation methods, test apparatus, test conditions. Results from testing natural HBS samples, obtained from offshore India, suggest that the particle size impacts geomechanical properties. However, laboratory studies on synthesized specimens are typically conducted on sand specimens with narrow particle size distributions (PSD) and exclude larger particles. As such, there is a lack of understanding of what may lead to variations in mechanical properties of HBS. This thesis reports on a comprehensive experimental program conducted on laboratory synthesized hydrate-bearing sands for two different PSDs, whose particle size was chosen to better represent the coarse fraction observed in natural cores. The laboratory study included detailed analyses of the shear modulus evolution during the formation of hydrates in the pore space of sands. The research also explored the effect that the initial water saturation had on the pressure and temperature conditions when hydrate formation was initiated, along with how it impacted the stress-strain response after hydrate formation. The results from the extensive testing highlighted an inherent heterogeneity in geomechanical behavior of HBS specimens formed and subjected to similar conditions. Conceptual models were developed to help visualize the experimental observations and gain better insights into the factors that led to differences in formation characteristics and resulting hydrate morphology that developed within different sands. The results of this study highlight that the variations in the geomechanical behavior of HBS reported in literature may arise due to the heterogenous distribution of hydrate within laboratory synthesized HBS studies, which is also likely to exist in natural hydrate bearing cores. Observations from the testing will help researchers better understand the behavior of HBS over a wide range of sediment types and formation conditions, like under permafrost, or within offshore seabed sediments.
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    Hydro-Mechanical Coupling and Failure Behavior of Argillaceous Sedimentary Rocks: A Multi-Scale Approach
    (2019-04-26) Eghbalian, Mahdad; Wan, Richard G.; Wong, Ron Chik-Kwong; Epstein, Marcelo; Priest, Jeffrey Alan; Regueiro, Richard A.; Shrive, Nigel Graham
    This thesis aims at characterizing the hydro-mechanical behavior of argillaceous sedimentary rocks within a novel poro-elasto-plasticity framework that encompasses micro-mechanics and a multi-scale approach. The developed model considers argillaceous sedimentary rocks to be comprised of a mixture of clay aggregates and rock-type inclusions. The clay fraction has a dual porosity arising from micropores at the clay aggregate level and nanopores between the clay platelets that form the clay aggregates. The rock-type inclusions also have a dual porosity due to the presence of microcracks embedded into a nano-porous rock matrix. As such, the work develops multi-scale modeling techniques that elucidate the complex macroscopic characteristics observed in clay-rich rocks by advocating only the primitive physical laws at their fundamental scales. The outcome is an analytical constitutive law that transcends the various scales: from nano- to macro-scale. Therefore, the swelling stress originating in the nano-pores of clay particles and capillary stresses in the porous network, as well as micro-crack growth can be readily computed as a function of microstructure and physics across the various scales. The developed model is implemented within numerical modeling frameworks such as Finite Element Method (FEM) and eXtended FEM. Lab experimentally observed phenomena in argillaceous sedimentary rocks such as plastic/swelling deformations of clay aggregates and the failure of rock inclusions through micro-crack growth are successfully replicated.
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    The Impact of Bedding Plane on Geotechnical Properties and Fractures Geometry of Montney Equivalent Outcrop Rocks
    (2023-01-03) Tabatabaei Poudeh, Seyed Hossein; Priest, Jeffrey Alan; Pedersen, Per Kent; Wong, Ron Chik-Kwong
    Hydraulic fracturing (HF) or fracking is extensively used to increase the permeability of unconventional source rocks, such as the Montney Formation which is a prolific producer of oil and gas in Western Canada. Optimizing the economic recovery of hydrocarbons in these reservoirs is dependent on understanding how the rocks fail. During HF, it is generally assumed that vertical fractures in the rock occur, since fracture propagate perpendicular to direction of minimum stress, which in the subsurface is typically in the horizontal direction. However, recent studies have shown that horizontal fractures are also formed as a part of the hydraulic fracture network (HFN), which is assumed to be related to weak bedding planes. To investigate the potential influence of weak bedding planes, a series of Brazilian tests were conducted on Montney equivalent outcrop rock samples. In these tests axial load is applied at different orientations to the bedding plane of the rock samples to evaluate the influence of bedding plane orientation on fracture behaviour, including Brazilian tensile strength, elastic properties and fracture propagation in micro and macro scale. The results of this study can lead to better understanding of the fracture behaviour of Montney siltstone and may help better predict HF fracture propagation and enhance hydrocarbon recovery.
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    An Integrated Variable Speed Limit with Dynamic Hard Shoulder Running for Urban Freeway Traffic Control
    (2018-01-12) Arora, Karan; Kattan, Lina; Wirasinghe, Sumedha Chandana; Priest, Jeffrey Alan; De Barros, Alexandre Gomes
    Many urban road transportation systems currently face serious problems regarding safety, along with issues of capacity shortage and unreliability. These factors not only have a local and direct effect on the transportation system in any city, but cause the inefficient use of fuels and as a result environmental pollution. To successfully manage congestion and safety issues using only the existing infrastructure, there is a need for efficient and dynamic traffic management strategies. This thesis introduces a novel dynamic control strategy, which includes the dynamic use of a proactive Variable Speed Limit (VSL) integrated with the dynamic use of Hard Shoulder Running (HSR) and in which both VSL and HSR would be proactively triggered. The “dynamic” nature of this strategy would allow for the optimum utilization of the existing roadway network. Whereas, the “proactive” nature of the trigger would allow for necessary control measures to be taken in advance to avoid the formation of a bottleneck. For traffic prediction, a modified METANET model has been developed which takes into consideration the complex nature of driver’s behavior along with driver’s compliance, capacity drop and posted speed limits. The modified METANET model is more efficient than conventional macroscopic prediction models in detecting the traffic congestions. This dynamic and proactive strategy was tested on Deerfoot Trail using exclusively developed integrated VISSIM-COM-MATLAB interface. A detailed comparison between No VSL, VSL only and VSL-HSR control strategy has been made. Both VSL only and VSL-HSR control strategy were effective in improving the overall network performance. Importantly, VSL-HSR control strategy outperformed the VSL only strategy. The results from this study suggested that with VSL-HSR control strategy, there was a significant increase in both the average speed, by 21.09%, and in vehicle-throughput, by 33.44%. Furthermore, there was a noticeable reduction in the average travel time by 39.98% and in the total number of stops, by 32.43%. Importantly, the safety analysis performed using Surrogate Safety Assessment Model (SSAM) revealed a marked reduction in collisions, by 29.73%.
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    The Stochastic Characterization of Natural and Hydraulic Fractures in Unconventional Reservoirs
    (2023-01-13) McKean, Scott Harold; Dettmer, Jan; Priest, Jeffrey Alan; Eaton, David WS; Wan, Richard G; Davidsen, Joern; Dusseault, Maurice Bernard
    An informed understanding of the subsurface is critical for mining, tunnelling, wastewater injection, carbon sequestration, and hydraulic fracturing (HF). Unfortunately, subsurface characterization is full of uncertainty. This is especially true when trying to understand or mitigate induced seismicity (IS), or the triggering of earthquakes by anthropogenic processes. This research focuses on hydraulic fracturing caused IS in unconventional reservoirs. The interaction between HF and IS is complicated by geomechanical variability and the presence of natural fractures. Our research accomplishes three objectives. We study natural fractures through outcrop analogues, discrete fracture network modelling, and induced seismicity. We characterise geomechanical rock properties along with their uncertainty. Finally, we develop a repeatable and scalable workflow to separate HF microseismicity from IS in order to characterise hydraulic and natural fractures. The research focuses on the Duvernay Formation in the Western Canadian Sedimentary Basin. An alpine outcrop equivalent of the Duvernay is characterized to quantify small- and large-scale fractures. This study reveals irreducible small-scale heterogeneity, as well as discernable patterns in large-scale fractures. Statistics and geostatistics are used to investigate elastic moduli and brittleness. The work shows how measurement and modelling uncertainity can propogate from laboratory to basin-scale. It reveals fundamental differences between elastic moduli and brittleness and shows why holistic modelling and uncertainty quantification approaches are essential to understanding and modelling the subsurface. We then introduce methods for the separation of HF microseismicity from IS. Physics-based clustering and Bayesian inference of diffusivity are used for the separation. This permits HF characterization which highlights the large variability of diffusivity and HF dimensions. We show why physics-based constraints are essential for microseismic analysis. The separated IS allows us to infer information about the natural fractures linked with induced seismicity. Application of the methods to the Duvernay shows HFs propogating directly into natural fractures and rotating away from the maximum principal stress direction towards natural fractures. Discrete fracture network modelling and parameter estimation is able to constrain the architecture of multiple fracture sets. We demonstrate that aseismic fracture sets are essential for establishing pressure connectivity and displaying IS.
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    Structural Behaviour of Spatial Arch Bridges
    (2017) Hudecek, Martin; Shrive, Nigel Graham; Sparling, Bruce; El-Hacha, Raafat; Sudak, Leszek Jozef; Wong, Ron Chik-Kwong; Priest, Jeffrey Alan
    This thesis investigates particular aspects of the structural behaviour of a new form of bridge structure called spatial arch bridge (SAB). SABs are designed to be outstanding pieces of architecture. Due to the enhancement in graphical and structural analysis software, the number of SABs is increasing. However, the complexity of SABs results in certain challenges in structural analysis and design. The unique combination of the arch, hangers, and deck result in the development of out-of-plane loads that significantly influence the structural response. This work focuses on SABs with an inferior deck suspended on flexible hangers (cables) below the arch. Three different spatial arrangements of the arch and deck are developed and analyzed to fill particular gaps in the current state of knowledge. Finite element analysis (FEA) is employed as the main analysis tool. Both linear and nonlinear parametric models are developed to address the objectives of the research. Ratios of primary and secondary geometric variables including arch rise, span, deck reach, and inclination or rotation of the parabolic arch are established to identify the trends in the structural response and to consider the effects of various types of loads. The significance of variability in the bending stiffness of the arch and the deck is studied to determine the optimal combination of these parameters that results in spatial configurations with minimal susceptibility to buckling as a function of particular types of end conditions of the deck. The work describes aspects of advanced composite materials (ACM), such as a low modulus of elasticity and time-dependent material properties in all-composite assemblies, and determines the applicability of commonly used durable structural profiles in SABs taking into account the nonlinear character of the cables and the effect of additional tensioning of the cables. The results of the large number of analyses conducted are summarized in tables accompanied with charts and schematic sketches that are intended to serve as guidelines when analyzing or designing structures similar in nature to the ones described in this work. Design criteria are proposed.