Department of Civil Engineering Graduate Theses

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    Mechanochemical Destruction of Per- and Polyfluoroalkyl Substances in Environmental Media by Planetary Ball Milling
    (2024-03-18) Turner, Lauren Paige; Civil Engineering; Kueper, Bernard; Weber, Kela
    Per- and polyfluoroalkyl substances (PFAS) are an abundant and diverse group of anthropogenic, fluorinated organic chemicals that are ubiquitous in the environment. PFAS can adsorb to soils through hydrophobic and electrostatic interactions, resulting in contaminated sites with high retention in soils. PFAS impacted soils can act as sources of exposure to humans or sources of contamination to groundwater. Due to human health concerns and increasingly protective regulations, there is a demand for destructive remedial technologies for PFAS-impacted soils. The objective of this work was to evaluate the destruction of PFAS in environmental solid media. Using a benchtop planetary ball mill with stainless steel grinding media and a 250 mL grinding jar, the remediation of PFAS-impacted media and aqueous film forming foam (AFFF)-impacted media by ball milling was studied. Results demonstrated that PFAS can be destroyed in single compound PFOS- or PFOA-amended sand, dual compound PFOS- and PFOA-amended silicates and carbonates and multi-compound AFFF-amended sand. Water content of media was a significant hinderance to PFOS and PFOA destruction, with most saturated trials resulting in negligible destruction. In 100% water saturated media, potassium hydroxide (KOH) as a co-milling reagent was effective at improving destruction up to 99% PFOS and 92% PFOA in amended nepheline syenite sand. KOH resulted in increased recovery of fluoride post-milling, suggesting improved defluorination or improved fluoride extraction in the presence of KOH. KOH as a co-milling reagent in AFFF-amended silica sand influenced perfluorocarboxylic acid (PFCA) transformation byproduct distribution. In diverse media, a range of PFAS were demonstrated to be destroyed without-KOH as a co-milling reagent, proving media and soil components can become reactive upon ball milling. It was identified that electrons are a reactive species generated from environmental media. High resolution mass spectrometry was employed to evaluate target and non-target transformation byproducts, and in combination with electron generation and fluoride measurements, results provided evidence to suggest an electron initiated reductive destruction mechanism, likely coupled with other pathways. Results from this work identified key factors to consider in applying ball milling for remediation and suggest further study and scale up should be explored.
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    Physical Modelling of Instability in Granular Soils and Tsunami Hazards Associated with Coastal Slope Failures
    Treflik-Body, Erica J.; Civil Engineering; Take, Andy; Mulligan, Ryan; Steel , Elisabeth
    Coastal mass failures such as submarine and subaerial landslides have the potential to create significant tsunami hazards. As an inherently coupled solid-fluid interaction problem, accurate assessment of these hazards requires an understanding of the triggering mechanisms of failure to predict the consequential wave generation upon impact. With respect to triggering mechanics, failures of submarine slopes have been observed to occur at perplexingly low inclinations, which could be a result of soil instability. In this study, large-scale tilt table testing under dry and submerged conditions were conducted with imbedded shear stress and strain sensors to quantify the constitutive behaviour and pore pressure response of loosely placed sand leading up to and during instability. Multiple instability events were observed in the dry specimen whereas a single instability event at lower inclinations occurred for submerged samples at the same initial void ratio. The pore water pressure response following instability was consistent with the material coefficient of consolidation for liquified soils. Wave consequences were explored through large scale granular collapse experiments conducted with a new vertical lifting gate facility. Granular columns under varying levels of submergence were released and the wave generation, propagation and runup were captured through wave capacitance gauges and cameras. Both the seaward- and landward-directed waves associated with fully submerged failures were quantified. The observed seaward wave amplitudes agree with existing empirical relationships developed from small scale testing and a new analytical solution for the landward wave amplitude is presented. A sample of these large-scale tests were numerically simulated using a coupled DEM-LBM model, which adequately captured the landward and seaward wave characteristics and behaviours.
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    Bond Strength and Development Length of Sand-Coated GFRP Bars Spaced and Bundled in Normal Strength and Ultra-High-Performance Fibre-Reinforced Concrete
    Kaufman, Lukas J.; Civil Engineering; Fam, Amir
    This thesis experimentally examines the bond strength and development length (Ld) of three sand- coated glass fibre-reinforced polymer (GFRP) bar sizes (#4, 5 and 8) embedded into ultra-high- performance fibre-reinforced concrete (UHPFRC) with 2% steel fibres. It also examines the Ld of sand-coated #5 GFRP bars bundled in two and three embedded into normal strength concrete (NSC). Both studies followed the RILEM RC5 standard notched beam bond test method. For the first study investigating GFRP bars with three bar diameters (db), concrete cover (C) varied from 20 mm to 55 mm, and embedment lengths (Le) were 4db, 9db and 14db, totalling 42 notched beams. 38 of 42 beams failed by splitting bond failure. ACI CODE-440.11-22 significantly overestimated Ld by factors of 2.0 to 3.5. The Michaud et al. (2021) design equation for Ld does not account for C or db. As such, at lower C/db ratios (i.e. at small concrete covers), it underestimated Ld while at higher C/db ratios (i.e. at larger cover), it overestimated Ld. A new equation for Ld has been developed, accounting for all critical parameters. For the second study investigating #5 GFRP bars spaced and bundled in groups of two and three, a total of 12 notched beams were tested. Clear concrete cover was consistent at 40 mm, while Le varied from 17 to 87db. It was found that bundling bars reduced the maximum attained longitudinal tensile stress at bond failure by 18-31% for two bars and 24-36% for three bars. At the full design tensile strength (ffu), the Ld of bundles of two and three bars were 1.4 and 1.5 times larger, respectively, than spaced bars. As the tensile stress ratio (ff/ffu) reduced from 1.0 to 0.34 (as in compression controlled failure), the Ld of bundles increased up to 1.9 and 2.5 times the spaced bars, respectively. An expression for this variable bundling factor is proposed. ACI CODE-440.11- 22 also underestimated Ld of spaced bars at ffu by 33%. A correction factor of 1.5 is recommended for spaced sand-coated bars with no deformations when the code equation is used.
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    Influence of Geosynthetic Stiffness on Deterministic and Probabilistic Analyses of Reinforced Soil Structures with Focus on Reinforced Fills Over a Void
    Mahdavi Naftchali, Fahimeh; Civil Engineering; J. Bathurst, Richard
    Geosynthetic reinforcement products are rate-dependent polymeric materials meaning that they exhibit strain-, time- and temperature-dependent behaviour under load. In the vast majority of the geosynthetics literature, the load-strain-time properties of geosynthetic reinforcement materials are ignored in the analysis and design of geosynthetic reinforced soil structures under operational (serviceability) conditions such as mechanically stabilized earth (MSE) wall structures and reinforced fills over a void. One important outcome of this thesis is a large database of geosynthetic reinforcement properties for a wide range of products and product classifications with their rate-dependent behaviour described by a simple two-parameter hyperbolic isochronous model. This model is used to demonstrate the influence of reinforcement stiffness on the magnitude of MSE wall deformations and loads under operational conditions. However, the main focus of this thesis is to examine the influence of reinforcement stiffness on the reinforced fill over a void problem. Analytical methods for geosynthetic-reinforced fills over voids most often overlook the impact of geosynthetic reinforcement reduced stiffness due to creep during tensile loading. This thesis addresses this gap by introducing a reinforcement stiffness limit state for analysis and design of these systems together with the two-parameter hyperbolic isochronous load-strain model. A disadvantage of analytical solutions for the reinforced fill over a void problem is that the coupled effects of fill and reinforcement properties, and problem geometry are not considered. To overcome this deficiency, a 2D finite difference (FLAC) numerical model of the reinforced fill over a void is developed that implements the hyperbolic isochronous load-strain model for the reinforcement layer. This thesis shows how rate-dependent properties of polymeric reinforcement geosynthetics impact reinforcement tensile strains, load, and overall system performance. There is a movement in geotechnical engineering towards a probabilistic approach to performance-based design and quantification of limit state margins of safety in probabilistic terms. This thesis looks at margins of safety for selected limit states for the problem of a reinforced soil fill over a void from both a classical factor of safety point of view and, for the first time, from a reliability-based design (probabilistic) point of view.
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    Numerical Modelling Hydrodynamics and Sediment Dynamics of a Managed Realignment Site in the Bay of Fundy
    Burns, Rachel A.; Civil Engineering; Mulligan, Ryan
    Managed Realignment is a method of creating more coastal wetland environments, by breaching constructed dykes to allow seawater driven by tides to flood the land surface and enable re-establishment of salt marshes over time. To understand the development of the Converse managed realignment site along the Missaguash River in the northern Bay of Fundy, a numerical model with an unstructured flexible mesh (Delft3D-FM) was applied. First the hydrodynamics inside and around the breach before and after seawater flooding of the site were studied to evaluate the initial impacts of nature-based managed dyke realignment. The same model was then applied to study the sediment dynamics across the managed realignment site. Field observations of water levels and current velocities, suspended sediment concentrations and deposition were collected over 6 tidal cycles at spring tide in areas outside and around the flooded area. Results indicate that the breach in the dyke along the tidal channel was not wide enough to influence water levels within the channel, however current speeds of up to 1 ms-1 in the breach and 0.25 ms-1 across the flooded area with an average depth of 0.66 m promote sediment transport into the flooded area. With model results indicating that the tidally driven flows through the breach and the bathymetry of the flooded area play important roles in controlling flow speed and deposition patterns, the site acts as a sediment sink aligned with the early stages of salt marsh re-development. Overall, the findings in this study lay a foundation for further work of modelling salt marsh restoration projects across a hypertidal setting and contribute to a better understanding of the progress of managed realignment projects in the Bay of Fundy.