This study is an evaluation of Post Closure Care (PCC) duration of landfills using performance based methodology. The post closure care phase begins once the landfill is closed. As required by the Resource Conservation Recovery Act (RCRA) Subtitle D, PCC duration for municipal solid waste landfills is 30 years. During the PCC period, the landfill operator/owner is required to conduct monitoring for leachate, landfill gas, and ground-water and maintain the integrity of the cap so that the landfill does not impose a threat to surrounding human health and environment (HH&E). The duration of PCC can be reduced by the director of an approved State if an owner/operator of a landfill demonstrates that the landfill exhibits no threat to the surrounding HH&E or can be increased if the director of the approved State determines that an increased PCC period is required for the protection of HH&E. RCRA provides flexibility in optimizing PCC duration of landfills, although it does not identify the criteria/methodology which can be used in demonstrating the status of a landfill from the point of PCC. Researchers worldwide recognize that the threat imposed by a landfill after closure depends on the extent of degradation occurring inside the landfill. The increased functional stability of landfills reduces its risk to the surrounding HH&E. However, there is a wide range of opinions in defining functional stability of a landfill. The present thesis applies performance based methodology, developed by Environmental Research and Education Foundation (EREF), to making a decision on the PCC of landfills. Performance based methodology is a modular approach encompassing all four PCC components of landfills (Leachate, gas, groundwater and cap maintenance). This methodology was applied to Alachua County Southwest Landfill (ACSWLF) in Alachua County, Florida. Each module was analyzed individually and recommendations on the PCC monitoring at the landfill site were provided.

Yes / Formation of cracks represents one of the major causes of concrete deterioration, which can lead to durability and safety issues. In this work, a novel crack closure system is developed, using polyethylene terephthalate (PET) polymer fibres embedded in a mortar mix. The PET polymer has shape memory properties and shrinks upon thermal activation, if free to do so, or otherwise exerts shrinkage restraint forces. A single knot was manufactured at each end of the PET fibres to provide mechanical anchorage into the mortar matrix. Mortar samples with embedded knotted fibres were pre-cracked and subsequently placed in an oven to thermally activate the polymers and induce the shrinkage mechanism into the fibres. Crack closure was measured in the range 45–100%, depending on the geometry, dimension and distribution of the fibres, and the size of the initial crack. / This work is supported by UKRI-EPSRC (Grant No. EP/P02081X/1, Resilient Materials 4 Life, RM4L).

<p> This thesis demonstrates the effectiveness of matrix methods in algebraic number fields, the integral closure of pure cubic fields and the use of the Hessian and discriminant to determine integral closure. </p> / Thesis / Master of Science (MSc)

The use of moment-closure methods to predict continuum and moderately rarefied flow offers many modelling and numerical advantages over traditional methods. The maximum-entropy family of moment closures offers models described by hyperbolic systems of balance laws. In particular, the twenty-one moment model of the maximum-entropy hierarchy offers a hyperbolic treatment of viscous flows exhibiting heat transfer. This twenty-one moment model has the ability to provide accurate solutions where the Navier-Stokes equations lose physical validity due to the solution being too far from local equilibrium. Furthermore, its first-order hyperbolic nature offers the potential for improved numerical accuracy as well as a decreased sensitivity to mesh quality. Unfortunately, higher-order maximum-entropy closures cannot be expressed in closed form. The only known affordable option is to propose approximations. Previous approximations to the fourteen-moment maximum-entropy model have been proposed [McDonald and Torrilhon, 2014]. Although this fourteen-moment model also predicts viscous flow with heat transfer, the necessary moments to close the system renders it more difficult to approximate accurately than the twenty-one moment model. The proposed approximation for the fourteen-moment model also has realizable states for which hyperbolicity is lost. Unfortunately, the velocity distribution function associated with the twenty-one moment model is an exponential of a fourth-order polynomial. Such a function cannot be integrated in closed form, resulting in closing fluxes that can only be obtained through complex numerical methods. The goal of this work is to present a new approximation to the closing fluxes that respect the maximum-entropy philosophy as closely as possible. Preliminary results show that a proposed approximation is able to provide shock predictions that are in good agreement with the Boltzmann equation and surpassing the prediction of the Navier-Stokes equations. Furthermore, Couette flow results as well as lid-driven cavity flows are computed using a novel approach to Knudsen layer boundary conditions. A dispersion analysis as well as an investigation of the hyperbolicity of the model is also shown. The Couette flow results are compared against Navier-Stokes and the free-molecular analytical solutions for a varying Knudsen number, for which the twenty-one moment model show good agreement over the domain. The shock-tube problem is also computed for different Knudsen numbers. The results are compared with the one obtained by directly solving the BGK equation. Finally, the lid-driven cavity flow computed with the twenty-one moment model shows good agreement with the direct simulation Monte-Carlo (DSMC) solution.

Elastic-plastic finite element analyses were performed to predict the crack opening level profiles in semi-elliptical surface cracks. A script was written to use the commercial finite element code ANSYS to predict opening levels in cracked geometries. The functionality of the scripts was verified by comparing predicted opening levels in two and three-dimensional center-cracked geometries to experimental results. In addition, a parameter study was performed in which various aspects of the modeling routine were modified. This included a mesh refinement study as well as a study into the effect of a strain hardening material. The main focus of the current research, however, is to compare finite element predicted opening levels with published opening levels determined experimentally. Due to the complexities and long run-times involved with these models, no attempt was made at growing the cracks from initial length to final length. Instead, discrete crack lengths at which experimental opening levels were published were instead used. Also, no attempt was made to predict the crack aspect ratio evolution. The finite element predicted opening levels were in all cases significantly lower than those reported experimentally, however, similar trends in both crack opening level profile along the crack front, and opening level variations with crack growth were shown.

This thesis discusses the analysis of fatigue crack growth in the presence of residual stresses to determine a suitable method for fatigue life predictions. In the research discussed herein, the prediction methodologies are compared to determine the most accurate prediction technique. Finite element analysis results are presented as well as laboratory test data. The validity of each methodology is addressed and future work is proposed.

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