Digital Commons Network^™

Controls On Phosphorus Export From An Agricultural Watershed: Amsden Brook, Fort Fairfield, Maine Usa., Gregory J. Mcdonald

Electronic Theses and Dissertations

This study explores the sources and mechanisms of phosphorus (P) mobilization during base flow within the Amsden Brook watershed, Fort Fairfield, Maine, USA. Amsden Brook is an agriculturally dominated watershed drained by a spring-fed and perennial first- to second-order stream. We characterized the P concentrations within the watershed to investigate connections between soils, stream sediment, surface water, and groundwater. Waters were monitored monthly during the 2017 snow-free period for temperature, pH, dissolved oxygen, conductivity, soluble reactive P (SRP), total P, strong acid anions, strong base cations, dissolved organic carbon (DOC), Al, Fe, and Mn. Phosphorus speciation within soils and sediment …

Three-Dimensional Bedrock Channel Evolution With Smoothed Particle Hydrodynamics, Nick Richmond

Electronic Theses and Dissertations

Bedrock channels are responsible for balancing and communicating tectonic and climatic signals across landscapes, but it is difficult and dangerous to observe and measure the flows responsible for removing weakly-attached blocks of bedrock from the channel boundary. Consequently, quantitative descriptions of the dynamics of bedrock removal are scarce. Detailed numerical simulation of violent flows in three dimensions has been historically challenging due to technological limitations, but advances in computational fluid dynamics aided by high-performance computing have made it practical to generate approximate solutions to the governing equations of fluid dynamics. From these numerical solutions we gain detailed knowledge of the …

Development Of Thermoplastic Composite Reinforced Ultra-High Performance Concrete Panels For Impact Resistance, Reagan M. Smith Gillis

Electronic Theses and Dissertations

Recent studies investigating the impact performance of ultra-high performance concrete (UHPC) reported a quasi-brittle flexural failure that transitioned to a brittle punching-shear failure as the size of the impact head was reduced. A potential technology to increase the flexural strength and impact resistance of concrete is applying fiber reinforced polymer (FRP) composites to the exterior faces of the beam or slab. In this work, E-glass fiber reinforced thermoplastics were utilized in two different systems to apply reinforcement to UHPC. Thermoplastic materials were chosen over traditional thermoset materials for their unique advantages, such as rapid fabrication, automated manufacturing and the ability …

Field Implementation Of Tire Derived Aggregate As Lightweight Backfill For Retaining Walls, Jeremy Labbe

Electronic Theses and Dissertations

The objective of this study was to determine the effectiveness of Tire Derived Aggregate (TDA) as embankment and retaining wall backfill material using data from two field projects supplemented by data from previously published studies. Data collected from the two projects included horizontal earth pressure, resultant forces and moments acting in the wall stem, tensile and compressive forces within the wall, moments at the base of the wall, settlement of the TDA, time dependent temperature fluctuations within TDA, pore pressure changes in underlying foundation soil, movement of the wall face, and movement of the embankment. Data Collection was completed by …

Modeling Coastal Flooding And Sand Transport In The Gulf Of Maine During Severe Storms In A Changing Climate, Dongmei Xie

Electronic Theses and Dissertations

Elevated water level and large waves cause extensive damage and economic loss to coastal communities. An integrated atmosphere-ocean-coast modeling system that links physical processes with scales ranging from the open ocean to the surf zone has been developed for the Gulf of Maine. The modeling system includes a hydrodynamic model, a wave overtopping model and a sediment transport model. It is then applied to investigate and gain a comprehensive understanding of the following coastal processes: (1) the interaction between tide-surge, waves and bathymetry, (2) coastal flooding due to wave overtopping, and (3) sand transport.

Both coastal flooding and sand transport …

The Dynamics Of Mixing And Subtidal Flow In A Maine Estuary, Kristopher Bears

Electronic Theses and Dissertations

Long-term material transport in estuaries is largely controlled by subtidal flow. Subtidal flows are driven by conditions specific to their geographic location, namely river discharge, tidal forcing, and wind. These conditions are further modified by mixing, curvature of the estuary, Coriolis, and friction. While many practices of measuring these various forcing mechanisms exist, the current literature fails to provide a standard for measuring turbulent mixing in well- mixed estuaries. As a changing climate affects these various forcing and modifying mechanisms via sea level rise and increased precipitation, the corresponding material transport scheme is expected to change accordingly. Subtidal flow and …

Evaluation Of Non-Composite Steel Girder Bridges Using Field Load Testing And A Calibrated Finite-Element Model, Mahmood J. Albraheemi

Electronic Theses and Dissertations

This research focuses on understanding the behavior of five, non-composite, simple-span steel girder bridges using field load testing and calibrated finite element models. These bridges were tested during the summer of 2016. Strains and selected displacements were measured at multiple locations during the field load tests. 3D finite-element (FE) models were created to simulate the actual response of these bridges with a novel approach to calibrate these models was developed that captures the observed full and partial composite action as well as rotational restraint of the girder ends. More accurate predictions of the bridges capacity were determined using field tests. …