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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Civil and Environmental Engineering

Year Degree Awarded

2018

Month Degree Awarded

September

First Advisor

Don J. DeGroot

Second Advisor

Guoping Zhang

Third Advisor

Jonathan D. Woodruff

Subject Categories

Civil Engineering | Environmental Engineering | Geology | Geotechnical Engineering | Sedimentology | Urban Studies and Planning

Abstract

Erosion of silts and clays is less well understood than erosion of sands. Further, current and anticipated climate change impacts along coastlines compel consideration of new approaches to coastal protection measures; seawalls and breakwaters designs now include natural and nature-based measures.

The first research topic consists of the Adaptive Gradients Framework which was a theoretically-informed facilitation tool. The framework was intended to aid a collaborative and interdisciplinary decision-making process to encourage inclusion of natural and nature-based measures in coastal protection planning and design. This research is the culmination of a series of workshops and fieldtrips executed by the Sustainable Adaptive Gradients in the Coastal Environment (SAGE) network.

Biopolymers could prove an effective nature-based means of stabilizing the upper portion of soft clay. Therefore, the second phase of this research investigated changes in strength, micromorphology, and microstructure for a variety of soils amended by four biopolymers (xanthan gum, guar gum, carrageenan and dextran), and then used this information to infer biopolymer-soil interactions. Test methods included liquid limit (LL), fall cone (FC), and environmental scanning electron microscopy (ESEM). Fall cone results demonstrated both an immediate strength gain, and a time-dependent strength gain to the biopolymer-soil mixtures. Some of the biopolymers demonstrated a saturation point. Finally, the results showed that the guar and carrageenan behave fundamentally differently than xanthan and dextran. Advantages and limitations of different biopolymers were compared.

The final phase of research included design and construction of the UMass Amherst Flume (UMAF). The UMAF was built to observe erosion of very soft cohesive soils under varying tidal flow rates. Final design included an infrared sensor and sampling port. Computational fluid dynamics modeling was performed to quantify the applied stress of the fluid flow at the soil-water interface for varying speeds. The flume was validated through a series of laboratory tests including fine- and coarse-grained soils and biopolymer-soil mixtures. Results of this investigation indicate that soils with similar index properties and similar undrained shear strengths may erode at different critical erosion shear stresses. Results also indicate that biopolymers have the potential to increase critical erosion shear stress for very soft cohesive soils.

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