Degree

Doctor of Philosophy (PhD)

Department

Civil and Environmental

Document Type

Dissertation

Abstract

The long-term stability of offshore dredge pits is critical to the sustainability of coastal restoration efforts, particularly in sediment-starved regions like the northern Gulf of Mexico. Among the most promising sand sources for Louisiana's barrier island restoration are buried paleo-river channels known as mud-capped dredge pits (MCDPs), which are capped by cohesive mud and subjected to dynamic coastal conditions. While previous studies have focused on the morphological evolution of these features, limited research has investigated the geotechnical behavior of infilled sediments and their implications for slope stability and offshore infrastructure. This dissertation provides recommendations for the stability of the offshore pipeline at the MCDPs by addressing several key knowledge gaps by: (1) evaluating the geotechnical properties of MCDPs at Raccoon Island and Peveto Channel on middle and western Louisiana shelf, (2) investigating the effects of sand content on the undrained shear strength of mixed sediments, (3) characterizing wave-induced pore water pressure using long-term in-situ sensor deployments in an interdistributary bay, East Bay of Mississippi Delta, and (4) conducting inverse slope stability analysis of a wall failure at the Sandy Point MCDP on eastern Louisiana shelf near Mississippi Delta. Field data, laboratory testing, and numerical modeling are integrated to quantify physical and mechanical behavior, analyze failure mechanisms, and assess risks associated with sediment infill and hydrodynamic loading. Results reveal that infilled sediments exhibit lower shear strength and are significantly more prone to upheaval buckling compared to the surrounding continental shelf sediments due to their low effective unit weight and underconsolidated state. Based on consolidation test data and observed pore pressure dissipation rates, the infilled sediments are expected to reach near-equilibrium consolidation within approximately 10 to 15 years, depending on sediment composition and site-specific conditions. The undrained shear strength behavior of the mixed sediments aligns with the

Date

5-20-2025

Committee Chair

Celalettin Ozdemir

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Available for download on Tuesday, May 18, 2032

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