Development of a quantitative criteria for the Coastal Road Erosion Susceptibility Index (CRESI) armoring parameter using stability analyses of seawalls under ocean non-hazard and hazard loading conditions on Oahu, HI

Martinez, Brookks Anthony Ceria
Francis, Oceana P.
Civil Engineering
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Coastal roads across the State of Hawaii are most at risk to inundation and erosion from ocean hazards including waves, currents, tides and sea level rise. The Coastal Road Erosion Susceptibility Index was developed to prioritize management measures at certain coastal road segments (“transects”). However, the criteria assessing the contribution of armoring to erosion was greatly lacking in quantitative, objective descriptors. Therefore, this study proposed to improve criteria relating the condition and performance of a soil-retaining seawall, a specific type of armoring, to erosion susceptibility at the coastal transect which they are located within.A soil-structure’s ability to influence erosion susceptibility across the transect is based on its stability, quantified by factor of safety (FS), against gross active overturning caused by ocean hazard hydrostatic and hydrodynamic loads and earth pressures. Overturning is a condition that decreases its ability to buffer tides and waves from eroding the coastal land mass. The proposed improved criteria contains index FS ranges that describe various degrees of armoring stability. Greater FS indicates more stability and contributes to very low erosion susceptibility. Lesser FS indicates lesser stability and contributes to very high erosion susceptibility. Using site-specific ocean hazard, geometric, and geotechnical information, FS was back-calculated for multiple ocean hazard loading conditions. Three sub-criteria were proposed to account for stability under three distinct groups of ocean hazard loading conditions. Each transect considered in this study was assigned a total of eight scores, each representing their soil-structures’ stability against a specific ocean hazard load combination. Increasingly severe ocean hazard loads did not always result in higher erosion susceptibility, which would be reflected by lesser FS values in this study. Progressive ocean hazards caused FS to increase at some locations and decrease at others due to the unique combination of geometric characteristics present at each seawall considered in this study. The methodologies presented herein relating armoring stability to transect erosion susceptibility in this study may be applied to transects with similar soil-structure properties.
Civil engineering, armoring, erosion, ocean hazards, stability analysis
98 pages
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