Geotechnical Aspects of Design & Construction for the Living Breakwaters Project-Paper

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The Living Breakwaters project comprises eight partially submerged rubble-mound structures along Staten Island’s south shore. Together, they extend about 2,400 feet and are intended to reduce storm-wave impacts and erosion while creating marine habitat.<br /><br />Geotechnical investigations found predominantly sandy seabed soils, with localized soft, compressible clay, particularly near Breakwater 1. Design analyses addressed bearing capacity, settlement, and global slope stability under static, seismic, liquefaction, and storm-wave conditions. The most demanding cases involved extreme waves and post-earthquake soil conditions. Analyses incorporated wave-induced pore pressures, sea-level rise, and potential scour. Geotextile reinforcement and geogrid extensions were important to achieving required stability, although low-friction interfaces between these materials also created potential failure paths. Predicted immediate settlements were generally manageable; Breakwater 1 was designed higher to accommodate long-term consolidation.<br /><br />Construction involved placing stone by barge and crane, with marine mattresses or geotextile forming the base beneath some structures. Field challenges included mattress distortion and gaps, geogrid damage, and wrinkles in underwater geotextile. The team addressed these through additional analyses, installation tolerances, repairs, inspections, and design adjustments.<br /><br />Key lessons include accounting carefully for wave and tidal effects, agreeing on seismic risk criteria early, and evaluating friction at interfaces between geosynthetics. Designs should also anticipate irregular mattress dimensions, gaps, curved-section fit, and installation-related damage. Overall, a flexible design that accommodates reasonable construction variations, supported by close coordination among project stakeholders, was central to the project’s success.

Keywords

Living Breakwaters

Staten Island

storm-wave attenuation

coastal erosion

marine habitat

geotechnical analysis

slope stability

geotextile reinforcement

liquefaction

seismic design