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

PPT Presentation

Pdf Summary

The Living Breakwaters Project is a mile-long green infrastructure initiative at the southern tip of Staten Island, New York. Funded by HUD and New York State, it was developed after Hurricane Sandy to reduce storm damage, address beach erosion, support marine habitats, and improve the shoreline experience. Construction was completed in 2024.<br /><br />The project includes 2,400 feet of intermittent, partially submerged breakwaters located 700 to 1,800 feet offshore. Structures combine linear trunks, roundheads, and selected “reef ridges” designed to encourage marine life. Subsurface investigations revealed soft, compressible soils up to 80 feet deep in the west, prompting changes to the layout, and varied layers of sand, silt, clay, and gravel elsewhere.<br /><br />Geotechnical design focused on bearing capacity, settlement, and global stability. Long-term consolidation settlement reached as much as one foot at one breakwater, so the design included overbuilding and monitoring. Static and pseudostatic stability were not critical, but post-earthquake conditions and dynamic wave loading required careful analysis. Tide levels, pore pressures, and wave-induced pressure differences influenced stability, particularly near low tide and the seaward toe.<br /><br />Construction challenges centered on marine mattresses: rock-filled geogrid containers used as base layers. Filled mattresses can distort, adjacent units may leave gaps, and equipment can damage the upper geogrid. The project addressed these issues through dimensional allowances, underwater inspections, gap filling, repairs, and protective measures. Curved roundheads required tailored mattress details, while seabed geotextiles needed installation tolerances for unavoidable wrinkles.<br /><br />Key lessons include agreeing early on acceptable seismic risk when design standards are limited, accounting for tidal and wave effects in stability analyses, and anticipating marine mattress irregularities during design. The upper geogrid should not be relied on for structural strength, and geotextiles should be protected during stone placement.

Keywords

Living Breakwaters Project

Staten Island

green infrastructure

Hurricane Sandy

breakwaters

marine habitats

geotechnical design

marine mattresses

shoreline erosion

wave stability