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oa Geophysics for Rock Properties and Material Separation during Dredging and Expansion of the New York and New Jersey Harbors
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 24rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Apr 2011, cp-247-00138
Abstract
The US Army Corps of Engineers and the Port Authority of New York and New Jersey are deepening 26 miles of navigation channels of New York harbor from -40 to -50ft MLW. the project requires dredging 50 million cubic yards of rock and sediment. At the halfway point, the project was ahead of schedule and under the US$1.6 billion budget.<br>Two key difficulties in the project are: (1) contaminated sediments and (2) undiggable rock. the cost of removing and placing contaminated black silt is 7 times the cost of removing and placing clean sands and silts. the cost of blasting and removing undiggable rock is 10 times the cost of removing sands and silts.<br>We have mapped the geology and the physical properties of the rocks and sediments throughout the project. All data, maps, and cross-sections are compiled into a single reference frame. All measurements are integrated in the Interpretation. the maps and cross-sections constitute the primary Information for managing the construction and engineering of the harbor deepening project.<br>We have developed geophysical techniques and operate them daily to determine the top-of-rock and to map and quantify the properties of the sediment, rock strata and quantify the area and thickness of black silt. Our techniques include calibration with core borings. Orthosonography yields aerial-photograph-like maps of the areal extent. Subbottom-seismic images, which are depth migrated, profile the thickness of the black silt and the approximate depth to undiggable rock. the black silt demonstrates anomalous properties and behavior from gray silt and other sediments. All images are georeferenced. We interpret the seismic sections through selection of horizons and estimation of physical properties. the seismic properties are correlated with mechanical properties to estimate diggability. the results are calibrated with core borings. We present the results as geological and geotechnical cross-sections with core borings. <br>Careful application of geology and geophysics to the New York Harbor Deepening Project allows for reduced uncertainty, improved project management, better planning, and reduced costs.