Design of a Confined Disposal Facility on Compressible Organic Soil

Abstract

In an effort to solve challenges associated with the maintenance dredging of its facilities, the Brooklyn Navy Yard Development Corporation in Brooklyn, New York (BNYDC) initiated the development of a nearshore confined disposal facility (CDF) for its navigational dredged material. When constructed, the CDF will provide capacity for the disposal of dredged material while simultaneously reclaiming approximately 1.5 hectares of developable land for BNYDC. The perimeter of the CDF site, the Wallabout Channel Barge Basin, is formed on three sides by low-level timber pile supported relieving platforms. The platform forming the northern boundary of the basin also supports an active concrete box sewer with an outfall located just beyond the limits of the proposed CDF closure structure. The platform along the eastern boundary of the basin carries an active roadway that serves as an entrance to the Brooklyn Navy Yard. Based on the findings of geotechnical investigations, two closure structure types were considered for the CDF: a linear master-pile type system, and a cellular sheetpile cofferdam structure. Conceptual designs and cost estimates for both systems were evaluated, and the master-pile system was selected for design. Closure structure design was complicated by the combination of high active pressures created by the dredged fill to be placed in the CDF; low passive resistance from the thick layer of existing organic materials; and the depth to competent soils at the site. The nature of the existing soft material in the Barge Basin, and that of the dredged fill to be placed in the CDF, would cause settlements due to consolidation in the range of 2 to 3 meters over a 50-year period, which would impose additional load on the existing structures, potentially resulting in their failure. This paper addresses the evaluation of protection of the existing structures versus their demolition, design of the CDF closure structure and implementation of ground improvement techniques to reduce time of settlement from 50 years to 5 years, thereby expediting utilization of the reclaimed land.