Coring for the Corps: The world’s largest public engineering agency, the U.S. Army Corps of Engineers (USACE), has three broad missions: military programs, support for agencies, and civil works. Some aspects of the civil works mission are flood control, shoreline protection, and navigation maintenance and improvement. Part of the USACE’s navigation maintenance responsibilities is the planning, permitting, and execution of dredging projects in national waterways.
The USACE, New England District is the lead agency for the proposed Providence River and Harbor Maintenance Dredging Project in Rhode Island, the purpose of which is to restore navigation efficiency and safety by restoring a channel depth of 40 feet below mean low water. A Draft Environmental Impact Statement (DEIS) for the project included the disposal option of a Confined Aquatic Disposal site for dredged sediments that are unsuitable for open-water disposal, and open-water disposal for the remainder of the material. Public comment asked for significant additional testing and modeling to complete the evaluation of the open-water disposal option for the Final Environmental Impact Statement (FEIS). In support of the FEIS, the New England District asked the USACE Waterway Experiment Station (WES) to assess erosion and consolidation of dredged material at the potential disposal sites. The consolidation and erosion studies performed by WES required long, rectangular cores undisturbed in terms of consolidation. The problem: How to collect undisturbed samples of sediment from the dredging area beneath more than 30 feet of water? Battelle, under contract with the USACE, proposed an innovative two part solution. First, modify an existing box corer to obtain samples to the appropriate depth. Second, design secondary push corers to collect the undisturbed cores from the box corer sample once on deck. The first step was the redesign of a Sandia Mark III box corer. A stainless steel extension was welded to the top of the box, extending its length to 38 inches. The spade arm swivel radius was then altered to allow the spade to properly close over the bottom of the core. Changes also had to be made to the box corer handling system on the survey vessel for safe deployment of the modified apparatus. All of the modifications were designed to be easily removed, allowing the box corer to be used in its original capacity. A push corer system was then designed to collect the subcores. A stainless steel push-coring device holds a push corer of Plexiglas and steel as it is inserted into sediment contained within the modified box corer. When the Plexiglas corer is fully inserted, a mechanical arm assembly seals the bottom of the core, allowing the extraction of a relatively undisturbed subcore. Roughly six weeks after engineering commenced, the innovative system passed field tests and sampling began. Sampling was conducted at nine stations in the Providence River. For each sample a box core was obtained. After retrieval of the box corer onto the boat, a rectangular push core was collected using the subcoring system. Each push core was sealed immediately after collection, labeled, and stored upright. Battelle personnel transported the samples to a flume facility at Georgia Tech for testing. A frame designed by Battelle specifically for this project was used to keep cores upright during transit. For more information about Battelle’s support of the New England District, please contact Karen Foster at (781) 952-5370 or via e-mail at foster@battelle.org.
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