PURCELLVILLE, VA. — Two sites at the Bethesda National Naval Medical Hospital are undergoing ground improvement by design-build contractor GeoStructures so that construction can start for buildings designated for the Warrior Transition program.
Beneath the designated area for Building 17, a multi-story administrative structure, the company is installing Rammed Aggregate Pier (RAP) elements to ensure the ground’s ability to support the building. With subsurface conditions showing bedrock at varying depths, the company designed a system with conventional RAPs, uplift RAPs, and tie-down anchors to handle the required loads. Similar to conventional RAPs built with compacted aggregate in one-foot lifts, uplift RAPs include a harness that anchors to footings as a way of providing resistance against uplift forces as a result of wind or seismic forces. The RAPs range in length from 8 to 28 feet.
The use of RAPs also contributed to material re-use credits in LEED, the green building certification system. The RAP construction technique incorporated concrete recovered from the demolition of a building onsite, which led to several environmental benefits: the concrete was crushed onsite, so there were no inbound truck shipments of new aggregate, no outbound hauling of old concrete, and no costs for land-filling the debris, thus limiting the carbon footprint of the overall project.
At the site for Building 62, also known as the Bachelor Enlisted Quarters and the Warrior Transition Unit Administration Center, conditions were similar with bedrock close to the surface in some areas and deeper in others. GeoStructures designed a system to accommodate the variations using RAPs to reinforce soils and to support spread footings for the structure, which will be comprised of three wings that wrap around an existing building. The RAPs here range in length from 8 to 21 feet.
“The overall challenge we faced was the different rock elevations, but with the design-build approach we could collaborate efficiently with the project design team to reach the right conclusions on system components and their overall design,” said Shana Opdyke, Mid-Atlantic sales and LEED-certified engineer for GeoStructures. “I also am proud that GeoStructures continues to deliver sustainable design-build solutions by re-using recycled, crushed concrete in RAP construction.”
Completion of these two buildings in August 2011 complies with the requirements of the Base Realignment and Closure mandate that is re-organizing the nation’s defense-related agencies and assets.