Reinforced pipe provides strong foundation for Peace Project
Plans are underway to construct permanent headquarters for the U.S. Institute of Peace (USIP), which is scheduled for completion by the first quarter of 2010. The USIP was established in 1986 by the U.S. Congress, which provided $100 million to construct the institute’s new headquarters in Washington, D.C. The new facility will be located at the northwest corner of the National Mall, facing the Lincoln Memorial and adjacent to the Korean War and Vietnam Veterans memorials.
Prior to groundbreaking, the U.S. Institute of Peace Sewer Rehabilitation Project will involve shoring the existing infrastructure and ensuring structural integrity of the existing brick sewer that is located under the proposed building site.
Reportedly built in 1896, the brick sewer was assessed to be in fair condition, but planners decided that permanent preservation of the sewer should support future construction on the site. Construction plans were spearheaded by the District of Columbia’s Water and Sewer Authority, DCWASA, which is charged with ensuring reliability of the area’s infrastructure. In all, the DCWASA operates 1,800 miles of sewers and provides retail water and wastewater services to customers throughout Washington, D.C.
Slipline rehabilitation progresses
To evaluate existing site conditions as well as building proposals for the USIP headquarters, the DCWASA selected Metcalf & Eddy, a Washington, D.C.-based engineering firm. Engineers recommended that slipline rehabilitation was necessary to ensure that the existing sewer would not interfere with the future USIP facility. With sliplining, a new pipe is inserted into the existing pipeline to enhance structural integrity of the infrastructure. The new pipe liner has a smaller diameter than the old pipe to fit inside the established pipeline. A main benefit of this method is that minimal excavation is required for pipe insertion and connection. For the Peace Project, engineers recommended that the sliplining method had to be structurally sound, grouted in place and capable of handling the final loads. Fitting the bill was centrifugally cast, fiberglass-reinforced, polymer mortar (CCFRPM) pipe, made by Houston-based Hobas Pipe USA. The pipe combines high strength with a thin wall.
Construction crews sliplined the existing brick sewer with 360 linear ft. of 69-in.-diameter CCFRPM pipe. The actual inside diameter of the original brick sewer varied from location to location, but generally spanned 73 to 75 ins. The radial clearance calculated between the outside diameter of CCFRPM pipe and the inside diameter of the original brick pipe ranged between 0.25 and 1.25 ins.
Flush bell spigots were used as pipe connectors to provide a tight fit with the original pipe and ensure maximum flow recovery.
Capacity of the existing sewer in the sliplined area ranged from 103 to 119 million gallons per day (MGD), while capacity after rehabilitation was calculated to be 101 MGD. By using Hobas pipe, flow depths were lowered by approximately 10 to 20%.
Positive results seal the deal
Charlotte, N.C.-based Hall Contracting was called in to serve as a subcontractor for the sliplining operation. “The sliplining went very well,” said K. Michael Hall, CEO of Hall Contracting. “After the pipe insertion, we grouted the annular space ourselves with a lightweight grout, and this also went very well. The inspection ports revealed that the grouting filled the annulus completely. Three ports were installed at the 12 o’clock position, spaced evenly along the 330-ft. run. Upon inspection, the ports were solid with grout. We removed the valves and replaced the tapped holes with 1.5-in. PVC plugs.”
Sewer work is complete for the Peace Project, which now will advance to building the headquarters on a structurally sound infrastructure.
Hobas pipe is manufactured in sizes from 18 to 110 ins. in diameter. Both pressure and non-pressure pipe classes are available for a range of applications. Hobas Pipe USA, Houston, TX