Sliplining a 110-year-old brick sewer shores the subsurface infrastructure for new U.S. Institute of Peace headquarters.
United States Institute of Peace Sewer Rehabilitation Project
In 1986, the U.S. Congress established The United States Institute of Peace (USIP) and has provided $100 million for construction of a permanent headquarters facility in Washington D.C. It 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.
Construction of the facility is scheduled for completion by the first quarter of 2010. However, there is a great deal of work to be done prior to groundbreaking. This includes shoring the existing infrastructure. The United States Institute of Peace Sewer Rehabilitation Project will ensure structural integrity to the existing brick sewer that is located under the proposed building site.
The 19th century brick sewer is visible during the sliplining rehabilitation project for the proposed USIP building in Washington, D.C.
The District of Columbia Water and Sewer Authority (DCWASA) operates 1,800 miles of sewers and provides retail water and wastewater services to its customers in the district. DCWASA is charged with ensuring reliability of the area’s infrastructure. A brick sewer that was reportedly built in 1896 has been serving the area. Although it was in fair condition, with only a few repairs required in recent years along its entire length, planners decided that it needed permanent preservation to support future construction.
DCWASA also decided that slipline rehabilitation was necessary to ensure the sewer would not interfere with the future USIP facility. HOBAS centrifugally cast, fiberglass reinforced, polymer mortar (CCFRPM) pipe was the only product that met all of the project requirements. The new CCFRPM sewer is structurally sound, leak free, and provides adequate capacity.
Pipe is lowered into an excavation for sliplining a circa 1896 brick sewer as part of the United States Institute of Peace Sewer Rehabilitation Project in Washington, D.C.
Randolph Rostas, senior project manager with Metcalf & Eddy (M&E), Washington, D.C., was design engineer for the project. Project manager was Naveen Krishnamurthy from M&E’s Baltimore, Md., office. Its engineers evaluated existing site conditions, as well as building proposals. The approximate ground profile is 40 feet above the top of the existing sewer. Depending on which of the final designs for the USIP building is adopted, the proposed lowest level of the slab could be just 5 feet above the existing sewer. Regardless of the final design, the pipe to be installed had to be structurally sound, grouted in place, and capable of handling the final loads.
The existing brick sewer was sliplined with 360 feet of 69-inch-diameter HOBAS CCFRPM pipe. The inside diameter of the original brick sewer varied from location to location but was generally 73 to 75 inches. M&E thoroughly evaluated the host pipe conditions to maximize the diameter of the sliplining pipe. The radial clearance calculated between the HOBAS pipe outside diameter and the brick host pipe inside diameter ranged between 0.25 and 1.25 inches.
HOBAS CCFRPM’s efficient cross-section provides high strength with a thin wall. HOBAS also offers many pipe diameter choices for this type of application, such as the 69-inch nominal diameter used in this project. The tight fit possible with the flush bell spigot pipe connectors also contributed to maximum flow recovery.
General contractor for the USIP project, Clark Construction Group, LLC, Bethesda, Md., brought Hall Contracting, Charlotte, N.C., onboard as the installation subcontractor for the sliplining operation. Hall had used HOBAS pipe on more than 10 past projects dating back to 1997. K. Michael Hall, CEO, noted, "Hall tackles tough, large-diameter slipline projects and has used HOBAS pipe almost exclusively due to its toughness and ease of installation. This job was no exception."
The capacity of the existing sewer in the area that was relined ranged from 103 to 119 million gallons per day (mgd), while the capacity after rehabilitation was calculated to be 101 mgd. Flow monitoring after rehabilitation on previously installed HOBAS projects showed a Manning’s value of 0.009 to about 0.011. Manning’s values in this range are commonly used to predict capacity after sliplining. "On this particular project, we designed the sewer utilizing a predicted Manning’s value of 0.011 for the HOBAS pipe," stated Rostas.
K. Michael Hall commented on the installation, "It appeared from our ’post TV run’ that the flow depths had indeed been lowered by some 10 to 20 percent."
"The sliplining went very well," said Hall, "and after the pipe insertion, we grouted the annular space ourselves with a lightweight grout, [which] also went very well. Inspection ports revealed that grouting filled the annulus completely. Three ports were installed at the 12 o’clock position, spaced evenly along the 330-foot run. Upon inspection, the ports were solid with grout. We removed the valves and replaced the tapped holes with 1½-inch PVC plugs." The plugs were provided by HOBAS.
Kimberly Paggioli, P.E., is marketing manager for HOBAS Pipe USA. She can be contacted at email@example.com.