In 1986, the United States Congress established the United States Institute of Peace (USIP), and provided $100 million for construction of a permanent headquarters facility in Washington, D.C. Finally being realized today, the edifice 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 ambitious 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. This process, dubbed the "United States Institute of Peace Sewer Rehabilitation Project," was charged with ensuring structural integrity to the existing brick-lined sewer, located under the proposed building site.

Structural requirements

As a 20-foot section of Hobas pipe is lowered into the excavation, the Lincoln Memorial can be seen in the background.

The District of Columbia's water and sewer authority, DCWASA, was given the task of ensuring reliability of the area's infrastructure, including a brick sewer, reportedly built in 1896, that had 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.

The planners also decided that slipline rehabilitation was necessary to ensure the sewer would not interfere with the future USIP facility. A centrifugally cast, fiberglass reinforced, polymer mortar (CCFRPM) pipe met all of the project requirements listed by the authority.

The approximate ground profile was 40 feet above the top of the existing sewer. Depending on which of the final designs for the USIP building was adopted, the proposed lowest level of the slab could have been as near as 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.

Preserving capacity

The USIP has provided this architect's rendering of its permanent headquarters building project. (Photo courtesy of United States Institute of Peace, Washington, D.C.)

The existing brick sewer was sliplined with 360 linear feet of 69-inch diameter CCFRPM pipe from Hobas Pipe USA, based in Houston. The actual inside diameter of the original brick sewer varied from location to location, but was generally 73 to 75 inches. The engineering firm thoroughly evaluated the host pipe conditions in order to maximize the diameter of the sliplining pipe. The radial clearance calculated between the pipe OD and the brick host pipe ID ranged between 0.25 and 1.25 inches.

The capacity of the existing sewer in the area that was relined ranged from 103 to 119 MGD, while the capacity after rehabilitation was calculated to be 101 MGD. Flow monitoring after rehabilitation on previously installed projects showed a Manning's roughness coefficient value of 0.009 to about 0.011.

Contracting CEO K. Michael Hall said, "It appeared from our post TV run that the flow depths had indeed been lowered by some 10 to 20 percent."

Slipped in easy

The brick construction of existing 19th century sewer was visible during the sliplining rehabilitation project for the proposed USIP building in Washington, D.C.

"The sliplining went very well," said Hall, "and 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-foot run. Upon inspection, the ports were solid with grout. We removed the valves and replaced the tapped holes with 1½-inch PVC plugs." PE