Confronted with a deteriorated sanitary sewer routed deeply beneath several major roadways and a well-established residential area, the Baltimore County Department of Public Works opted for a relining program rather than replacement. A sizeable portion of the Long Quarter Outfall Rehabilitation Project involved placing 24-in.-diameter liner inside a deteriorated reinforced concrete main via slip lining.
As the relining process began, the contractor determined that the unusually close working conditions were best suited to segmental slip-lining pipes. Contech A2 liner pipe with gasketed joints was selected for the installation.
A2 liner is a lightweight, profile-wall, PVC segmental slip-lining pipe available in 10- or 20-ft lengths. The StabJoint coupling permits fast joining and provides a positive seal while fitting flush with the interior and exterior linear pipe surfaces for optimum internal flow and to prevent hang-ups on the host pipe during placement.
Although A2 liner can be installed without interrupting flow in the line, slip lining on this project was performed during short-duration pump station shutdowns.
“This was our first installation experience with A2 liner pipe, and it’s all the things we need: fast, easy and simple,” said the contractor’s project superintendent. “We achieved slip-lining rates approaching 200 ft per hour, which is remarkable performance”
Segmental slip-lining pipe, especially in 10-ft lengths, also permitted smaller insertion pits. Crews found that 14-ft pits were adequate, which meant they would spend less time on excavation and restoration. The lightweight liner pipe also eliminated concerns about construction loads on the existing sewer.
“We were able to complete the original relining project in approximately one-half of the 100-working-day time limit,” said the installer’s project manager. “One of the contributing factors was the switch to segmental slip-lining pipes. We installed approximately 1,400 linear ft of the 24-in. A2 liner product in the existing 27-in RCP lines. In addition to better-than-expected installation rates, the A2 liner passed the required air test on the first try.”