Large diameter sewer pipe rehabilitation called for special techniques

The challenge of replacing deteriorating large diameter sewer pipes with no possibility of bypass was successfully met recently by the City of Evansville, Indiana.

When the City of Evansville, IN, recently needed to renew its large diameter sewers, it contracted with Hobas Pipe Company to rehabilitate more than two miles of 90 to 108-in. RCP combined sewer pipe, which was structurally deteriorated and leaking due to corrosion and open joints.

Since the pipes needed to remain in service, Hobas made plans to slipline live with 78 to 96-in. centrifugal cast fiberglass reinforced polymer mortar (CCFRPM0) pipes .

Threat of rain event prevented bypassing
The liner was needed to eliminate leakage, stop corrosion, maintain the flow capacity and restore the structural integrity of the sewers, which are up to 35 ft deep. Additionally, although the normal flow level was only 6 to 12 in., it was not possible to by-pass pump a rain event when flows would be substantially increased. This restriction dictated the "live" installation.

To meet all of these requirements, the specifications of designer, Rust Environmental and Infrastructure of Indianapolis, allowed only a sliplining installation of CCFRPM pipes with bell-spigot, gasket-sealed joints. Due to the Hobas pipes' low profile wall, the specified minimum diameters were actually exceeded by one to five inches, thereby assuring full flow recovery or, in several cases, increased capacity.

Insertion of liner went well
Because the project included five different diameters, lines on four separate streets, a PI and a curve, installer, Bowen Engineering of Fishers, IN utilized seven access shafts. The new liners were slid into the host pipes using an Akkerman built machine, without flow by-pass, plugging or diversion, in 13 discrete pushes at rates of 100 to 150 ft per hour. Five insertions were over 1000 ft with a longest single drive of 1400 ft. Despite the relatively low normal flows, the maximum push load was only 110 tons and most runs were completed with 60 to 90 tons.

Perhaps more important, no liner pipes were damaged. Most liner sections were 20 ft long, however, five foot pieces were used in the curve. Because of the turn severity, a few joints weren't fully homed. They were later sealed, in-place, with permanent interior laminations.

Unusually frequent laterals reconnected
Although frequent laterals are uncommon in pipes this large, these interceptors contained 105, ranging from 6 to 30 in. Forty, mostly 12 to 15 in., were reconnected by internal lamination of a PVC extension to the liner pipe. A new, shallower collection line was installed to capture the remaining 65. These flows were returned to the system at a manhole.

Grout filled in annular spaces
The installation was completed by filling the annular space between the host ID and liner OD with 40 pcf grout in one lift. Once again, no liner damage occurred and no pipes or joints leaked.

The success of this project is leading to a plan by the city to use the Hobas pipes again on an upcoming, new, open cut sewer installation.

For more information on this process and products, click Hobas Pipe

Edited by Joyce Everhart Jungclaus
Editor, Public Works Online
Source: Hobas Pipe USA, Inc.