Honolulu utility rehabilitates a force main with CIPP liner
In 2014, Insituform completed a contract as a subcontractor to Hawaiian Dredging to rehabilitate a 65-ft-long section of 20-in. force main crossing one of the busiest intersections in the Waikiki area of Honolulu. Line breaks and concerns about the reliability and integrity of the nearly 50-year-old ductile iron force main resulted in the City and County of Honolulu requesting design for an emergency repair.
The force main exits the vault outside a wastewater pumping station and then crosses three lanes of a major thoroughfare in the Waikiki area. Traffic volumes on Kalakaua Avenue dictated limited working hours for nearly all aspects of the installation. The system configuration allowed the force main to be taken out of service for the duration of the rehabilitation project, with a parallel pipe conveying flow from the pumping station.
The city’s design engineer contacted Insituform to assess the use of a fiber-reinforced cured-in-place pipe (CIPP) pressure-rated liner, known as InsituMain, to carry out the rehabilitation. While Insituform has installed traditional CIPP on the island, this would be the first CIPP pressure pipe lining project. Insituform’s Oahu office, with support from its engineering and pressure pipe operations, provided reviews and comments on the liner design, installation and ancillary works required for the project.
One of the first tasks after the project was awarded was pipe excavation. This allowed inspection of the force main, confirmation of the inside and outside diameters and a CCTV inspection. These activities provided all the information required to order the liner material and vinyl ester resin, which is not commonly used in Hawaii.
The operating pressure for the force main was estimated to be about 35 psi, with a test pressure of 65 psi. To meet these and other design conditions, the InsituMain liner was designed to be 9.5 mm thick. The system used Hymax compression fitting to reconnect back into the existing system, eliminating any need for adhesion to the host pipe to ensure a watertight application.
Since Fort DeRussy borders Waikiki Beach, the pipe was within the groundwater zone and subject to tidal influences. This fluctuation in water level meant that all the fittings installed would be subject to additional corrosion considerations. To address this, all exposed bare metal components were covered with Trenton Wrap.
After Hawaiian Dredging provided the pipe cleaning, the liner was wet out (impregnated with resin) at Insituform’s facility on Oahu and then loaded into a reefer truck to transport to the job site for installation the following day. The installation method for these liners typically uses water head inversion, propelling the liner the length of the host pipe. A scaffold tower provided the necessary 23 ft of water head to invert and install the liner, which was then cured by heating and re-circulating water in the tube until the desired temperature was achieved and then finally allowed to cool.
The next day, the liner was drained, ends were cut and sizing rings were removed. A fast-setting resin was then applied to the exposed liner to smooth the surface, eliminating any rough areas that could impact the ability to achieve a proper seal with the Hymax couplings. The fittings and pressure test components were installed and then shored and braced in preparation for the pressure test.
During the course of the pressure test, weather forecasts predicted a significant storm for Oahu. The owner decided that the force main should be made available for immediate use to provide any additional conveyance capacity that might be required should the storm hit. The new segment of the force main was quickly connected to the rest of the system, delaying completion of the pressure test.
A storm did in fact develop over Oahu, and the system performed as required. The following week, the required pressure test was completed. The line was then reconnected and the project was completed. This first pressure pipe lining project on the island is considered a success, and it has provided a newly rehabilitated pipe over the course of several days with minimal impact to the busy roadway.