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After complete failure of a 102-inch (2600 mm) diameter
water line section, the Providence Water Supply Board
took action to prevent future blowouts. The possibility
that other sections of the 50 year old precast concrete
pipe could rupture prompted a condition evaluation
and strengthening program. Inspection revealed vulnerability
in 11 nonconsecutive, 16-foot-long (5 m) sections
within five miles of pipeline.
A carbon fiber in-situ lining was determined to be the fastest, least disruptive, and most cost-effective solution. Multiple layers were wrapped around the circumference of the pipe as well as in the longitudinal direction. A waterstop termination detail was designed for the end of each section to eliminate the chance of water getting behind the FRP system. A full-scale test proved the integrity of the system and assured the owner that strength would be added to the pipe sections.
The strengthened pipe sections were buried 15 to 20 ft (4-1/2
to 6 m) underground and some were miles apart. Some service
holes were spaced 2000 ft (610 m) apart. The confined space
environment required special safety measures including air
monitors and a ventilation system. Blowers, dehumidifiers,
and heaters kept the relative humidity and temperature at ambient
levels.
This aqueduct system was the first in the world to install an in-situ FRP sheet in potable water pipes for strengthening. This is a model project for other water utilities in similar situations where excavation of pipes is not cost-effective or desirable. By using the FRP method, Providence Water did not have to dig, replace, or line long segments. Along with thorough planning, the lightweight, flexible carbon fiber helped overcome the challenging working conditions and provided a fast, effective solution.
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