Project Generates Pipe Performance Data After Rehab
The region of Ottawa-Carleton, which provides water for 11 municipalities including Ottawa, has successfully rehabilitated one of its feeder mains in downtown Ottawa, using the sliplining technique. The old 915-mm (36-inch) ID cast iron water main was originally constructed between 1916 and 1917. Its operating pressures range from 275 to 690 kPa (40 to 100 psi), with additional transient pressures up to 345 kPa (50 psi). Before the rehabilitation, two ruptures had occurred on this feeder main, which is 1,500 m (4,920 feet) long.
An 840 mm (33-inch) O.D. DR 17 HDPE pipe was chosen to slipline the 82-year-old cast iron pipe. The annular space between the HDPE and host pipe was grouted. To study the performance of the water main after rehabilitation, a monitoring scheme was designed and implemented during the field installation.
This monitoring system consisted of eight pairs of strain gauges on the internal surface of the cast iron pipe and 16 pairs of strain gauges on the outside of the HDPE pipe. These gauges were installed at two locations without excavation.
After the strain gauge installations, the HDPE pipe sections with the sensors were butt-fused to regular HDPE lengths. To minimize damage during the insertion process, the cables from the sensors on the cast-iron pipe were anchored snugly on the inside of the cast-iron pipe and those on the HDPE pipe were taped snugly to the outside of the HDPE pipe. Preliminary data indicated 75 percent of the sensors survived the harsh installation process.
In addition to the strain gauges, arrays of thermocouples were installed in the backfills above the pipe. Two time domain reflectometry probes were installed in the backfill soils to measure the in-situ moisture contents. A pressure transducer was installed to measure the hydrostatic pressure inside the water main. All the installed sensors were controlled by two on-site dataloggers in a buried valve chamber. Remote communication with the monitoring system was done via a modem.
The main will be monitored for five years starting in July 1999 when the main became functional again. The first four months of data show that the system is working properly. It is providing useful data on internal operating pressures, changes in temperature of the conveyed water, frost penetration rates in the backfill and in-situ moisture contents.
After the five-year monitoring period, the data will help verify the predicted performance of the sliplined water main under various load combinations including frost loading.
Collaboration between Michael Willmets, Michel Robitaille, Daryl Upton of the region of Ottawa-Carleton, Derek Potvin of Robinson Consultants Inc., Dufferin Construction Co. Ltd. (the contractor) and the NRC research team made the implementation of the performance monitoring system a success.
About the Authors:
Lyne Daigle is a Technical Officer with the Urban Infrastructure Rehabilitation Program at the Institute for Research in Construction, National Research Council Canada. Richard Desnoyers is a Technical Officer with the UIRP at the Institute for Research in Construction, NRC Canada. Jack Zhao is a Research Officer with the UIRP at the Institute for Research in Construction, NRC Canada.