The end of the sinkhole saga on Winnipeg Street is in sight as contracted crews and workers with the City of Prince George prepare to install a 9.0 metre by 4.8 metre concrete chamber to replace a failed section of sewer pipe, which has caused several sinkholes at that location over the past few years. For the past two weeks, crews have been constructing the chamber on-site and allowing the concrete to cure to a strength that will allow it to be lifted by a crane during installation and to withstand the pressure of large storm events like the one in June that preceded the most recent sinkhole at that location.
Following an extensive operation to remove groundwater from around the sewer pipe that involved installing dams and three high capacity pumps to drain water from the site, it was discovered that over eight metres of pipe is completely deteriorated at the sinkhole. The City believes the deterioration was caused by turbulence from the discharge of storm water from the Carney Street storm sewer that enters the pipe at the location of the failed pipe.
“The pre-cast concrete chamber is designed by engineers to withstand the turbulent forces of large amounts of water flowing through it during storm events,” says Josh Kelly, Supervisor of Energy, Environment, and Sustainability. “Now that the chamber has set to the required strength, a crane is being used to install each of the four 23,000 kilogram sections to replace the deteriorated portion of the metal pipe.”
Following the installation of the chamber, the watermain at the site will need to be replaced, traffic signal streetlight poles must be reinstated, and backfilling will proceed to restore the road base. Depending upon the weather, the City estimates the entire intersection will be repaved and reopened to traffic by mid to late October.