The Northwest Suburban Municipal Joint Action Water Agency maintained service to half a million people while almost seven miles of 90-inch transmission main were being relocated to accommodate tollway widening. The thrust-restraining system that kept 1.3 million pounds of force during hot tapping from causing catastrophic joint failure earned an engineering award in February 2017. The project’s location near a creek made controlling groundwater infiltration an additional challenge.
Bar-wrapped, steel-cylinder, reinforced concrete pressure pipe lengths are joined with steel spigot rings fitted with rubber gaskets and grouted to seal the connection. Engineers determined that displacement of more than 1/16 an inch could cause the joints, which were under 165 psi, to fail.
To transfer bulkhead forces into the ground and stabilize the tapping location, they devised a shock-absorbing “cradle” consisting of concrete-encased caissons placed on either side of the pipe. The cradle segments are made from a special concrete mix and a combination of mechanical and chemical bonds was developed with the outer mortar coat.
Crews work to set the Stopple Stopple housing and connect to the bypass line after the 60-inch tapping hole was cut into the existing line.