City of Toronto Water Main Rehabilitation Between Island Water and John Street Station

Rehabilitation, Water Transmission

Toronto Water Slipline Tunnel with Engineered Steel Pipe

Pipe Specifications:

2,669 feet of 84-inch ID x 1-inch wall engineered spiralweld steel pipe with bare coat and cement mortar lining; bell-and-spigot lapweld joints



Engineer Firm:

R.V. Anderson Associates Limited


McNally International Inc.


Toronto Water

This project’s purpose is to rehabilitate a century-old water transmission tunnel that runs below Lake Ontario. The tunnel is between the Island Water Treatment Plant and John Street Pumping Station, which is the largest Water Pumping Station in the City. The horseshoe-shaped tunnel arch was originally built with brick and cement mortar and required rehabilitation due to the tunnel top reacting to seismic stress. To prevent structural failure of the tunnel, Toronto Water opted to reline the existing tunnel with engineered steel pipe. Using a sliplining method, the installation contractor McNally International inserted 20-foot segments of cement mortar-lined one-inch-thick steel pipes into the tunnel and connected each adjoining pipe with an internal lap weld on the bell-and-spigot joints.

The annular space between the host pipe and the slipliner sections was filled with cement mortar grout to passivate the steel pipe. A cement mortar lining (AWWA C205) was installed at our plant and provides internal corrosion protection. The design team employed the sliplining method because the 84-inch diameter pipe provided the necessary waterway opening at a lower cost compared to other relining methods.

To place each piece of pipe, the contractor built a rail track system through the existing tunnel and carried each piece of pipe to its final destination. The manufacturing team at our Parkersburg plant opted to use a 36,000 yield steel compared to the typical 40,000 yield steel to accommodate forming the one-inch material.

Frequent teaming partner McNally International completed the installation in the fourth quarter of 2021 with ease. Armenio Martins, Project Manager at McNally stated:

“The job went very well. Northwest Pipe manufactured quality pipe that was delivered within a very small window of time. Installation went according to plan with no issues.”