Toronto's Tunnel Solution (Available in the Geoenvironmental Special Section only)

by Luigi Narduzzo, P.E., Leak Remediation Engr.; Toronto Transit Commission,

Serial Information: Civil Engineering—ASCE, 2000, Vol. 70, Issue 10, Pg. A10-A16

Document Type: Feature article


The Toronto Transit Commission (TTC), one of the largest public transportation systems in North America, carries more than 1,000,000 commuters a day. The TTC's tunnels had not received a major restoration of any kind since their construction, but over the years, water infiltration into the tunnels had contributed to delays and safety concerns. The leakage also contributed to a large range of problems, such as extensive concrete and steel deterioration, an accelerated life cycle for the rail and rail fastening systems, deterioration and malfunction of electrical systems and their components, and decay of the structure itself. In view of the great need for structural maintenance, the TCC made tunnel leak remediation a primary objective. The engineers decided that a state-of-the-art acrylamide grouting program would bring an end to the water infiltration problems. Acrylamide was chosen because of its controllable set times, its ability to penetrate the finest and tightest fissures and low-permeability soils, its ability to absorb surrounding water and encapsulate it in the final gel, and its low initial viscosity. The engineers also found that they could accurately predict the volumes of the acrylamide to be used at each location, allowing a precise quantity of material that can be batched on a given shift. The results attained to date have been very successful, and the program is expected to expand in the years to come to include a second grouting work car and a larger crew.

Subject Headings: Tunnels | Electrical systems | Steel structures | Rail transportation | Public transportation | Infiltration | Grouting | Toronto | Ontario | Canada

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