Tunnel Leak Remediation at the Toronto Subway

The spring of 1997 marked the beginning of a professionally engineered, state-of-the-art remediation grouting program at the Toronto Transit Commission (TTC). A Tunnel Leak Remediation program was developed with the objective of stopping the water infiltration problems that plagued the Toronto subway tunnels since their construction. Water infiltration into the subway tunnels results in service affecting delays as well as concerns relating to the safe operation of a transportation system serving over a million riders per day. Problems include: accelerated aging of the rail and rail fastening systems, deterioration and malfunction of electrical systems and associated components and deterioration of the structure itself. A two-hour nightly working window, in which maintenance activities can be performed, combined with the marginally injectable ground conditions and difficult tunnel structure made achieving positive results especially challenging. An engineered solution grouting injection program using acrylamide technically proved to be the most suitable design for this particular application. The newly hired in-house work force had never previously worked with acrylamide solution grouts and therefore had to be trained and coached in all aspects of the grouting procedures. The acrylamide grouting operation is closely monitored under stringent quality control parameters and is implemented under what is likely one of the highest levels of personal protection ever used for an acrylamide grouting application. Acrylamide was never previously used anywhere on Toronto Transit Commission property, but it has demonstrated to be an invaluable tool in solving difficult water infiltration problems in difficult ground conditions under a limited two hour working window. This paper shares some of the experiences gained to date in this on-going Tunnel Leak Remediation Program at the Toronto Transit Commission.