Back-Wall Grouting using Acrylamide Successfully used in Toronto's Subway

Plagued by leakage problems since the time they were constructed, Toronto's underground network of subway tunnels and structures have undergone a major leak remediation program. The spring of 2004 marks the seventh year of a very successfully implemented solution grouting program. This project has been the largest on-going solution grouting project in North America for the last five years. The Toronto Transit Commission's water problems were brought under control with the use of a "back-wall" grouting technique that took into account the multiple phase, multiple stage grouting operations that were anticipated and required to successfully shut off the leakage problems. The water infiltration problems was causing accelerated aging of the rail and rail fastening systems, deterioration and malfunction of electrical systems and their components and decay of the structure itself as well as causing both service delays and concerns for passenger safety. All the work had to be performed during the nightly two-hour maintenance working window without impact to customer service. This paper hopes to provide some helpful insight on the key aspects of this specific sealing system engineered and designed to solve Toronto's subway tunnel and station leakage problems. This successful design continues to be the leak remediation solution of choice for this public transportation authority.