At Dundas St West and the Annette St and Dupont St. crossover and along Hook Ave for a short Junction railroad history is being made. Right now contractors are forcing into the ground retaining walls to form the walls of the underground corridor which will carry the Canadian National (CN) tracks under the Candaian Pacfic Railway tracks (CPR).
Information on the process from one of the engineering companies involved
The retaining walls comprising the depressed corridor are approximately one kilometer in length, with a maximum excavation depth of 11 metres. A very significant added complication to the project was the relatively shallow ground water table which was found approximately five metres below existing grade.
The proposed wall system set out in the preliminary design report for this project was an interlocking steel pipe piling system. This type of piling was developed in Japan and was found to be virtually unknown in Ontario. It proved to have a number of advantages including the potential to virtually eliminate de-watering from this project, by means of cutting-off the ground water by means of the permanent steel pile walls. Extensive de-watering would otherwise be required and it was anticipated that such de-watering would be costly, subject to risks, claims
and delays, and the subject of concerns from environmental perspectives as long-term dewatering could draw contaminants to the site.
Here is a link with hoards of technical information and some great images – a PDF will open in a new window