Toronto-York Spadina subway extension tunnelling under Schulich Building

Abstract

Tunnelling under the York University Schulich Building was one of the milestones of the Toronto-York Spadina Subway Extension Project. The challenge was to bore the tunnel under a flagship building only one diameter below the foundation without a compensation grouting process. Intensive finite element structural and geotechnical analyses of the building and the tunnel were performed, together with monitoring field measurements. The results showed that compensation, included in the initial design, was not necessary to ensure the building’s structural integrity. The tunnel monitoring during crossing confirmed the results of the performed analyses. The paper highlights the difficulty of deciding whether a compensation grouting is necessary or not when tunnelling under buildings and explains the procedure that was followed in this particular case.