Managing subsurface risk for Toronto's Rapid Transit Expansion Program

The design and construction strategy adopted to manage subsurface risks on Toronto’s Rapid Transit Expansion Program are described. Measures include a “risk sharing” approach to construction contracts, a commitment to comprehensive pre-construction site investigation and appointment of a Program Geotechnical Consultant. The role of the Program Geotechnical Consultant in planning investigations, ensuring consistency in quality and providing a consistent interpretation of subsurface data is described. The level of site investigation effort for the major tunnelling contracts is related to construction risks, such as change orders, to assess the optimum level of investigative effort. The “risk sharing” approach to construction requires preparation of a Geotechnical Baseline Report and the appointment of a Disputes Review Board for each major civil works contract. The approach to providing “baseline” conditions for typically contentious issues, like boulder frequency, is described.