Geotechnical Challenges Associated with the Design of the REM Project in Montreal

In 2018, the Caisse de Dépôt et Placement du Québec (CDPQ) awarded a $6.3 billion design-build contract to the Joint Venture (JV) team NouvLR for the design and construction of a 67-km light rail system called the REM in Montreal, which will be one of the largest automated transportation systems in the world. The complexity of the project posed unique geotechnical challenges on many levels. Part of the alignment was constructed over peatland where low bearing capacity and excessive settlement obstacles needed to be overcome. Many small and large diameter utilities, running in the vicinity of proposed embankments, required the design of a protection system by mean of column supported embankment. Part of the alignment was to be constructed over an old landfill where the subsurface investigation indicated up to 9 m of solid waste. Presence of over 10 m of soft to firm silty clay required ground improvement using semi-rigid inclusions (such as Controlled Modulus Columns) to minimize settlement. Numerous segments along the project alignment were found to be underlain by potentially liquefiable soils where laboratory cyclic direct simple shear (DSS) tests were performed to assess liquefaction potential. Furthermore, over 25 km were constructed on 650-span elevated structure founded on single drilled shafts socketed into rock. To optimize the shaft design, three full-scale, bidirectional (Osterberg Cell) static load tests and two fully instrumented lateral load tests in critical areas were performed. The paper discusses the static load tests results as well as the different issues and concerns raised during the geotechnical design and how these were addressed.