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 (led by SNC-Lavalin) for the design and construction of the Réseau express metropolitain (REM) in Montreal which will be one of the largest automated transportation system in the world. Out of the 67 km network, over 25 will be constructed on 650-span elevated structure founded on large diameter single drilled shaft socketed into rock. In order to optimize the JV team performed two full-scale, bidirectional (Osterberg Cell) static load test in the two rock formations encountered along the alignment and two fully-instrumented lateral load tests in critical areas along the alignment, one in the cohesive soil of the Champlain Sea clay and the other in cohesionless soil.
In addition to a brief description of the construction procedure of the load test shaft, this paper presents design details on the back-calculated side and base resistance values, a discussion on the displacement incompatibility of skin friction and end bearing, and a procedure to estimate a site-specific design value for the load transmitted to the tip. A simple method to estimate the ultimate shaft resistance in locations where the rock is of different quality than the rock at the load test location is discussed. As for the lateral load test, this paper presents a comparison of the lateral load test results with the lateral shaft response as simulated by LPile software, using _p-y_ curve of API sand and Reese models for cohesionless soil; and API soft clay for the cohesive soil. The _p-y_ curve as obtained from the pressuremeter tests performed in both cohesive and cohesionless soils are also compared to the lateral load test. The calibration of the design models to the load test led to reliable foundation performance with shorter shaft, helping to reduce cost and mitigate construction issues associated with unnecessarily long shafts.
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