Bi-Directional Static Load Test for Caissons in Georgian Bay Shale: A Case Study in Greater Toronto Area, Ontario

ABSTRACT: Rock-socketed drilled shaft foundations for Ministry of Transportation Ontario (MTO) projects have traditionally involved relatively long sockets relying on a significant proportion of sidewall resistance, which may not take full advantage of base resistance. A shorter, more efficient rock socket was designed for bridge piers in weak to medium strong Georgian Bay shale as part of the twinning of QEW/Credit River bridge in Mississauga, Ontario. An axial bi-directional static load test, also called an Osterberg cell or “O-cell” test, was completed to measure the ultimate sidewall and base geotechnical resistances of the rock socket on the test shaft, for comparison to and verification of the factored geotechnical resistance used in the design of the production drilled shafts. These results expand the knowledge base for caisson foundation design in the Georgian Bay rock formation, and demonstrate the effectiveness of SQUID, CSL and TIP in interpreting O-cell test results and in quality control during construction.