Abstract:
The City of Toronto is in the midst of reshaping and revitalizing its waterfront - the largest urban redevelopment project in North America. One aspect of the redevelopment includes naturalizing the mouth of the Don River, which has been become a source of flooding as a result of decades of infilling and heavy industry. Constructing a new river mouth involves multi-staged excavations up to 6 meters below Lake Ontario in permeable alluvial sands. In order to place a protective environmental barrier, these excavations need to be dewatered and require cantilevered earth retention of over 6 meters in height.
This presentation will focus on a 1.1-kilometer-long, 1.2-meter-wide, 45-meter-deep secant pile cutoff wall that was constructed to support the excavation and dewatering of the river mouth. The wall was designed to provide hydraulic cutoff and retain up to 6.8 meters of soil and water. The presentation will discuss (i) design of the cutoff wall and determining embedment into bedrock, (ii) verticality criteria and challenges associated with a deep secant pile cutoff wall, (iii) results and trends of verticality measurements from 850 piles, (iv) performance of the cutoff wall and comparisons to design predications, and (v) challenges experienced during construction.