A Till Cofferdam in the St. Lawrence River

This paper deals with the design, construction, and performance of a drydock in the St. Lawrence River enclosed by a till dyke dumped in water. Alternative designs and methods of selecting a suitable till are discussed. Construction procedures are described along with the installation of a two-stage wellpoint system to intercept seepage through the riverbed beneath the dyke. Particular emphasis is placed upon the methods of control and observations taken both during and after construction.It is concluded that a till dyke dumped in water can form as table and impermeable mass; however, care must be taken to apply any surcharge slowly to allow time for the dissipation of pore pressures in the underwater till.