Geotechnical, Geophysical and Hydrogeological Characterization of Soft Sensitive Leda Clay in Ottawa and Associated Challenges in Foundation Seismic Design

ABSTRACT: A geotechnical, geophysical and hydrogeological investigation was conducted in Champlain Sea basin to 30.5 m depth for the design of a new control building with basement and a deep metering chamber extending to about 12.4 m depths at the existing Delorme wastewater pumping station in Ottawa. The Site is about 4 km south of Ottawa River within the major physiographic region of the Ottawa - St. Lawrence Lowland and the minor physiographic region known as the Ottawa Valley Clay Plain. The investigation found thick deposits of sensitive Leda Clay and mostly non-swelling marine clay, silty clay and silt deposits extending beyond 30 m depth. Considering the high sensitivity and weakness of this Leda Clay with moisture contents wet of Liquid Limit and observed groundwater below the upper crust and the resultant seismic site classification and anticipated loading, this case study discusses both the design and potential constructability issues and challenges.