Empirical geophysical/geotechnical relationships in the Champlain Sea sediments of eastern Ontario

Abstract

Geophysical and geotechnical data are presented from different sites in eastern Ontario where variable geotechnical properties of Champlain Sea sediments (‘Leda Clays’) are found. Sites range from thick “undisturbed” silts and clays, to “disturbed” geologically similar soils (earthquake triggered landslides and other deformed materials). High-resolution seismic profiles provide stratigraphic context for some of the boreholes drilled in the study area. Downhole geophysical logs from 14 boreholes are compared to core sample measurements of porosity, sensitivity, and porewater conductivity to develop useful empirical relationships. According to these relationships, silt and clay sediments can be sensitive or quick when formation conductivity drops below 100 mS/m. Conversely, silts and clays with elevated conductivities (>250 mS/m) are rarely sensitive. Salinity values calculated from porewater conductivity indicate sensitive or quick behaviour may be expected in leached soils when salinity drops below 2 g/l.