Abstract
A traffic causeway placed on the sediments of saline Tramping Lake failed during construction in the summer of 1982. Vertical subsidence has continued until present (1988). The failure mechanism was controlled by sedimentary structure and artesian groundwater conditions. The shear zone is in a soft, near normally consolidated lacustrine sandy silt unit 22 m thick. The lake basin contains lacustrine, deltaic, and fluvial deposits of postglacial origin. Artesian conditions in the Upper Cretaceous Judith River Formation and postglacial fluvial sand and gravel dominate the hydrogeology at the site. The failure took place along a composite slip surface when excess pore-water pressures developed during loading [Formula: see text]. The estimated effective friction angle from triaxial tests and back calculation was 27° assuming c′ = 0. However, a parametric analysis showed that at very high pore-water pressures the effective friction angle required for equilibrium is very sensitive to small variations in ru. The calculated cohesion at [Formula: see text] required for equilibrium was 3.9 kPa, whereas the remolded vane strength measured in the field was 5.0 kPa. Key words: Foundation failure, artesian, saline environment, groundwater discharge, silty clays, postglacial fluvial and lacustrine deposits.
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