A site in Châteauguay, south of Montréal, Québec, Canada, was investigated as part of the design of a significant infrastructure project. A loose marine silt layer present at the site was found to be susceptible to liquefaction using conventional empirical techniques based on CPT, SPT and classification data.
To mitigate this hazard, a program of careful undisturbed sampling and advanced laboratory testing, including cyclic direct simple shear testing, was undertaken to investigate in detail the properties and cyclic behaviour of the soil. The magnitude of cyclic loading was determined from the site-specific seismic hazard assessment and site response analyses. Post-cyclic testing of the static strength of the soils was undertaken to establish the residual strength of the soils. The laboratory results confirmed that the silts would soften under this cyclic loading but that they would not liquefy. The use of conventional liquefaction assessment techniques was found to be conservative in these soils.