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1 Groupe de Géologie de l'lngénieur, Département de Géologie, Université Laval, St-Foy, P.Q., Canada, G1K 7P4;
2 Département de Génie Civil, Université de Sherbrooke, P.Q., Canada, J1K 2R1
Sediments of the Grande-Baleine River were deposited in a brackish sea about 7000 years ago; the salinity was not less than 8 g/1. This fine-grained sediment was uplifted more than 150 m above sea level. The soil is extremely sensitive (St > 200 as measured by the fall cone), the liquidity index is often above 2. In the odeometer, this sediment is highly compressible and presents an overconsolidation ratio greater than 2 and this with signs of little erosion. Research work has yielded a behavioural model that includes different processes such as early cementation during or soon after deposition and leaching to the actual porewater salinity of 0.5 g/1. Both processes have resulted in a sediment with abnormally high water content (with respect to effective stress) and a high liquidity index, due in part to leaching. Field and laboratory work demonstrate that for this soil, processes responsible for its structuration are leaching and cementation (or anything that has prevented the soil from consolidating completely). No evidence could be found that would suggest the action of delayed consolidation. Today this soil appears geologically normally consolidated (i.e. there is no erosion or surcharge), mechanically overconsolidated (O.C.R. >2), and physico-chemically underconsolidated (abnormally high water content).
