The Lachenaie clay deposit: some geochemical and geotechnical properties in relation to the salt-leaching process

Abstract

This paper summarizes a detailed geotechnical and geochemical characterization program for the Champlain clay deposit in Lachenaie, Quebec. Presently, the clay pore water is saline. The main objective of the testing program was to study the leaching of the clay saline pore water since its deposition. Four issues are discussed in this paper. First, the deposit is shown to comprise two distinct clay layers with contrasting geotechnical properties. The liquid limit and grain-size distribution are the properties that best distinguish the two materials. The upper layer is more plastic while the lower one is relatively silty. The occurrence of these two layers is shown to be in agreement with some recent findings in Quaternary geology. Second, the relatively high pre-consolidation pressures of the clay in the Lachenaie area are shown to be coherent with an erosion scenario and the elevation of a neighbouring bluff previously interpreted as an erosion terrace. Third, the relatively constant hydraulic conductivity values obtained from permeability tests throughout the deposit are shown to be consistent with the variations of liquid limit and void ratio in the two clay sublayers. Fourth, the occurrence of sensitive clay pockets (sensitivity greater than 50) in this otherwise saline clay body is elucidated.