Physical, chemical and mineralogical influences on the rheology of remoulded low-activity sensitive marine clay

The rheological response of remoulded Leda clay from the South Nation River landslide (1971) site has been investigated using a coaxial viscometer. The yield stress at constant water content was found to: decrease as the pore-water salinity decreased, with the decrease occurring at much lower salinity when Ca-saturated than when Na-saturated; decrease as the clay content of the soil was decreased; decrease upon the extraction of oxide minerals by dithionite–citrate–bicarbonate; decrease when the phyllosilicate content of the soil was depleted by a severe alternating acid/base extraction procedure; increase as the pH of the marine clay, whether carbonate-containing or carbonate-free, was lowered by acid addition. The effects are in agreement with expectations based on electrical double-layer theory. The relative effects of the various pretreatments are qualitatively discussed. Viscoplastic-shear-thinning and Bingham plastic response most commonly occurred, although at low salinities viscoplastic-shear-thickening response was exhibited for materials with high silt contents and after phyllosilicate-depletion. No relationship between flow type and the tendency to exhibiting quick clay behaviour is apparent.