Quasi-overconsolidation and creep phenomena in shallow marine and estuarine organo-calcareous silts, Fiji

Abstract

Nearshore, estuarine deposits of Holocene organo-calcareous silt provide the most common setting for foundation failure in Fiji. Creep is implicated in long-term settlement. Although the geological history indicates the deposits should be normally consolidated throughout, there is increasing apparent overconsolidation towards the surface. This finding is contrary to what might be expected if delayed compression alone was operating. The phenomenon appears to be related instead to organic content and may be affected by strain rates during consolidation. Oedometer tests extending over 7 months indicate the rate of volume change due to creep follows the Singh–Mitchell relationship, but calculation of secondary compression from radiocarbon dates suggests that the very long-term rate is higher than might be expected. Creep appears to be stress dependent, at least below the preconsolidation pressure, in common with other marine sediments. Key words : silt, organic, preconsolidation pressure, overconsolidation ratio, secondary compression, creep, radiocarbon dating.