Proposal of a Simple Method for Assessing the Susceptibility of Naturally Deposited Clay Grounds to Large Long-Term Settlement due to Embankment Loading

A simple method that utilizes the results of laboratory tests has been proposed for determining the susceptibility of soft clay grounds to large residual consolidation settlement due to embankment loading. It was found that there is a possibility of large long-term settlement if the sensitivity and compression index ratios of the clay material that constitutes the ground are equal to or more than 8.0 and 1.5, respectively. The compression index ratio is defined in this paper as the ratio (Cc/Ccr) of the steepest gradient of the compression curve of an undisturbed sample to that of the remolded sample. Through the SYS Cam-clay model, an elasto-plastic constitutive model that describes the actions of the soil skeleton structure, it was found that clays with large sensitivity and compression index ratios are characterized by initially highly structured soils and that decay/upgradation of the structure can easily occur due to plastic deformation. In addition, by following Schmertmann's graphic method for in-situ compression curve (1953), this paper proposes a method of deducing the in-situ initial conditions from the results of laboratory consolidation tests on undisturbed samples. These investigations revealed not only that large delayed settlement is facilitated in clays, which have higher degrees of structure and faster rates of structural decay, but also that the Δe method and other simple methods of predicting settlement may underestimate the amount of settlement.