It has been well indicated that the effect of soil structure should be taken into account to interpret mechanical behavior for most naturally sedirnented soils. For assessing the effect of soil structure on mechanical behavior, it is important to understand the sedimentation state of natural sedimentary soils. Skempton has presented the so-called sedimentation compression curves with relating void ratio to effective overburden pressure based on extensive data of normally-consolidated deposits, strata that have never been under a pressure greater than that the existing effective overburden load. Based on the data published by Skempton, Burland has proposed a so-called sedimentation compression line (SCL) with introducing a so-called void index Io. Sensitive days, however, are excluded from their studies. In this study, the extensive data on the typical sensitive clays in Japan, Ariake clays, are used to investigate the sedimentation state in comparing with the SCL. It is found that the natural Ariake clays with liquid limit being larger than 120% lie around the SCL, but those with liquid limit less than 120% lie above the SCL For a given value of effective overburden pressure, the Io with lower liquid limit lies above that with higher liquid limit. The leaching of salt occurred at Ariake clays is considered to be the most important factor for such a phenomenon. Leaching of salt decreases the liquid limit, consequently increasing the normalized water content w* defined as the ratio of natural water content over liquid limit. The analysis also indicates that the value of Io increases linearly with the increase in w*. Hence, leaching of salt increases the value of Io thus causing the data of Io lying above the SCL.
It is well known that for most naturally deposited soils the soil structure develops during the depositional and the post-depositional processes (e.g., Bjerrum, 1967; Schmertmann, 1991; Hong and Tsuchida, 1999).
