Two case histories on long-term settlements of Ariake clay which is counted as one of the soft clays in Japan are described. The one of them is to report the settlement which have been observed over 25 years since construction of embankment for breakwater on the coastal Ariake deposit. The another case history is concerned with the settlement of low embankment highway on Ariake clay whose shallow surface was improved by quickline-clay mixture as a countermeasure for the settlement. The current paper is featured by the fact that the predominant secondary settlement is common with two case histories. The finite element method using an elasto-plastic mo1el was adopted to analyze the settlement of the Ariake clay observed in the above-mentioned two case histories under sustained and transient loading, respectively. It is concluded from comparison of analytical results with observed settlement that the proposed model with consideration of secondary compression is advantageous for long-term settlement prediction of soft clay
