The determination of the undrained strength of n-situ soft marine clays is studied. The content of this study is summarized as follows:
1)There were remarkable differences in the average of qu(unconfined compression strength) among the companies. In a case of X port, the reported qu of a company was 30% smaller than that of another company. These differences were due to the degree of the sample disturbance, namely the sampling techniques.
2)There exists two types of sample disturbance making great effects on qu. One is the remolding type disturdance, and the other is the crack type disturbance. It was found that, in some cases, the crack type disturbance were major cause of the scatter of qu.
3)By consolidating clay slurry at high temperature (75C°), were produced reconstituted clays whose strength-deformation characteristics simulated natural aged clays.
4)A new practical method for determination of the undrained strength of clayey ground was proposed. In this method, 3 unconfined compression tests and one Simple CU Test are carried out with each thin wall tube sample. By comparing the half of the mean unconfined strength qu/2 to the strength of the simple CU test, the quality of the sample and the strength to be used as design parameter are determined.
5)Using the new method proposed in this study, the qualities of the undisturbed samples taken from 50-400m depth were mostly estimated as large disturbance.