The strata of sea off Sensyu in Osaka Bay consist of very soft alluvial clay and diluvial clays which continue more than 400 meters. There is a big project to reclaim land from the sea to construct New Kansai International Airport in this area. It is predicted that the reclamation and the construction of airport facilities will give so much stress increments as to exceed the preconsolidation stress not only to the alluvial stratum but also to the deep diluvial strata. Therefore, it is necessary to investigate soil properties of these clays.
　A series of triaxial compression tests and triaxial creep tests are carried out with undisturbed soil samples. The following conclusions can be drawn from the present study.
　1) There is not a unique relationship between strength parameters of diluvial clays and plasticity index.
　2) The rate of increase in undrained shear strength of deep diluvial clays is smaller than that of alluvial clays.
　3) The time effect of underained shear strength in Sensyu alluvial clay is as much as that of Daikoku clay in Tokyo Bay.