EFFECTS OF THE STIFFNESS OF SOFT CLAY LAYER ON STRONG MOTION RESPONSE

AKIRA YAMAGUCHI, MOTOKI KAZAMA, HIROFUMI TOYOTA,
MASAKI KITAZUME and TAKAHIRO SUGANO

ABSTRACT: This paper shows the effects of the stiffness of underlying soft clay layer on the strong motion response. Seismic behavior of the Kobe artificial islands during the 1995 Hyogo-ken Nambu earthquake is studied by using centrifuge shaking table test. At the earthquake, it is known that the liquefaction damage of artificial island was different from each site. Authors consider the reason why is due to the stiffness of clay layer underlying the reclaimed ground due to the degree of consolidation. The model grounds used for the centrifuge test are made by the clay and fill material sampled from Kobe Port Island, and the clay material is consolidated as two different degree of consolidation, which correspond to those of Port Island array observation site and south-western part of Rokko Island. First, from the viewpoint of the reproducibility of in-situ behavior, we compared the seismic response and the ground settlement obtained from centrifuge test with those of the observation data of Port Island. Next, we compare the seismic response of the test results of the different degree of consolidation. It is found that the difference of stiffness due to the degree of consolidation of the underlying clay layer significantly affects the seismic behavior of reclaimed ground. The large damage is not always come to being on the ground with soft clay layer.

Keywords: Holocene clay, the degree of consolidation, (centrifuge shaking table test), decomposed granite soil, liquefaction, stress-strain curve (IGC: D7/E8)