Undrained Deformation and Strength Characteristics of Soils from Reclaimed Deposits in Kobe

Abstract

The reclaimed lands in port and harbour area of Kobe city developed extensive liquefaction during the intensive shaking of the 1995 Hyogoken-Nambu earthquake. Among these islands, the northern portion of Port Island was reclaimed with soil materials consisting of decomposed granite. Masado, a soil containing about 50% gravel had been considered to be less liquefiable than clean sand. This catastrophic event, however, created the need to re-examine the susceptibility of such gravelly soils to liquefaction. To examine the undrained behaviour of the Masado soil, a multiple series of triaxial compression and extension tests was carried out on reconstituted soil samples as well as on intact soil samples. Two different preparation methods were employed to produce samples with different fabrics. The different soil fabrics prepared by the different methods were shown to exhibit different undrained deformation behaviour during monotonic straining. However, the largely deformed steady states of specimens having the same grain size characteristics were shown to be determined uniquely independent of the method of sample preparation, and also whether the deformation mode is triaxial compression or extension. It was also found that the steady state lines for soils of decomposed granite with different particle gradations are parallel to each other in the plot of void ratio against logarithm of effective confining stress. The steady state characteristics of the Masado soil based on the laboratory tests are described in this paper.