Liquefaction Behaviour of Osaka-group Coarse Sandy Soils

An investigation of the shear behaviour of Osaka-group coarse sandy soils by employment of the undrained speed-controlled ring shear test and the undrained strain-controlled triaxial compression test was conducted. A wide range of initial states of sand are covered to investigate a full spectrum of the shear behaviour including liquefaction and the newly proposed sliding-surface liquefaction. A comparative analysis by both soil tests suggests the followings ; (1) as to loose specimen at almost same relative density, the different types of liquefaction were generated (the triaxial compression test yielded conventional liquefaction and the ring shear test generated the sliding-surface liquefaction), (2) a clear shear plane appeared in the dense specimen for the triaxial compression test played an important role in excess pore pressure generation due to grain crushing.Next, the stress condition which marks the onset of collapse and the consequence of liquefaction after long shearing were examined using the ring shear test. It was revealed that the collapse behaviour took place in effective stress path reaching a certain stress ratio for normally consolidated specimens by the undrained ring shear test. And the steady state line from the ring shear tests which is obtained after the termination of grain crushing is located below that from the triaxial compression tests. It is interpreted as an ultimately obtained steady state, and it is called “ultimate steady state line.”