Various kinds of cyclic shear tests on sand under drained and underained conditions were performed to investigate stress-strain behavior (particularly soil dilatancy) under cyclic loading due to earthquake, ocean wave and others. Not only conventional triaxal tests but also true triaxial test in which three-principal stresses can be controlled independently were carried out. The stresses change their directions arbitrarily in the ground during earthquake or ocean wave loading. It is then important to investigate the stress-strain behavior including soil dilatancy in general stress condition. It is experimentally shown that the dilatancy characteristics of sand depends not only on the amplitude but also on the initial stress ratio and the direction of principal stresses.
Many elastoplastic models for sand under cyclic loading have been proposed (e.g. Hashiguchi,1980; Oka and Washizu, 1981; Nakai, Fujii and Taki,1989), and many cyclic shear tests have been performed to investigate experimentally the cyclic shear behavior, of sand and/or verify these models (e.g. Ishihara, Tatsuoka and Yasuda,1975; Wood,1982). The applicability of these models were confLrmed within a limited stress conditions such as cyclic triaxial tests with equal amplitude after isotropic consolidation. However, it is necessary to check the validity of the models m general stress conditions with various amplitude to apply them to the analysis of practical dynamic problems of soil ground (e.g. liquefaction analysis). For this purpose, the authors performed several kinds of drained and undrained cyclic tests with different amplitudes and different shear stress histories, using conventional triaxial test apparatus and true triaxial test apparatus.
To investigate stress-strain behavior of sand under cyclic loading, triaxial tests and true triaxial test on medium dense Toyoura sand (mean diameter D50=0.2mm, uniformity coefficient Uc=l.3, specific gravity Gs=2.65, relative density Dr=73%) were performed in drained and undrained conditions.