Study on the evaluation of the mechanical properties of sandy grounds and their test methods

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The following conclusions can be drawn based on the co-operative research on the mechanical behavior of cohesionless soils;1. Deformation behavion at any stress system and fabric anisotropy and constitutive equation of sandy grounds. (1) By evaluating the fabric anisotropy and the relative magnitude of the intermediate principal stress appropriately, the deformation-strength characteristics of sand obtained by the trosional simple shear tests agreed well with that of the plane strain compression tests having the fixed principal stress axes. (2) An yield function, the extended Drucker-Prager's yield function, is formulated using explicitly the fabric tensor which is an index measure for representing the anisotropy of three-dimensional particle orientation. (3) A constitutive model for granular materials by which the general strain increments are directly related to the general stress increments is derived. The model proposed predicts the strains not only due to consolidation and shear, but also due to principal stress rotation.2. Evaluation of in-situ liquefaction strength of sand grounds. An evaluation method of liquefaction strength of sandy grounds was proposed based on an empirical correlation between the field performance observed during previons earthquakes and geological records.3. Undrained cyclic triaxial test methods. A co-operative test program of cyclic undrained triaxial tests was performed following the newly specified test procedures by 48 laboratories in Japan for Toyoura sand specimens. The scattering of the data was found mainly due to different specimen shape, different consolidation method and asymmetry in the cyclic stress amplitude.