ABSTRACT
Sand and other granular material particles tend to align along the bedding plane when deposited under gravity. Mechanical properties of materials pos-sessing such fabric anisotropy are thus naturally di-rection-dependent. For instance, Mahmood and Mitchell [1972]’s laboratory experiments found that fine crushed basalt specimens have significantly higher shear strength when sheared perpendicular to the bedding plane than that parallel to the bedding plane. Plane-strain compression experiments on specimens with the bedding plane at arbitrary angles also found the failure stress ratio to be dependent on the orientation of the bedding plane with respect to the principal stress direction [Oda et al. 1978; Oda 1981; Tatsuoka et al. 1986, 1990]. An appropriate failure criterion that takes the effects of fabric ani-sotropy into account plays an important role in the design of numerous geo-structures. The current paper reviews our effort to prove that the extension of
direction-dependent strength theory for sands to include the effects of fabric anisotropy should be based on the original Coulomb criterion, not the MohrCoulomb criterion. We lay out the reasoning behind this argument and propose testable hypotheses in section 2. In section 3, we preliminarily prove the proposed idea by studying a virtual granular material simulated using the discrete element method (DEM).After the “proof of concept”, section 4 presents a full-blown laboratory study that investigates direction-dependent strength of three real sands with different degrees of fabric anisotropy and confirms the DEM findings.
