FABRIC TENSOR FOR DISCONTINUOUS GEOLOGICAL MATERIALS

ABSTRACT Geometrical property (fabric) of discontinuity in geological materials is discussed in terms of (1) position and density, (2) shape and dimension and (3) orientation of related discontinuities such as joint, fault and discrete particle. By taking into account these geometrical elements, a unique measure called fabric tensor Fij is definitely introduced to embody the fabric concept without loss of generality. The first invariant of Fij is important as an index measure to evaluate the crack intensity which is related to the number and dimension of cracks. Porosity of granite is shown to be an index measure equivalent to the first invariant of Fij According to uniaxial compressive tests on gypsum plaster samples with two-dimensionally oriented cracks and granite samples, the logarithm of the first invariant of Fij is linearly related to their uniaxial compressive strength. A measure Γ which is related to the second invariant of the deviatoric part of Fij shows a distance from an isotropic fabric. So, it is expected to be an index to measure the degree of anisotropy due to preferred alignment of discontinuity. The principal axes of Fij are identical to the principal axes of fabric anisotropy. There is no doubt that Γ and the principal axes are important in the analysis of anisotropic discontinuous geological materials.

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