Structure of Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 10

Figure 2.6 Claystone, planar grain structure, Nuttlar (Germany)
If two planar structures with different orientations are present, the lines of intersec-
tion of both structures may form a linear grain structure, also referred to as “linea-
tion”.
From the rock mechanics point of view intact rocks can be classified with respect to
their grain structure. Most intact rocks can be related to a random and a planar grain
structure as represented by the models shown in Fig. 2.8. Intact rocks with a random
grain structure are most likely characterized by an isotropic behavior with regard to
deformability and strength. In contrast, intact rocks with a planar grain structure can
exhibit a marked anisotropy with respect to deformability and strength (Section 3.2).
With regard to rock engineering all intact rocks can be regarded as homogeneous
because the grains are very small compared to the dimension of an engineering struc-
ture.