Although soils and rocks are both geomaterials, their behaviour under applied loads can be quite different. When it comes to strength and deformation, some of the major differences between rocks and soils are as follows:
• Soils are classic particulate media, and rocks can be seen as a disjointed continuum. There is a significant scale effect in rocks, which is not present in soils. The intact rock, with no structural defects (Figure 5.1a), can be treated as homogeneous and isotropic. On the contrary, the rock mass will often be heterogeneous and anisotropic due to the presence of discontinuities (Figure 5.1b). It can be seen in Figure 5.1b that the stability is better when the loads are applied vertically than horizontally. A highly disjointed or fractured rock (Figure 5.1c) can again be treated as an isotropic material, with a large number of randomly oriented discontinuities. In the case of soils, we generally treat them as homogeneous and isotropic. There are no scale effects in soils; irrespective of the extent considered, the behaviour is the same.