Structural weaknesses in rocks and rock masses Tentative classification and behaviour

The paper reviews the chief structural weaknesses of rocks and rock masses that is the departures from the properties of an ideal material, continuous, homogeneous, isotropic, including a neutral state of stress and the permanence of these properties along time, whatever the environment. Two simple cases of heterogeneity are fo-cussed : the spherical inclusion, and the sandwich, that is superposition of parallel beds. More general cases are randomly distributed spherical inclusions and lenticular formations. Use is made of series and parallel assemblies. A better knowledge and understanding of the influence of structural defects on mechanical behaviours of soils and rocks raises the question of more naturalistic description of these defects. Here is the true place of geology in soil and rock mechanics.