Stiff clays and mudstones: fundamentals, progressive failure and deep underground excavations

The subject of this contribution is the hydromechanical behaviour of stiff clays and mudstones, i.e. geological materials in which fine grained particles predominate. It is especially focussed on argillaceous materials that are intermediate between soils and rocks not only with respect to strength but also in terms of porosity and compressibility. Because of space limitations, only sorne salient aspects of the behaviour are outlined herein. First, sorne general aspects of the mechanical behaviour are high1ighted, afterwards the issues of brittleness and progressive failure are addressed and finally sorne observations of their hydromechanical response in underground excavations are presented