Cracks, bifurcation and shear bands propagation in saturated clays

Abstract

Discontinuities in the form of cracks or fissures and inclusions are often present in natural clays. They serve as stress concentrators when loads are applied to the material. Such concentrations result in cracks advancing, often surrounded by and preceded by a propagating damage zone. As cracks propagate, the damage may be in the form of one or more shear bands, which may play the part of new stress concentrators and blunt the action of the original crack. This Paper examines some of the phenomena associated with cracks in over-consolidated clays and normally consolidated clays. Differences between isotropic and anisotropic materials, and the level at which serious modifications take place in the fabric of the material are noted. The influence of the cracks and the shear bands on the kinematics and strength of the test specimens is discussed. Des discontinuités sont souvent présentes, sous forme de fractures, fissures et inclusions, dans les argiles naturelles. Elles jouent le rôle de concentrateurs de contrainte lorsque des charges sont appliquées sur le matériau. De telles concentrations se traduisent par une progression des fissures, souvent entourée et précédée par une zone d'endommagement. Lorsque les fissures se propagent, l'endommagement peut apparaître sous forme d'une ou plusieurs bandes de cisaillement qui peuvent jouer le rôle de nouveaux concentrateurs de contrainte et réduire l'action des fissures initiales. L'article étudie quelques uns des phénomènes associésà la fissuration dans des argiles surconsolidées ou normalement consolidées. Des différences entre matériaux isotropes et anisotropes, ainsi que le niveauà partir duquel des modifications importantes apparaissent dans la texture, ont été observés. L'influence des fissures et des bandes de cisaillement sur la cinématique et la résistance des échantillons d'essai est discutée.

Non-coaxiality of strain increment and stress directions in cross-anisotropic sand

“…Similar testing and analyses have also been performed on clay (e.g. Broms and Casbarian, 1965;Saada and Baah, 1967;Hicher and Lade, 1987;Saada et al, 1994;Frydman et al, 1995;Hong and Lade, 1989a and b;Lade and Kirkgard, 2000;Nishimura et al, 2007). Lade et al, (2009) showed that modeling the observed behavior by an isotropic, plastic hardening soil implies that the two sets of directions coincide during stress rotation, but loading along the principal axes of an anisotropic material will also result in coincidence of principal stress axes with principal strain increment axes.…”

Progressive failure of a constrained creeping landslide

“…Strain localization and propagation of shear bands (few millimetre thick zones of intense shearing, where shear strength decreases to residual value) take place in soils exhibiting strain softening (Palmer & Rice 1973;Vardoulakis et al 1981;Saada et al 1994;Puzrin & Germanovich 2005;Saurer & Puzrin 2011). In a strain-softening material (figure 9), shear strength t * on the slip surface drops from the peak t p to residual value t r when the shear strain g in the shear band reaches the critical value of g r .…”

DEM analysis of the crack propagation in brittle clays under uniaxial compression tests

“…Several authors have studied the mechanics of crack propagation in brittle materials such as stiff clays [13][14][15][16][17][18][19] and cemented sands [20]. These authors used LEFM to analyze the mechanics of crack propagation and failure of those materials.…”