Failure Mechanics of Geomaterials

Abstract

Geomaterials represent an important class of dissipative materials whose mechanical behavior is pressure, density, and fabric dependent. This constitutive characteristic together with the discrete particulate nature of the material leads to the manifestation of a rich variety of failure modes whose precise understanding is elusive within standard failure theories. The present chapter attempts to clarify this issue by invoking plasticity/damage phenomena in geomaterials and exploits their non-associated character in relation to rate-independent irreversible strains. The second-order work criterion provides a basic framework within which failure can be systematically treated as a divergence instability that leads to various forms, including localized and diffuse modes. This new interpretation considers the existence of a bifurcation domain and so-called instability cones whose generators denote the range of loading directions in stress space along which the material response is potentially unstable. As additional important characteristics, macroscopic failure is found to occur with an outburst of kinetic energy with the proper load control parameter in place, as demonstrated in discrete element computations. Finally, the failure analysis of in situ boundary value problems as in a rock and a soil slope is presented using the second-order work.