PLANE-STRAIN INSTABILITY OF SATURATED POROUS-MEDIA

Herein we investigate the plane-strain instability of rectangular bloc ks that are made of porous materials saturated with a fluid. We model the material behavior with rate-type constitutive equations, and study instability generated by the interaction of nearly incompressible sol id and fluid constituents. Our investigation, although it applies to a broad range of materials, is limited to hypoelastic and elastoplastic models. Elastoplastic models are found to undergo two-phase instabili ty even though the solid phase remains stable. Two-phase instability i s more likely to occur in contractant hardening materials than in dila tant materials. Its emergence is triggered by the solid-fluid interact ion, and is delayed by the grain-fluid compressibility. Two-phase inst ability also takes place in dilatant materials, but is less catastroph ic than in contractant materials. The present analysis is useful for d istinguishing the physical from the artifical origins of instabilities , which is an important issue in the numerical solutions of soil-lique faction problems.