Axisymmetric Instability of Fluid Saturated Pervious Cylinders

The emergence of two-phase instability is investigated analytically for the axisymmetric cylinders made of a pervious solid matrix with pores filled with an interstitial fluid. General analytical solutions are derived for a broad range of constitutive models, and are illustrated for a few specific types of solids. For particular combinations of stresses and material moduli, saturated hypoelastic and elastoplastic solids are found to undergo two-phase instability, whereas their dry solid matrices remain stable. Two-phase instability can emerge within stable single-phase solids due to the interaction between solid matrix and fluid flow. The present analysis provides general analytical solutions useful for investigating the instabilities of axisymmetric soil samples subjected to the undrained triaxial tests of geomechanics.