Doctor of Philosophy (PhD)
Department of Civil & Environmental Engineering
Cavity expansion/contraction problems have attracted intensive attentions over the past several decades due to its versatile applications, such as the interpretation of pressuremeter/piezocone penetration testing results and the modelling of pile installation/tunnel excavation in civil engineering, and the prediction of critical mud pressure required to maintain the wellbore stability in petroleum engineering. Despite the fact that various types of constitutive models have been covered in the literature on this subject, the soils and/or rocks were usually treated as isotropic geomaterials.
In recognition of the above fact, this research makes a substantial extension of the fundamental cavity expansion theory by considering the derivations of analytical solutions of the soil anisotropies (Dafalias, 1987), which include the initial K0 consolidation anisotropy developed in the deposition process and the stress-induced anisotropy as a results of the external loadings. It is found that the undrained/drained cavity expansion boundary value problems both can be eventually reduced to solving a system of first-order ordinary differential equations in the plastic zone, with the radial, tangential, and vertical stresses in association with the three anisotropic hardening parameters and specific volume (for the drained condition only) being the basic unknowns. Extensive parametric studies are then analyzed regarding the influences of K0 consolidation anisotropy (including also the subsequent stress-induced anisotropy) and past consolidation history (OCR) on the cavity responses during the expansion process.
To solve the practical problems, this research develops an implicit integration algorithm for such anisotropic modified Cam Clay soil model, using the standard return mapping approach (elastic predictor-plastic corrector). The finite element formulation essentially involves simultaneous equations with stress components and state variables and as the basic unknowns to be solved. The integration algorithm developed for this model is thereafter implemented into the commercial program, ABAQUS, through the interface of the user defined material subroutine (UMAT). Numerical simulations have been conducted to solve the undrained and drained cylindrical cavity expansion problems as well as miniature piezocone penetration test for the purpose of validation, and to analyze pile setup phenomenon and tunnel excavation considering soil consolidation as the illustrative applications.
Liu, Kai, "Analytical and Numerical Modeling of Cavity Expansion in Anisotropic Poroelastoplastic Soil" (2019). LSU Doctoral Dissertations. 4899.