A Framework for Coupled Solid-Deformation/Fluid-Diffusion
Analysis of Variably Saturated Slopes: Mathematical Developments
and Numerical Simulations of Coos Bay Experimental Catchment

Ronaldo I. Borja1, Joshua A. White2, and Azad Koliji3
Department of Civil and Environmental Engineering
Stanford University
Despite decades of extensive slope stability model development, the fundamental controls connecting the hydrologic and geotechnical processes triggering slope failure are still not well quantified. This lack of understanding is a direct result of the simplified physics in current models, with the omission of the effect of partial saturation from slope stability calculations. In this work, we develop and test a 3D physics-based slope deformation model that couples the solid deformation with fluid flow processes in variably saturated slopes. We also assess the capability of the model to predict stresses and deformation necessary to trigger slope failure. The platform selected for the studies is continuum modeling with the finite element method, combining inelastic modeling in the finite deformation regime with stabilization to allow low-order interpolation of the displacement and pore pressure fields. We compare and contrast the capabilities of classical critical state models with a double porosity model for modeling the mechanical response of unsaturated porous media, where the latter constitutive model accounts for the presence of mobile and stagnant water phases. The coupled model is tested with comprehensive and exhaustive data from Coos Bay (CB1) experimental catchment in Oregon, as well as with the numerical results of recently conducted simulations on the same catchment using an Integrated Hydrology Model. The highly instrumented CB1 slope failed as a large debris flow in November 1996, providing large volumes of data with which to compare the simulation results.
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1Professor
2Doctoral Student
3Post-Doctoral Scholar


Prof. Ronnie Borja works in theoretical and computational solid mechanics and geomechanics. His research includes developing strain localization models
for geomaterials, modeling lateral flow and liquefaction-induced ground movement, finite element modeling of dynamic soil-fluid-structure
interaction phenomena, developing nonlinear models for earthquake site response analysis, and modeling multi-phase and multi-scale phenomena in
structural and solid mechanics. His current research projects include the investigation and mathematical modeling of brittle faulting and cataclastic
flow in high-porosity rocks using fracture mechanics, bifurcation theory, and embedded discontinuity finite element techniques. Professor Borja has
been involved in a project for the intervention and restoration measures for the Tower of Pisa, and in the finite element modeling of the dynamic
soil-foundation-structure interaction response of the South Memnon Colossus in Luxor, Egypt.