Numerical Modeling of Unsaturated Soils Problems

M.D. Fredlund


Soils and Rocks, São Paulo, 39(1): 97-109, January-April, 2016 | PDF


Numerical modeling (finite element analyses) of saturated-unsaturated soils problems generally involves the solution of linear or nonlinear partial differential equations, PDEs. The soil properties for unsaturated soils usually take on a functional form that subsequently requires an iterative procedure to obtain a solution. Special numerical solution techniques are helpful (and in some cases necessary) in order to have confidence that the results of the numerical solution are accurate. The dynamic upgrade of the finite element mesh (and time steps) during the iterative solution process have proven to be of significant value in ensuring the proper convergence of the numerical solution. The unsaturated soil property functions are usually obtained through use of estimation procedures based on the measurement of the soil-water characteristic curve, SWCC. One or more estimation procedures have been proposed in the research literature for soil property functions for each physical process of interest in unsaturated soil mechanics. The numerical modeller must be aware of the relationship between the estimated soil property functions and the solution technique. Boundary conditions required when solving unsaturated soils problems often involve the assessment of moisture and thermal flux conditions computed from meteorological records. There are conditions and requirements that must be quantifiable when solving unsaturated soils problems. The estimation of the unsaturated soil property functions makes the solution of unsaturated soils problems more complex than those of saturated soils.

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