Hydro-Mechanical Properties of an Unsaturated Frictional Material

Chapter 9
Numerical Simulation of Column
Test by FEM
9.1 General
The investigation presented in the following chapter shows numerical simulations. Boundary
value problem is solved and compared to the experimental results. Numerical investigation
of drainage as well as imbibition processes of experiments carried out in the sand column I
under transient state condition are performed.
Two approaches are discussed, that are carried out using suction-water content parameters
directly derived from transient state test (sand column test I) and from steady state test
(modified pressure plate apparatus), that is classical method for prediction of suction-water
content parameters used for numerical investigation. The aim is to find reliable predictions on
unsaturated flow including the phenomena of hysteresis and entrapped air, which are found
to be significant for the experiments performed in the sand column test I. Therefore following
requirements to the numerical simulation are necessary:
- Simulation including hysteresis behavior.
- Simulation including scanning behavior.
- Simulation considering the phenomena of entrapped air.
The numerical simulations in this work are carried out with the multi-phase flow module
of the numerical simulator MUFTE-UG (Multiphase Flow Transport and Energy model-
Unstructured Grids). The balance equations for the two phases are solved fully coupled
using on a node-centered Finite-Volume discretization in space, the BOX-scheme (Bastian
et al. 1997, Helmig 1997, Huber & Helmig 1999). A backward-difference Euler scheme is
applied for the time discretization. The resulting non-linear system of equations is solved
with a quasi Newton-Raphson scheme, where the linear system of equations is handled with a
BiCGStab (stabilized biconjugate gradient) scheme utilizing a V-multi-grid cycle as pre- and
post-smoother.
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