Hydro-Mechanical Properties of an Unsaturated Frictional Material

2.6. IDENTIFICATION OF HYDRAULIC FUNCTIONS USING INVERSE
PROCEDURES
Fig. 2.27 shows results of indirectly estimated hydraulic conductivity functions using the
above introduced statistical models in correlation with the soil-water characteristic curves
given in the previous section. The model by Fredlund et al. (1994) is restricted to use only
in combination with their proposed soil-water characteristic curve. The relative hydraulic
conductivity versus effective saturation as well as unsaturated hydraulic conductivity versus
suction are shown.
2.6 Identification of Hydraulic Functions using Inverse Procedures
The use of inverse modeling techniques has increased in the past years. In comparison to the
determination of hydraulic functions using conventional experiments performed under equilib-
rium condition inverse modeling is a fast method to estimate unsaturated hydraulic functions
using measurements from outflow and inflow experiments. With increase in computer power
inverse methods based on parameter optimization for soil hydraulic functions have been de-
veloped for estimation of unsaturated hydraulic properties. Traditionally experimental results
from following inflow/ outflow tests were utilized for inverse procedures:
- one-step method including water outflow data
- one-step method including water outflow data plus pressure head measurements
- multistep method including water outflow data
- multistep method including water outflow data plus pressure head measurements
- continuous flow method including flow data and pressure head or water content mea-
surements
The set up of the experiment as well as the boundary conditions have to be selected carefully to
guarantee unique and robust identification of the unsaturated hydraulic parameter set. In the
last years several researchers applied the inverse approach to one-step outflow experiments, but
encountered problems with the non-uniqueness of the solution. Differences between inversely
determined and independently measured data were found. Carrera & Neumann (1986) defined
criteria of uniqueness, stability and identifiability for inverse problems. The use of inverse
methods for the determination of unsaturated flow parameters using transient experimental
data was first reported by Zachmann et al. (1981, 1982). State of the art report for inverse
modeling of flow experiments is given in Durner et al. (1999).
- Inverse procedure using experimental results derived from the One-step method
Kool et al. (1985a) investigated the feasibility of the determination of unsaturated
hydraulic functions using cumulative outflow measurements from one-step pressure
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