Hydro-Mechanical Properties of an Unsaturated Frictional Material

8.2. SOIL-WATER CHARACTERISTIC CURVE MODEL 175
Volumetric water content (%)
Volumetric water content (%)
50
40
30
20
10
0
40
30
20
10
0
Suction (kPa)
results New model curve fit Experimental
Transient state column test I Loose specimen Initial void ratio = 0.89 1st drainage Flow rate = 30 ml/min TDR/T 70 mm
50 0 1 2 3 4
0 1 2 3 4
drainage Flow rate = 100 ml/min TDR/T 160 mm 2nd
Suction (kPa)
Figure 8.3: Experimental drainage results from several depth and new SWCC model best fit
(loose specimen, transient state sand column test)
corresponding parameters and the linear regression coefficient R 2 are given in Tab. 8.1. From
the first view it seems that the proposed model fits the experimental results well. However,
later on the model validation procedure is used wether or not the model is suitable to fit the
suction-water content data.
Now it is tried to extend the proposed model in this way, that it also could be used for
scanning imbibition curve fit. It is focused on a model that describes with a single set of
parameters several scanning imbibition curves. The fact that the suction-volumetric water
content profiles of θ versus ψ (respectively the profiles of saturation S versus suction ψ) vary
with depth, that leads to different initial imbibition suction s0, confirms that any functional
description of the process will need to include the variable s0. Further insight into the ap-
propriate function to use can be obtained by separately modeling each cross-section of the
experimental data using the proposed model and then relating the individual models to one
another. Examining plots of the estimated parameters versus s0 roughly indicates how the
suction measurement should be incorporated into the model of the data. Regression curves to
the cross-sections data for the 1 st imbibition as well as the 2 nd imbibition process at several