Hydro-Mechanical Properties of an Unsaturated Frictional Material

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CHAPTER 7. ANALYSIS AND INTERPRETATION OF THE EXPERIMENTAL
RESULTS
between saturations and suction. These parameters are difficult to measure or they are not
measurable at all (e.g. form parameter, ξ, material parameter, ζ, frustum number, ηf0).
7.3.2 Hysteretic Soil-Water Characteristic Curve Model by Feng & Fredlund
(1999), Pham (2003)
Experimental results of water content and suction values from loose Hostun sand specimen
carried out in the modified pressure plate apparatus were used for curve fit with Feng and
Fredlund’s (1999) model including the modifications proposed by Pham et al. (2003) (see
Eqs. 2.13 to 2.15). Experimental results and calculated results are presented in Fig. 7.11
and the parameters derived from residual analysis are given in Tab. 7.2. The model fits
the drainage curve well in the saturated zone and unsaturated zone, but differences between
calculation and experimental results can be observed in the residual zone. The imbibition
curve shows, that the calculated results are steeper than the experimental results. In the lower
part of the water content-suction relationship the experimental results are underestimated and
in the upper part the experimental results are overestimated by the calculated results.
Advantage of the model is, that the main drainage curve and only two measurements along
the main imbibition curve are necessary to predict the entire range of the main drainage-
imbibition loop. But using only two measurements points from the imbibition curve gives
not the best agreement for Hostun sand between measured and calculated results. Scanning
curves are not considered in the model.
Water content (%)
40
30
20
10
0
0.1 1 10 100
Suction (kPa)
results main drainage Experimental results main imbibition Pham et al. (2003) Experimental
Initial void ratio = 0.89
Figure 7.11: Experimental results of drainage and imbibition curve for loose specimen including
best fit derived from Pham’s model (2003)