Hydro-Mechanical Properties of an Unsaturated Frictional Material

11.3. HYDRO-MECHANICAL BEHAVIOR 209
are similar to the results derived under steady state conditions. No significant dynamic
effect was found.
- Influence of net stress:
No significant influence from the applied net stress on the shape of the soil-water char-
acteristic curve was found.
Childs and Collis George (1950), Mualem´s (1976) and Fredlund and Xing’s (1994) model
were applied for further calculations of the unsaturated hydraulic conductivity. The experi-
mental results from the transient state tests, where volumetric water content and suction are
measured, were used to calculate the unsaturated hydraulic conductivity using the instan-
taneous profile method. This results are conform with those calculated indirectly by using
statistical model from Fredlund et al. (1994).
In the present work the experimental results were used to introduce a method for model
building, that is based on statistical assessment. As a result, a new soil-water characteristic
curve model was introduced, which accounts for scanning imbibition processes. The model is
simple in use and it was found that the observed values are conform to the predicted values.
Statistical techniques, i.e. graphical and numerical methods, support to use of the developed
model. Advantages and disadvantages of the proposed suction-water content model are:
+ The single model is a simple application and thus is simple in its usage.
+ The model is based on detailed statistical analysis.
+ Only 4 parameters (β1, β2, β31, β32) have to be determined. Parameter β0 is related to
the saturated water content and β3 is related to the residual water content.
- The proposed scanning model can not be used for scanning drainage curves.
The proposed soil-water characteristic curve model was successfully applied to the experimen-
tal results derived in the present investigation. Slight modifications may be necessary, when
using different type of sandy soils. To further upgrade of the new model, the consideration of
scanning drainage processes has to be included.
The mechanical behavior of unsaturated Hostun sand was investigated in one-dimensional
compression and rebound tests. The experimental investigation showed, that the compres-
sion index and thus the stiffness modulus are clearly influenced by suction during loading.
With increase in matric suction the compression index decreases and vice versa the stiffness
increases. After reaching an optimum value the compression index increases, that means the
stiffness modulus decreases again. The mechanical behavior under dry condition (S = 0) is
similar to the mechanical behavior under saturated condition (S = 1). No influence of suction
on the mechanical behavior during unloading path was found. Collapse potential was studied