Hydro-Mechanical Properties of an Unsaturated Frictional Material

6.5. SUMMARY 133
ratio of ∆e = 0.0020 for saturation at σ = 25 kPa. Regarding the stiffness behavior before
and after the saturation process it seems, that before saturated condition in the specimen the
stiffness is higher. But calculations of compression index and stiffness modulus are required
for proper conclusions. Results of the compression index and stiffness modulus are presented
later in Chapter 7.
6.5 Summary
This chapter presents the results derived from the experiments performed. The experimental
results from the column testing devices (i.e. volumetric water content and pore-water pressure
versus time results and suction-water content results), the modified pressure plate apparatus
(i.e. cumulative water outflow/inflow data, changes in void ratio and soil-water characteristic
curves) as well as the controlled-suction oedometer cell (i.e. strain versus vertical net stress,
void ratio versus vertical net stress) are presented and discussed.
The investigations on Hostun sand performed in the modified pressure plate apparatus
and in the sand column testing devices I an II show, that the void ratio as well as the loading
path direction (i.e. drainage or imbibition path) influence its hydraulic behavior. Derived
soil-water characteristic curves established from steady state approach and transient state
approach show quantitative similar behavior. The influence of net stress on the hydraulic
behavior of unsaturated sand is found to be negligible. All cells enable to measure directly
the soil-water characteristic curve. The unsaturated hydraulic conductivity can be directly
determined using pore-water pressure and volumetric water content profiles measured during
sand column testing devices I experiments.
The investigations carried out in the controlled-suction oedometer cell show, that not only
the void ration but also the suction influences the stiffness behavior of unsaturated Hostun
sand. The collapse potential was found to be small.