Hydro-Mechanical Properties of an Unsaturated Frictional Material

108 CHAPTER 5. MATERIAL USED AND EXPERIMENTAL PROGRAM
tigation of hydraulic behavior) and the determination of stiffness behavior as well as collapse
potential (investigation of mechanical behavior). Element tests (in the modified pressure
plate apparatus and in the controlled-suction oedometer cell) and benchmark tests (in the
sand column testing device I and II) were performed and compared.
Steady state tests were performed in a modified pressure plate apparatus. The influence
of loading path history (drainage process, imbibition process, scanning process) and void
ratio (loose specimen e0 = 0.89, dense specimen e0 = 0.66) on the soil-water characteristic
curve was examined. Additionally the influence of net stress on the shape of the soil-water
characteristic curve of loose specimen was investigated. Based on axis-translation technique
measurements of the soil-water characteristic curve were directly obtained. The results were
used to predict indirectly the unsaturated hydraulic conductivity (statistical models).
Steady state as well as transient state tests were performed using a large scale column
testing device (column device I). Several drainage and imbibition curves were measured to
investigate the influence of the loading path history (drainage process, imbibition process,
scanning process), void ratio (loose specimen e0 = 0.89, dense specimen e0 = 0.66) and water
flow condition on the shape of the soil-water characteristic curves. Results derived from the
transient state test were used for direct determination of the unsaturated hydraulic conduc-
tivity by instantaneous profile method. However, the unsaturated hydraulic conductivity also
was estimated indirectly from the steady state and transient state test results using indirect
models.
Transient state tests were performed also using a small scale column testing device (col-
umn device II). Drainage tests were performed to investigate the influence of the void ratio
(loose specimen e0 = 0.89, dense specimen e0 = 0.66) and the water flow condition on the
shape of the soil-water characteristic curve. Similar to the steady state tests the unsaturated
hydraulic conductivity was indirectly estimated. In both experiments, the column device I
and column device II experiments, TDR sensors as well as tensiometer sensors measurements
were conducted. These measurements gave information about the water content versus time
relationship and the pore-water pressure versus time relationship during testing procedure.
Negative pore-water pressure measurements (matric suction) linked to the appropriate water
content measurements yield directly to the soil-water characteristic curve.
One dimensional compression and rebound tests investigated the mechanical behavior of
unsaturated loose (e0 = 0.89) and dense (e0 = 0.66) sand specimen. Tests were performed
under constant suction condition in a controlled-suction oedometer cell (Romero 1999). For
different initial conditions the collapse behavior of Hostun sand was studied. These specimens
were prepared for loose conditions.
Experiments performed for the investigation of the hydro-mechancial behavior of unsat-
urated Hostun sand are briefly summarized in Tab. 5.4 and 5.5, where the conditions of
the flow experiments and the performed measurements are summarized. Tab. 5.6 gives an