Hydro-Mechanical Properties of an Unsaturated Frictional Material

110 CHAPTER 5. MATERIAL USED AND EXPERIMENTAL PROGRAM
(see Fig. 6.1). To investigate the hydraulic behavior of unsaturated sand initially saturated
loose and dense specimens were drained in several predetermined suction steps up to 50 kPa
and wetted up to 0.1 kPa. Scanning curves were determined by further drainage up to:
- 1.7 kPa, imbibition up to 0.6 kPa and drainage to 1.7 kPa (loose specimen)
- 2.2 kPa, imbibition up to 0.8 kPa and drainage to 2.2 kPa (loose specimen)
- 2.4 kPa, imbibition up to 1.0 kPa and drainage to 2.4 kPa (loose specimen)
- 1.9 kPa, imbibition up to 0.2 kPa and drainage to 1.9 kPa (dense specimen)
- 2.4 kPa, imbibition up to 0.7 kPa and drainage to 2.4 kPa (dense specimen)
- 2.6 kPa, imbibition up to 1.3 kPa and drainage to 2.6 kPa (dense specimen)
For each loose and dense packed Hostun sand 3 saturated specimen were prepared to determine
the scanning imbibition and drainage curves.
To investigate the influence of net stress on the hydro-mechancial behavior of unsaturated
sand loose specimens were loaded with 10 kPa and 20 kPa before saturating the specimen.
Then suction values up to 50 kPa (drainage process) were applied and suction values up to
0.1 kPa (imbibition process) were applied.
5.4.2 Tests Performed using Sand Column I
Steady state experiments as well as transient state experiments were carried out using the
large scale column testing device I. Saturated loose and dense specimens with a height of
about 540 mm were prepared. Starting with an initially water saturated specimen, the sand
was dried and wetted following different paths. The outflow and inflow of water from the
sand sample was induced by increasing and decreasing the water content or saturation using
the electronic pump attached to the lower water reservoir.
In the steady state test successive 1000 ml were removed (drainage process) from the
initially saturated specimen and injected to the specimen (imbibition process). When no
changes in measurements of the TDR sensors and tensiometer sensors were observed equilib-
rium conditions in the sand specimen was achieved. Next 1000 ml were withdrawn from the
sand specimen, viz versa injected to the specimen. From the loose specimen with initially
18000 ml in the pores 10 times 1000 ml were removed and 8 times 1000 ml were injected.
From the dense specimen with initially 17000 ml in the pores 8 times 1000 ml were removed
and 8 times 1000 ml were injected. During drainage process water was pumped out successive
until the water level reached the bottom of the specimen. During imbibition process water
was pumped into the specimen until the water level reached the top of the specimen. The
loading history of the steady state experiment is given in Fig. 5.10.