Hydro-Mechanical Properties of an Unsaturated Frictional Material

112 CHAPTER 5. MATERIAL USED AND EXPERIMENTAL PROGRAM
Schematic water table
ml/min Top of the specimen 30
Loading step ml/min 1 st Drainage
30
100 ml/min
ml/min Initial Drainage
2 nd Drainage
1 st Imbibition
2 nd Imbibition
100 ml/min Bottom of the specimen
Figure 5.11: Loading history of transient state experiment in column testing device I for loose
and dense specimen
30
5.4.3 Tests Performed using Sand Column II
The column testing device II was used to conduct transient state tests on loose and dense
specimen. Drainage tests were performed by applying an air-pressure of approximately 3.5 kPa
from the top of the cell to the initially water saturated specimen.
5.4.4 One Dimensional Compression and Rebound Tests
One dimensional compression and rebound test were performed in a controlled-suction
oedometer cell. Tests were carried out for loose specimen with an initial void ratio of
e0 = 0.89 ± 0.005 and dense specimen with an initial void ratio of e0 = 0.66 ± 0.005. The
precision for measured deformation is 0.001 mm and 0.6% of the absolute value for stresses
(both vertical stress and air pressure).
Special attention was given to the error estimation related to the vertical net load. Cor-
rection was applied to the measured vertical net stresses due to shear stresses between the
oedometer ring and the soil sample. Both frictional (fixed ring, triangular distribution of
horizontal stress: σ max
h
= (1 − sin φp)σv, loose: φp = 34 o , dense: φp = 42 o (Schanz 1998))
and cohesional effects (derivation of capillary cohesion from soil-water characteristic curve)
were taken into account following (Fredlund et al. 1996b). Loose and dense specimens with
a predetermined suction value were prepared. Suctions were applied using suction mode test
(ψ = 1.5 kPa and ψ = 3 kPa) and pressure mode test (ψ = 20 kPa and ψ = 50 kPa) to
the sand samples and kept constant during the loading and unloading path. Specimens were
loaded up to 200 kPa and then unloaded to 2 kPa. Loading history and loading steps of the
one dimensional compression and rebound tests are given in Fig. 5.12 as well as Tab. 5.8.