Hydro-Mechanical Properties of an Unsaturated Frictional Material

62 CHAPTER 2. STATE OF THE ART
Vertical strain (-)
0.000
0.002
0.004
0.006
0.008
0.010
Logarithm vertical strain (-)
-4
-5
-6
-7
-8
Experimental results
loading path
Experimental results
unloading path
0.1 1 10 100 1000
Vertical net stress (kPa)
Regression loading path
Regression unloading path
-4 -3 -2 -1 0 1
Logarithm stress ratio (-)
Figure 2.29: One dimensional compression and rebound results for Hostun sand and appropriate
regression functions
well as matric suction (Alosnso et al. 1987, Delage 2002, Rahardjo & Fredlund 2003). When
dealing with experiments on unsaturated soils special test features are required, e.g. ceramic
disk for separation of air phase and water phase, equipment for application of pore-air pressure
as well as pore-water pressure for application and control of matric suction. Among others,
oedometer cells for investigation of unsaturated soils were developed by Kassiff & Shalom
(1971), Escario & Saez (1973), Romero (1999), Rampino et al. (1999). Most of these cells
were used to investigate the volume change behavior of unsaturated silts or clays. Several
authors (Cui & Delage 1996, Rahardjo & Fredlund 2003) have been demonstrated that the
suction has a significant influence on the mechanical unsaturated soil behavior of cohesive
soils as volume change and stiffness. For instance Cui & Delage (1996), Rampino et al. (2000)