Hydro-Mechanical Properties of an Unsaturated Frictional Material

130 CHAPTER 6. EXPERIMENTAL RESULTS
Vertical strain (-)
Void ratio (-)
0.000
0.005
0.010
0.015
0.020
0.885
0.880
0.875
0.870
0.865
0.860
0.855
Applied suction:
kPa 3.0 kPa 20.0 kPa 50.0 kPa 1.5
1·106 kPa Reihe4
1 10 100
0 kPa
1000
0.890
1 10 100 1000
Vertical net stress (kPa)
specimen Initial void ratio = 0.89 Loose
Figure 6.15: Experimental results of one dimensional compression rebound test for constant
suction condition (loose specimen)
- Observation during unloading path:
The unloading path shows that the initial strain is not reached again. The strain from
sliding between particles or fracturing is an irreversible process. Some reverse sliding
during unloading is observed. This is due elastic energy within few particles.
A comparison between the experimental results of the loose specimen and the dense specimen
in Fig. 6.15 and Fig. 6.16 shows that as anticipated the stiffness for dense specimens is
higher then for loose specimens. The difference in void ration during loading path is larger
for the loose specimens with approximately ∆e = 0.025 than for the dense specimens with
approximately ∆e = 0.015, which indicates a higher stiffness for the dense one. From the test
results for both loose and dense specimens it is observed, that the change in void ratio for
the specimens with applied suctions up to ψ = 20 kPa is smaller than for the dry as well as
saturated (S = 1) specimens. The results of the test with applied suction ψ = 50 kPa are close