Hydro-Mechanical Properties of an Unsaturated Frictional Material

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CHAPTER 7. ANALYSIS AND INTERPRETATION OF THE EXPERIMENTAL
RESULTS
state tests. In the unsaturated hydraulic conductivity versus volumetric water content curve
slight hysteresis was found for loose and dense specimens in the intermediate range.
7.5 Volumetric Behavior
To investigate the influence of suction on mechanical behavior of Hostun sand the stiffness
modulus, the compression as well as swelling index, the collapse potential and the preconsol-
idation pressure are determined from the experimental results.
7.5.1 Stiffness Modulus, Compression and Swelling Index
Test results from one dimensional compression rebound tests were presented in Figs. 6.15
and 6.16, where the applied vertical net stress is plotted versus volumetric strain and void
ratio for loose and dense specimen. 3D plots of the oedometer results for loose and dense
sand specimen are added in this section in Fig. 7.18. As already mentioned in Chapter 6 from
Figs. 6.15, 6.16 and Fig. 7.18 one can see that as anticipated the stiffness for dense specimen
is higher then for loose specimen.
The stiffness increases with matric suction from ψ = 1.5 kPa, 3.0 kPa and 20.0 kPa for
the tests carried out for dense specimen. Lowest stiffness results from the test with a matric
suction of ψ = 50.0 kPa, for the dry and the saturated specimen. Similarly to the dense
specimens for the loose one the lowest stiffness was calculated for the specimen with matric
suction ψ = 50.0 kPa, for the dry and the saturated specimen. With increase in matric suction
from ψ = 1.5 kPa to 20.0 kPa the stiffness is slightly increasing. Comparison of the results
from the unloading path of all tests one can state that, there is a similar behavior for all the
specimens.
Void ratio [-]
0.665
0.660
0.655
0.650
0.645
0.640
0.635
0.630
Matric suction [kPa]
1
10
100
1000
100
10
Vertical net stress [kPa]
1
Void ratio [-]
0.885
0.880
0.875
0.870
0.865
0.860
0.855
0.850
Matric suction [kPa]
1
10
100
1000
100
10
Vertical net stress [kPa]
Figure 7.18: 3D plots of oedometer test results for dense (left) and loose (right) specimen
1