Hydro-Mechanical Properties of an Unsaturated Frictional Material

6.4. VOLUMETRIC BEHAVIOR 129
Depth (cm)
0
10
20
30
40
50
6
4
state 30 min 120 min 180 min Initial
min 300 min 360 min 420 min 240
Pore - water pressure (kPa)
2
0
-2
-4
-6
0
10
20
30
40
50
50
Volumetric water content (%)
40
30
20
10
1st drainage
Loose specimen
Initial void ratio = 0.89
Figure 6.14: Pore-water pressure and volumetric water content profiles for 1 st drainage process
(loose specimen)
6.4 Volumetric Behavior
For determination of the mechanical behavior of unsaturated Hostun sand stress-strain re-
lationships derived from one dimensional compression rebound tests and collapse tests were
investigated. The results are give in the section below.
6.4.1 Stress-Strain Relationship
Experimental results from one dimensional compression and rebound tests are presented in
Fig. 6.15 for loose specimens and in Fig. 6.16 for dense specimens. Volumetric strain versus
applied vertical net stress as well as void ratio versus applied vertical net stress results are
given in the diagrams. For sands the following typical observations in the stress-strain curve
are made (Lambe & Whitman 1969):
- Observation during loading path:
As can be seen in the stress strain diagrams in Figs. 6.15 and 6.16 the sand becomes
stiffer with increasing vertical stress. As the stress increases within the soil sample
loose arrays collapse followed by denser arrays. Each movement results in a stiffer
packed specimen and thus decreasing void ratio. With increasing stress the stress-strain
curvature becomes concave to the strain axis resulting from fracturing of individual sand
particles. Whereas sliding between particles occurs at all stress levels, fracturing and
crushing becomes increasingly important with increase in vertical stress.
0