Hydro-Mechanical Properties of an Unsaturated Frictional Material

7.2. SOIL-WATER CHARACTERISTIC CURVE 143
Volumetric water content (%)
Volumetric water content (%)
50
40
30
20
10
0
θs= 40% θs=46%
specimen - drainage Loose specimen - imbibition Dense specimen - drainage Dense specimen - imbibition Loose
0.1 1 10
ψaev= 1.4 kPa (loose)
ψaev= 1.9 kPa (dense)
100
2.1 kPa (loose)
Suction (kPa)
kPa (dense) θr= 5%, ψr= 2.8 kPa (loose)
θr= 2%, ψr= 3.3 kPa (dense)
50
θs=θ's
40
ψwev= 2.6 ψwev=
41% ψaev= 1.2 kPa ψaev= 1.9 kPa
θs= 46% θs=
30
20
10
0
0.1 1 10 100
Suction
θr= 6%, ψr= 3.0 kPa
(kPa) 5%, ψr= 2.7 kPa Loose specimen Initial void ratio = 0.89 Dense specimen
θr=
void ratio = 0.66
Figure 7.4: Influence of void ratio on the shape of the soil-water characteristic curve (steady
state tests)
Initial
derived from modified pressure plate apparatus and the initial drainage curve derived from
sand column test I. As can be observed from the curves the void ratio is influencing the shape
of both, the drainage and the imbibition curve. The saturated volumetric water content of
the loose specimens is larger then for the dense specimens (θs,loose > θs,dense). Here the larger
voids of the loose specimen retain larger amount of water. Overall behavior is that with
decreasing void ratio the soil-water characteristic curve is shifting to slightly higher suction
values. This leads to higher air-entry value, residual suction as well as residual volumetric
water content during drainage path and also higher water-entry value during imbibition path.
Due to the smaller voids in the dense specimen the water is retained up to higher suction
values (ψaev,dense > ψaev,loose) when draining the saturated specimen. However, this is also
causing higher residual volumetric water contents (θr,dense > θr,loose) for the dense specimens.
When wetting the specimen the smaller voids of the dense specimens do absorb water at
slightly higher suction values than loose specimens (ψwev,dense > ψwev,loose). The saturated
volumetric water content θs is reached first for the dense specimen.