Hydro-Mechanical Properties of an Unsaturated Frictional Material

24 CHAPTER 2. STATE OF THE ART
where: S is the saturation and Sr is the residual saturation. In case of silt, the shape
of the unsaturated hydraulic conductivity function is explained. It is assumed the initial
condition is a water saturated specimen, where the suction is equal to zero and the volumetric
water content is θs = 48 %. The soil matrix is saturated with water and the saturated
conductivity, that is the maximum conductivity (maximum cross sectional area for water
to flow is available), is equal to ks = 1 · 10 −7 m/s. Consequently the conductivity of air
is equal to zero at this state. Until reaching the air-entry value the soil retains nearly all
amount of water (see also suction water content relationship) that causes only a slight decrease
in unsaturated hydraulic conductivity. Desaturation commences when passing the air-entry
value, where air starts to enter the soil largest pores. With increasing suction the pore
Volumetric water content (%)
Hydraulic cond. (10 -4 m/s)
Relative conductivity (-)
70
60
50
40
30
20
10
0
0.01
0.001
0.0001
Sand
0.0001 0.001 0.01 0.1 1
1
Suction (MPa)
0.1
1.0
0.8
0.6
0.4
0.2
0.0
0.0001 0.001 0.01 0.1 1
0.0 0.2 0.4 0.6 0.8 1.0
Volumetric water content (%)
Hydraulic cond. (10 -7 m/s)
Relative conductivity (-)
70
60
50
40
30
20
10
0
0.01
0.001
0.0001
θ s= 48
Silt
ψ AEV= 0.003 MPa
θ r= 10
0.0001 0.001 0.01 0.1 1
1
Suction (MPa)
0.1
1.0
0.8
0.6
0.4
0.2
0.0
k s= 1·10 -7 m/s
0.0001 0.001 0.01 0.1 1
Suction (MPa)
0.0 0.2 0.4 0.6 0.8 1.0
Effective Saturation (-)
Volumetric water content (%)
Hydraulic cond. (10 -10 m/s)
Relative conductivity (-)
70
60
50
40
30
20
10
0
0.01
0.001
0.0001
0.0001
1
0.001 0.01 0.1 1
0.1
1.0
0.8
0.6
0.4
0.2
0.0
Clay
0.0001 0.001 0.01 0.1 1
0.0 0.2 0.4 0.6 0.8 1.0
Figure 2.14: Exemplary hydraulic functions (soil-water characteristic curve - top, hydraulic
conductivity function - middle, relative hydraulic conductivity function - bottom) for sand,
silt and clay