Hydro-Mechanical Properties of an Unsaturated Frictional Material

128 CHAPTER 6. EXPERIMENTAL RESULTS
suddenly applied to an initially saturated specimen) it seems, that the parameters as air-entry
value, residual suction, residual water content and water-entry value are similar for the loose
specimens and respectively for the dense specimens.
6.3 Unsaturated Hydraulic Conductivity
The unsaturated hydraulic conductivity was directly determined using suction and also volu-
metric water content measurements from the transient state sand column test I. Exemplary
pore-water pressure (hydrostatic pressure has positive sign and matric suction has negative
sign) and also exemplary volumetric water content profiles are presented in Fig. 6.13 for initial
drainage process and in Fig. 6.14 for 1 st drainage process of loose specimen. Measurements
every 20 th minutes are presented for several depths. Fig. 6.13 presents the initial condition
which is a fully saturated specimen. The tensiometer sensors measure the hydrostatic pres-
sure (positive pore water pressure) of water that shows a linear distribution in the specimen.
The TDR sensors measure the volumetric water content that is constant along the column.
Fig. 6.14 also presents a saturated specimen with a linear distributed positive pore water
pressure. But after 1 st imbibition process air remains in the pores and therefore full satu-
ration of the specimen is not reached (θ ′ s = 39%) as given in the volumetric water content
profile. Only the bottom TDR sensor is located in the saturated zone through the experiment
(θs = 46%). Both Figures show with outflow of water decreasing pore water pressure and
decreasing volumetric water content first in the top part and then in the bottom part of the
specimen.
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
Initial drainage
Loose specimen
Initial void ratio = 0.89
Figure 6.13: Pore-water pressure and volumetric water content profiles for initial drainage
process (loose specimen)
0