Soil-Water Characteristic Curves for Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 243

plate of the cell has a high-air-entry ceramic disk and uses
the axis translation technique to apply various matric suc-
tion values.
Total suctions can also be controlled using the vapor cir-
culation from above a saturated salt solution (Fig. 5.83).
A coarse disk is substituted for the high-air-entry disk in
the base plate. Air at a constant relative humidity can be
circulated through the coarse disk. In this way, it has been
possible to apply extremely high suctions to a soil specimen.

Vapor transfer technique

Diaphram
pressure

5.9.2 Wille Geotechnik Cell
A single-soil-specimen pressure plate apparatus was designed
and built by Wille Geotechnik in Gottingen, Germany. The
soil specimen is contained inside a metal ring for K 0 loading
conditions. Both water content changes and volume changes
can be measured provided the specimen does not shrink away
from the sides of the metal ring. Figure 5.84 shows the cell
placed in the hydraulic loading frame. Figure 5.85 shows
drying and wetting curve water contents measured on sand
using the Wille cell (Lins and Schanz, 2004). Volume changes
were also recorded and void ratio was calculated; however,
the sand showed small changes in void ratio, as shown in
Fig. 5.86. Figure 5.87 shows the computed degrees of sat-
uration as applied suctions were changed. The apparatus is
capable of measuring water content and void ratio changes
with applied matric suction and total stresses. These results
show that it is possible for a variety of stress paths to be
followed and in this way the entire constitutive surfaces for
water content and void ratio can be measured. The Wille cell
can be placed within a loading frame for the application of
vertical stresses.

RH control

Sample

A

B

C valve closed
during vapor transfer

RH control

Solution

Air pump

Electric
balance

(a) Barcelona cell used to apply total suction to a soil

Axis translation technique

5.9.3 Fredlund Pressure Plate Cell
(D.G. Fredlund, 2001)
The Fredlund cell shown in Fig. 5.88 was manufactured by
GCTS in Tempe, Arizona. The pressure plate cell accommo-
dates the measurement of water content and overall volume
change on a single soil specimen under various K 0 total
stress loading conditions (Pham et al., 2002). Desorption
SWCC can readily be measured. More time is required and
greater experimental care is needed when measuring the
adsorption SWCC curve. Soil suctions as high as 1500 kPa
can be applied. A small air pressure booster system can also
be purchased for the application of high air pressures.
The Fredlund SWCC device comes with interchangeable
high-air-entry disks. The device consists of a pressure cell
assembly and a pressure panel as shown in Fig. 5.89. The
pressure plate device can accommodate various sizes of
specimens ranging between 62 and 75mm in diameter. The
height of the specimen can be between 12 and 25 mm.

Diaphram
pressure

Sample

C

HAEV ceramic disk

Coarse metalic disk

Base plate

(b) Barcelona cell used to apply matric suction to a soil.

Figure 5.83 Barcelona K 0 pressure plate cell. (Courtesy of
CIMNE, Barcelona, Spain.)