Hydro-Mechanical Properties of an Unsaturated Frictional Material

2.3. HYDRAULIC FUNCTIONS 33
is applied to the specimen. Klute (1986) provides description of steady-state methods
for measuring unsaturated hydraulic conductivity.
The steady state centrifugation method is a laboratory method. It uses a spinning
centrifuge, which establishes fast steady-state fluid flow trough a soil. The unsatu-
rated hydraulic conductivity is calculated by measuring the steady-state flow under the
elevated gravitational gradient (Nimmo et al. 1987, Nimmo & Akstin 1988).
The crust method is a steady state test to measure the unsaturated hydraulic conduc-
tivity in the field (Hillel & Gardner 1970). Tension infiltrometer, which measures the
infiltration rate under carefully controlled suctions also can be used in the field. Differ-
ent methods for calculating the unsaturated hydraulic conductivity based on these data
were proposed by Elrick et al. (1987), Ankeny et al. (1991), Reynolds & Elrick (1991),
Logsdon & Jaynes (1993).
- Direct Method performed under Transient State Condition:
Under transient state conditions, the specimen is subjected to continuous unsaturated
flow conditions and measurements are carried out while the specimen comes to equi-
librium. Transient state methods are for instance the horizontal infiltration method,
the outflow methods and the instantaneous profile method. Transient state test was
performed by Klute (1965) in a horizontal column. The column consisted of several
segments. The saturation of the dry soil in the column was stepwise increased from
S = 0 to S = 1, by introducing water from one end of the column. Thus a hydraulic
gradient is imposed to the soil. After some time the inflow of water is stopped, the col-
umn is disassembled into its segments and the water content is determined. Horizontal
infiltration tests have been also explored by Jackson (1964), Rose (1968), Clothier et al.
(1983).
The instantaneous profile method is applicable in the laboratory and in the field and
was first proposed by Richards & Weeks (1953). This method uses transient profiles of
water content and suction to calculate the unsaturated hydraulic conductivity. Drainage
process was induced by gravity (Watson 1966), by withdrawing fluid from the specimen
via applied suction (Richards & Weeks 1953), by applying flow rate to the specimen
(Overman & West 1972) or by evaporation (Wind 1966, van Grinsven et al. 1985,
Wendroth et al. 1993, Meerdink et al. 1996). Imbibition was performed by adding water
to the soil specimen (Hamilton et al. 1981, Daniel 1982, Meerdink et al. 1996). Most
recent approaches include both measurement of suction and water content (Malicki et al.
1992, Meerdink et al. 1996). Example of permeameter for conducting instantaneous
profile method is suggested in Meerdink et al. (1996). When suction as well as water
content measurements are available then the unsaturated hydraulic conductivity and
also the soil-water characteristic curve can be determined. Laboratory instantaneous
profile method is performed in a horizontal or vertical column. During the testing