Environmental Engineering Reference
In-Depth Information
Solution No. 5:
New instrumentation such as the direct,
high-suction tensiometer and the indirect thermal con-
ductivity suction sensor has provided new measurement
techniques for the laboratory and the field. These devices
allow suctions to be measured over a considerable range
of matric suctions. The null-type, axis translation tech-
nique remains a laboratory reference procedure for the
measurement of matric suction.
Challenge No. 6:
New technologies and engineering
protocols such as those proposed for unsaturated
soil mechanics are sometimes difficult to incorporate
into engineering practice. The implementation of
unsaturated soil mechanics into engineering practice
has proven to be a challenge.
Solution No. 6:
Educational materials, visualization
systems, computer software, and research conferences
have greatly assisted in effective technology transfer.
It has been possible to demonstrate through teaching,
software demonstrations, and research conferences
that the concepts of unsaturated soil behavior can be
implemented in engineering practice. Information on
unsaturated soil mechanics is also being incorporated
into the undergraduate and graduate curricula at uni-
versities. Protocols for engineering practice are being
developed for all application areas of geotechnical
engineering.
Changes are necessary in geotechnical engineering prac-
tice in order for unsaturated soil mechanics to be imple-
mented in a routine manner. Each challenge in unsaturated
soil mechanics has been met with a definitive and practi-
cal solution. A significant paradigm shift has been required
with regard to the determination of unsaturated soil property
functions (Houston, 2002). New approaches that have been
developed have provided cost-effective procedures for the
determination of unsaturated soil property functions for all
classes of problems (Fredlund, 2002a).
1.1.5 Laboratory and Field Visualization of Degree
of Saturation
Climatic conditions around the world range from very
humid to dry. Climatic classification is based on the
average annual net moisture flux at the ground surface (i.e.,
precipitation minus potential evaporation; Thornthwaite,
1948). The ground surface climate is an important factor that
controls the depth to the groundwater table and therefore the
thickness of the unsaturated soil zone (Fig. 1.2).
The zone between the ground surface and the water table
is referred to as the unsaturated soil zone. This is somewhat
of a misnomer since the capillary fringe immediately above
the water table is essentially saturated. A more correct term
for the entire zone above the water table is the “vadose
zone” (Bouver, 1978). However, the entire zone subjected
Precipitation
Evaporation
Regional
discharged
area
Local
discharged
area
Transpiration
Regional
discharged
area
Unsaturated
zone
DRY ZONE
- discontinuous water phase
- air filling most voids
TWO-PHASE ZONE
- continuous water
- continuous air
CAPILLARY ZONE
- water filling most voids
- air phase discontinuous
GROUNDWATER TABLE
- water filling the voids
- air in a dissolved state
Figure 1.2
Subdivisions of unsaturated soil zone (vadose zone) on local and regional basis.
Search WWH ::
Custom Search