22
@ U S T . H K
Tap
root
Plate-
shaped
root
Heart-
shaped
root
A novel model root water uptake system
and three types of root architecture for
centrifuge model tests.
Artificial Model Roots
NEW MODEL ROOT SYSTEM
Root hairs
extract moisture
from soil
Transpiration
Water flows upward
Connected to
controllable vacuum source
Balance
IDEALIZATION
INCREASING WATER POTENTIAL
High air-entry valve
(AEV) porous filter
saturated with de-aired
water, preventing
unsaturated soil
particles from entering
Hollow tube
completely filled
with de-aired water
Vacuum chamber
Getting to the Root of
Unsaturated Soils
Over the past two decades, Prof
Charles Ng has taken up the challenge
posed by unsaturated soils. He has
advanced fundamental knowledge
and practice related to slope stability
and maintenance, as well as debris
flows, a type of fast-moving landslide.
In Hong Kong alone, there are tens
of thousands of man-made and
natural slopes. Recognizing early that
these geomaterials needed further
exploration, Prof Ng established the
unsaturated soil research group at
HKUST in 1995 and started the first
postgraduate courses on unsaturated
soils in Asia the following year.
They have gone on to develop a
series of theoretical state-dependent
elastoplastic
frameworks
for
unsaturated soils, which have become
the theoretical basis for experimental
and further theoretical studies by
researchers globally. Unlike previous
ON SAFER AND SUSTAINABLE GROUND
The University’s geotechnical researchers are global leaders in
the theory and engineering of unsaturated soil mechanics, slope stability,
mitigation of landslide risk, and risk assessment of multi-hazards
While residing in our rapidly expanding
cities is often likened to living in a
concrete jungle, few recognize that
99.99%
of
man-made
structures
are actually supported by natural
geomaterials, such as soil and rocks.
Unsaturated soils, covering most of the
Earth’s land surface, are one such type of
geomaterial and, like other geomaterials,
their behavior and properties are highly
complex, since they are path-dependent
(resembling our upbringing and history),
stress-dependent, and strain-dependent.
These soils are also prone to external
loads, such as earthquakes, rainfall, and
changes in temperature and humidity.
Such loads can cause the soils to expand
or contract and potentially collapse,
making them hazardous to the natural
and man-made structures they support.
Understanding these intricate soils is
therefore challenging but essential if we
are to achieve sustainable development
and enhance the mitigation of natural
and human-induced disasters.
The roots of plants grown on natural and man-made slopes offer an elegant solution to stabilize slopes. They help to provide both mechanical anchoring as
well as soil suction via transpiration to reduce water infiltration, and increase shear resistance to potential failure.
Soils are highly complex and
varied, just like people,
and offer a cornucopia of
knowledge for someone
with a curious mind
PROF CHARLES WW NG
CLP Holdings Professor of Sustainability,
Associate Vice-President for Research
and Graduate Studies,
President of the International Society for
Soil Mechanics and Geotechnical Engineering
Green Slope Engineering
TRANSPIRATION
DIVERSE
VEGETATION
Unsaturated
zone
Saturated
zone
Vadose zone
GROUND
WATER TABLE
POTENTIAL
DEEP-SEATED
FAILURE
POTENTIAL
SHALLOW
FAILURE
