Geoscience Reference
In-Depth Information
pitch emulsion (asphalt) is the best. However, with the high cost and lack of source,
it cannot be extended on a large scale. Other materials tested are in the following
models:
•
In Taklimakan Desert, Chinese oil gas farms made trials of some man-made
materials to cover the moving sand surface around oil gas facilities, along the
expressway and tent settlements. These materials include: used plastics, poly-
fiber, nylon and acrylic wire netting, oil based products and straw matrix.
•
In Dunhuang, acrylic netting and nylon cloths are used to cover sand surfaces to
protect the ancient Buddhist Grottoes of Magao.
•
In Zhongwei County, Ningxia Hui Autonomous Region, some chemicals were
adapted to fix shifting sand surfaces. The chemicals include: asphalt emul-
sion, OT-asphalt, ABS asphalt emulsion, OP-asphalt emulsion, Polyacylamide,
Polyvinyl alcohol, Polyvinyl acetate, Hydrolytical polyacrylonitrite, and sodium
silicate.
4
Standing Sand Barriers
If surface sand barriers affect one prerequisite of sand movement, standing sand
barrier affect the other, namely wind. Wind velocity is reduced when any barriers
obstructs the wind and some of the sand carried by the wind will heap up around the
barriers when the wind velocity is reduced. The sand carrying capacity of the sand-
driving wind is reduced by a big margin. According to studies on the structures of
the sand-driving wind, 80-90 % of the total sand capacity of the sand-driving wind
is found at the height of 20-30 cm above the ground and within this height of 20-
30 cm, most of the sand is carried under a height of 10 cm above the ground. For this
reason, if the standing barriers set up in the path of the sand-driving wind maintains
a height of between 30-50 and 100 cm, most of the blown sand can be controlled.
We can let the sand be carried by the sand-driving wind to heap up at the designated
places through the setting-up of standing barriers. The dropped sand around the
barriers will remain there because the wind velocity is reduced both behind and in
front of the barriers, and the threat of the sand to any object can be eliminated by
such standing sand barriers.
The weak wind areas formed on the leeward side and on part of the windward
side of the sand barrier can allow the sand carried by the sand-driving wind to
drop down and become fixed. Plantation on the bare surface of the sand dunes can
be guaranteed because the standing sand barriers eliminate the sand-driving wind.
Standing sand barriers, which are 50-100 cm high, are called high standing sand
barriers. Standing sand barriers whose height is between 20 and 30 cm are called
low standing sand barriers. Materials used for standing sand barriers, in general,
are the following: straws or stalks of crops, tree branches, clay, and many other
materials. Sand barriers made of any of these materials can reduce the wind velocity
and heap up or stabilize the sand around the sand barriers. Standing sand barriers can
Search WWH ::
Custom Search