Geology Reference
In-Depth Information
For temporary works, corrugated steel sheets are generally driven,
vibrated or pushed into soil prior to deep excavation, with each sheet
linking to its neighbour. As the excavation proceeds, sheets are usually
braced by a system of struts and waling beams, although they may also
rely on depth of embedment. Diaphragm walls formed by concreting
deep trenches excavated under bentonite mud are also used as part of
temporary works and then may be incorporated in the permanent
structure. Permanent retaining structures are often created using piles.
Alternatively, where the ground can be anticipated to stand steeply,
temporarily during construction, the full slope is cut back and then a
wall of concrete constructed at some short distance in front. The space
between the wall and the natural ground is back
lledwith granular free-
draining material, often with geotextile material at the interface, feeding
water down to a drain
(Figure 6.29)
. Drainage is very important if the
retaining wall is not going to act as a dam. Gabionstructures are made
from galvanised steel or, rarely, plastic baskets, back
lled with rock.
The main advantages are that they are free-draining, can be landscaped,
and they can be made cheaply on site using locally derived rock to
ll
locally woven baskets. They are therefore very suitable for forming
retaining structures or barriers in remote locations (Fookes
et al
.,
1985). De
ection structures and barriers are commonly used to divert
or retain channelised debris
flows away from buildings or roads.
Whatever the engineering solutions adopted, slopes should be
examined periodically for signs of distress and for maintenance
such as cleaning out of drainage channels. The requirement for
inspection, testing and possible remediation works, should be built
into the design of any new slope, with careful consideration for
how this is to be achieved. In Hong Kong, the current practice is
