Environmental Engineering Reference
In-Depth Information
Figure 15.29.
Mangrove Creek Dam (MacKenzie and McDonald, 1985, reproduced with permission of
ASCE).
but may not be free draining. Rocks which are likely to do this are sandstones, siltstones,
shale, schists and phyllites.
If this is the case, CFRD can still be used but must be zoned to provide drainage layers
behind the face slab and on the foundation.
Mangrove Creek Dam is an example of this design, as discussed in detail in MacKenzie
and McDonald (1985).
Figure 15.29 shows the zoning.
Other examples are Kangaroo Creek and Little Para Dams (Good et al., 1985) and
Salvajina Dam (Sierra et al., 1985). Zoning for Salvajina Dam is shown in Figure 15.7 . In
this case the rockfill zones are compacted gravel which have significant silt content, and
the drainage layer 2A is provided to ensure dam leakage will not result in build up of pore
pressure in the dam.
It is not uncommon to zone the rockfill to ensure that the most free draining material is
downstream of Zone 2E and on the base of the dam.
15.5.2
Dams on poor foundation
Concrete face rockfill dams have been successfully constructed on foundations which
have weathered seams or clay filled joints, which were potentially erodible under the high
gradients which occur under the face slab.
In these circumstances, it has been necessary to prevent erosion by lengthening the seepage
path and by providing filters into which the under-seepage emerges in a controlled manner.
An example is Winneke Dam. The deeply weathered siltstone rock precluded economic
placement of the plinths on fresh rock and the slab was founded at a level where weath-
ered rock contained infilled joints and crushed seams, some of which were dispersive clays
( Figure 15.30 ).
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