Environmental Engineering Reference
In-Depth Information
Figure 15.31.
Plinth and gallery, Khao Laem Dam (Watakeekul et al., 1985, reproduced with permis-
sion of ASCE).
and the weathered rock between it and the downstream toe, was then covered by 2A and
2B type filter materials.
At Mohale Dam (Gratwick et al., 2000) two significant geological lineaments cross the
damsite and were assessed to have potential for movement. Treatment included the excava-
tion of a slot to provide a concrete “socle” 15 m wide and 2 m deep below the toe-slab, a grout
curtain directed through the lineament and a grouting gallery extending from the downstream
side of the embankment to the toe-slab area near the lineament. Both the socle and the toe-
slab incorporate movement joints composed of 20 mm of compressible material and a PVC
waterstop. Upstream of the toe-slab a blanket of earthfill is placed for a distance of 70 m and
downstream protection is provided by a geotextile and reverse filters of 2D and 2E material.
Another example of special foundation treatment is described by Sierra et al. (1985) for
Salvajina Dam (
Fig 15.25
). In this case, the foundation was in part founded on residual
soil and wide concrete slabs were added upstream of the plinth and filters downstream.
When gravelly alluvium or glacial soils are present in the river bed, these can commonly
be left in place except for the first 0.3 H to 0.5 H downstream of the plinth. This is
dependent on confirmation that the gravels are of adequately high modulus and strength.
Potentially liquefiable gravels must be removed or densified.
15.5.3
Plinth gallery
The Khao Laem Dam, which was constructed on deeply weathered and in part karst foun-
dations, incorporated a permanent gallery over the plinth of the dam. Details are shown
in Figure 15.31.
The value of the gallery, as a means of access for remedial work, was shown when leak-
age developed through the perimetric joint. The leak was reduced by grouting from the
gallery, as described in Watakeekul et al. (1987).
Moreno (1987) describes the incorporation of a grout and drainage gallery in a 190 m
high CFRD, in a highly seismic area.
Figure 15.32
shows the gallery. Grouting from the
gallery assisted in meeting construction schedules.
15.5.4
Earthfill cover over the face slab
ICOLD (1989a), in their drawing showing typical design features of modern CFRDs (repro-
duced in
Figure 15.2
)
, show earthfill and random fill placed over the lower part of the plinth
(Zones 1A and 1B).
