Concrete face rockfill dams - Geotechnical Engineering of Dams - page 648

Figure 15.40. Scotts Peak dam (courtesy of HEC Tasmania).

There was also a rapid increase in the rate of settlement in the short period before gravels
were dumped over the damaged area of the face.
Xingo Dam in Brazil (140 m high) has been built in several stages. Horizontal cracking
of the face slab has occurred near the stage interface indicating differential deformation in
the embankment between the materials placed in the different stages.
At Guohou in China failure is attributed to a crack that opened at the joint between the
face slab and the crest wall following deformation of the zoned gravel embankment
(Chen, 1993). However the detailing and construction of this joint was poor.
These features indicate that in the case of the higher CFRD embankments it is impor-
tant to limit the potential for differential deformation of the rockfill, particularly in the
higher sections of the dam, and to provide high permeability zones to discharge the leak-
age safely.

15.7 OBSERVED LEAKAGE OF CFRD

15.7.1 Modern CFRD

Table 15.12 shows leakages which have been recorded on first filling and during opera-
tion for a selection of dams for which data is available.
The following case studies demonstrate some important features of dams which have
experienced relatively large leakage:

(a) Alto Anchicaya Dam - High leakage rates measured during first filling ( 1800 l/s in

the right abutment). Flooding from a creek on the right abutment during construction
caused some wash-out of filter material beneath the perimetral joint and may have
been a contributing factor to the excessive leakage. A single rubber waterstop was
adopted in the construction of Alto Anchicaya. Inspections of the perimetric joint dur-
ing remedial treatment revealed that while the rubber waterstop was intact it was rel-
atively loose and concrete had not penetrated under the waterstop very well during
construction (Regalado et al., 1982).
Remedial treatment included filling the joints with a mastic compound and a sand-
asphalt and/or compacted clay cover. Long-term leakage rates stablised after remedial
works to a rate of approximately 130 l/s.
(b) Aguamilpa Dam - Leakage rates measured during first filling were considered rela-
tively normal until the water level reached a depth of approximately 173 metres, at which
point the rate rose to approximately 260 l/s. Several horizontal and diagonal cracks were
found in the face slab at a water depth of approximately 150 metres (Gomez et al., 1999).