3301
Deformation safety of high concrete face rockfill dams
Calculs en déformations de la sécurité des grands barrages en rochement à masque amont en
béton
Li N.
Nanjing Hydraulic Research Institute, Nanjing 210029
Wang J.
China Hydro Northwest Investigation Design & Research Institute, Xian 710065, China
Mi Z.
Nanjing Hydraulic Research Institute, Nanjing 210029, China
Li D.
Nanjing Hydraulic Research Institute, Nanjing 210029, China
ABSTRACT
Based on the analysis of the mechanism of serious damages of high concrete face rockfill dams (CFRDs), it is indicated that the
causes of the cracking of cushion layer, the structural cracking and squeezed ruptures of concrete face slab are as follows: the
deformations of the dam different zones are not coordinated and the deformations of the concrete face slabs are not coordinated
synchronously with those of the dam body. The basis of empirical design that the water load on the concrete face enters the
foundation upstream from the dam axis is not correct. Therefore the empirical design concept of CFRDs should be changed. The
deformation safety is necessary for high CFRDs besides the stability safety and seepage safety for earth-rockfill dams. A new
deformation coordination concept and the deformation safety design of high CFRDs including deformation coordination standards,
judgment criteria and calculation methods are put forward. The deformation coordination design method for replacing the empirical
design concept is shown to be important for high CFRDs through the application of Bakun Dam.
RÉSUMÉ
Dans l’analyse des problèmes de stabilité des barrages en enrochements à parement amont en béton de grande hauteur (CFRD), il a
été remarqué que la cause de la fissuration du lit et du masque est le contraste de déformabilité entre les différentes zones constituant
le barrage (massif et parement amont). La conception basée sur l’expérience considérant que la chargement dû à l’eau agissant sur le
masque amont pénètre la fondation amont est incorrecte, et un changement dans le dimensionnement empirique des CFRDs devrait
être envisagé. Il est aussi nécessaire d’assurer un calcul de stabilité en déformations en plus des calculs à la rupture et vis-à-vis des
écoulements. Une nouvelle conception intégrant la compatibilité des déformations dans les analyses de stabilité des grands barrages
en enrochements à masque amont en béton est établie à partir de normes de distinction et des méthodes de calcul à travers une
application au projet de barrage de Bakun qui confirme l’intérêt de cette nouvelle approche par rapport à celles basées sur
l’expérience.
KEY WORDs:CFRD, deformation safety, empirical design,deformation coordination, standard,judgment criterion.
1 INTRODUCTION
It takes only 46 years there are more than 500 concrete face
rockfill dams(CFRDs) have been completed or under
construction in the world. The safety and economic condition of
CFRD are so good that CFRD has become the best dam type
with the most competitive ability usually. But the design of the
CFRD is empirical and is based on experience and precedent.
Some serious damages as follows have happened at several high
CFRDs since 1990’s. Some cracks of cushion zone happened at
Tianshengqiao No.1 Dam (178m high) and Xingo Dam(140m
high). The top of concrete face slabs separated mostly from
cushion layer and then more than 5000 cracks of concrete face
slab occurred at Tianshengqiao No.1 Dam. A lot of cracks of
concrete face slabs occurred then the seepage discharge reached
1700 L/s at Aguamilpa Dam(187m high). The serious cracks,
squeezed ruptures and horizontal overlaps of concrete face slabs
occurred at Campos Novos Dam(202m high), Barra Grande
Dam(185m high)and Mohale Dam(145m high) then the seepage
discharge increased an range from 600L/s to 1300L/s. The
crack and squeezed rupture of concrete face slab occurred also
at Tianshengqiao No.1 Dam and Shuibuya Dam(233m high).
The reason of cracking of cushion zone, separating of face
slab top from cushion layer, and cracking of concrete face slab
is that the deformation of dam different zones are not
coordinated and the deformation of concrete face slab are not
coordinated synchronously with the deformation of dam body.
The modulus of deformation of main rockfill zone (upstream
rockfill zone) is higher than that of downstream rockfill zone.
The deformation of dam body is much larger than the
deformation of concrete face slab. If the difference of
deformation between dam body and concrete face slab was
large enough to exceed the limit, the top of face slab would
separate from cushion layer and then cracks of face slab would
occur. The direction of the deformation of dam body faces the
center of the valley and at this time the friction force facing the
center of the valley occurs between concrete face slabs and
cushion layer. If the compressive stress at the central area of
concrete face slab exceeded the compressive strength limit of
concrete that the squeezed ruptures, cracks and horizontal
overlaps would occur. Therefore the deformation safety should
be satisfied necessarily besides the stability safety and seepage
safety for high CFRDs.
2 CONNOTATION OF DEFORMATION SAFETY OF HIGH
CFRD
The deformation safety of high CFRD includes the
deformation coordination of different zones of dam body and
the deformation coordination synchronously between the
