- As a corollary to 2, all concrete dams can accommodate a crest spill-
way, if necessary over their entire length, provided that steps are
taken to control downstream erosion and possible undermining of
the dam. The cost of a separate spillway and channel are therefore
avoided. - Outlet pipework, valves and other ancillary works are readily and
safely housed in chambers or galleries within the dam. - The inherent ability to withstand seismic disturbance without cata-
strophic collapse is generally high. - The cupola or double-curvature arch dam is an extremely strong and
efficient structure, given a narrow valley with competent abutments.
Type-specific characteristics are largely determined through the dif-
fering structural modus operandiassociated with variants of the concrete
dam. In the case of gravity and buttress dams, for example, the dominant
structural response is in terms of vertical cantilever action. The reduced
downstream contact area of the buttress dam imposes significantly higher
local foundation stresses than for the equivalent gravity structure. It is
therefore a characteristic of the former to be more demanding in terms of
the quality required of the underlying rock foundation.
The structural behaviour of the more sophisticated arch and cupola
variants of the concrete dam is predominantly arch action, with vertical
cantilever action secondary. Such dams are totally dependent upon
the integrity of the rock abutments and their ability to withstand arch
thrust without excessive yielding. It is consequently characteristic of
arch and cupola dams that consideration of their suitability is confined to
a minority of sites in relatively narrow steep-sided valleys or gorges,
i.e. to sites with a width:height ratio at the dam crest level generally not
exceeding 4–5.
A comparison of the general characteristics of concrete dams with
those of the embankment dam suggests the following inherent disadvant-
ages for the former.
- Concrete dams are relatively demanding with respect to foundation
conditions, requiring sound and stable rock. - Concrete dams require processed natural materials of suitable
quality and quantity for aggregate, and the importation to site and
storage of bulk cement and other materials. - Traditional mass concrete construction is relatively slow, being
labour intensive and discontinuous, and requires certain skills, e.g.
for formwork, concreting, etc. - Completed unit costs for mass concrete, i.e. cost per cubic metre, are
very much higher than for embankment fills, typically by an order of
magnitude or more. This is seldom counterbalanced by the much
lower volumes of concrete required in a dam of given height.