The relative disadvantages of the embankment dam are few. The
most important include an inherently greater susceptibility to damage or
destruction by overtopping, with a consequent need to ensure adequate
flood relief and a separate spillway, and vulnerability to concealed leakage
and internal erosion in dam or foundation. Examples of alternative types
of embankment dam are illustrated and described in Thomas (1976),
Golzé (1977) and Fell, MacGregor and Stapledon (1992).
1.4 Concrete dam types and characteristics
Rubble masonry or random masonry was successfully employed for many
early dams. In the latter half of the 19th century masonry was used for
high dams constructed in accordance with the first rational design criteria.
Cyclopean masonry (i.e. stones of up to c.10 t mass individually bedded in
a dry mortar) was generally used, with a dressed masonry outer facing for
durability and appearance (Binnie, 1987b).
Mass concrete, initially without the formed transverse contraction
joints shown on Fig. 1.4(a), began to displace masonry for the construction
of large non-embankment dams from about 1900 for economic reasons
and also for ease of construction for more complex dam profiles, e.g. the
arch. Early mass concrete commonly employed large stone ‘displacers’ (cf.
cyclopean masonry). From about 1950 mass concrete increasingly incorpo-
rated bulk mineral additives, e.g. slags or pulverized fuel ash (PFA), in
attempts to reduce thermal problems and cracking and to contain escalat-
ing costs.
The principal variants of the modern concrete dam are defined below.
- Gravity dams.A concrete gravity dam is entirely dependent upon its
own mass for stability. The gravity profile is essentially triangular,
with the outline geometry indicated on Fig. 1.4(a), to ensure stability
and to avoid overstressing of the dam or its foundation. Some gravity
dams are gently curved in plan for aesthetic or other reasons, and
without placing any reliance upon arch action for stability. Where a
limited degree of arch action is deliberately introduced in design,
allowing a rather slimmer profile, the term arched or arch-gravity
dam may be employed.
- Buttress dams.In structural concept the buttress dam consists of a
continuous upstream face supported at regular intervals by down-
stream buttresses. The solid head or massive buttress dam, as illus-
trated by Figs 1.4(b) and 1.4(c), is the most prominent modern
variant of the type, and may be considered for conceptual purposes
as a lightened version of the gravity dam.
- Arch dams.The arch dam has a considerable upstream curvature.
Structurally it functions primarily as a horizontal arch, transmitting
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