material processing and transportation costs, availability of plant and trained
labour, ease of river diversion, risk of flood inundation during construction
and construction period relative to the desired project commissioning date.
Design features of dams which can have major implications with
regard to construction programming and costs include
- cut-offs,
- spillway systems, including channels and stilling basins,
- internal drainage systems,
- internal culverts, galleries, etc.,
- foundation preparation, including excavation and grouting, etc.,
- construction details, e.g. transitions or filters in embankments or con-
traction joint details in concrete dams, - gates, valves and bottom outlet works, and
- river diversion works.
1.7 Loads on dams1.7.1 GeneralThe structural integrity of a dam must be maintained across the range of
circumstances or events likely to arise in service. The design is therefore
determined through consideration of the corresponding spectrum of
loading conditions. In all foreseeable circumstances the stability of the
dam and foundation must be ensured, with stresses contained at accept-
able levels and watertight integrity essentially unimpaired.
Dams display a sophistication in their structural response which
stands in sharp contrast to their apparent simplicity of structural concept
and form. They are asymmetrical and three-dimensional structures, con-
structed from materials with complex physical properties and founded
upon non-uniform and anisotropic natural formations. This is reflected in
the interaction of the dam with its foundation and in the complex struc-
tural response of both when subjected to fluctuations in major loads and to
the effects of progressive saturation. In comparison with most other engin-
eering structures, dams are also required to function at or near their speci-
fied design load for a high proportion of their service life as noted earlier.
Certain loads are accurately predeterminate with regard to their dis-
tribution, magnitude and mode of action. Obvious examples are external
water loads and structure self-weight. Other major loads, some equally
important, are less reliably predeterminate and may also be time depend-
ent. Examples are provided by internal seepage pressures, by the load
redistribution effected through foundation deformations or, in concrete
dams, by thermal effects associated with cement hydration etc.