SMALL DAMS PETITS BARRAGES

Kind of reinforcement of the
dam slope
Coarse surface (stone packing,
armouring, vegetation cover)
Smooth surface
(asphalt-concrete,
concrete, pavement)
5.4.5 Camber
Table 5.6 – Height of wind waves
Camber (overbuild) of the crests of embankment dams is generally provided, in addition
to conventional freeboard allowances, to accommodate anticipated post-construction
settlements. Federal guidelines in the U.S. also recommend increasing freeboard in areas
that have high seismic activity to accommodate the possibility of permanent embankment
displacements and/or reservoir seiches during large earthquakes (ICODS, 1998). If the
reservoir rim is unstable, additional freeboard may also be provided for the possibility of
landslide-generated water waves and/or displacement of reservoir volume.
5.5 SOIL COMPACTION
Compaction is the most important factor in achieving a stable, durable and solid earth
embankment, which is resistant to the constant seepage of water through the soil as well as
having stable slopes. It is important to point out that many dams failed because of poor
compaction.
Compaction occurs when pressure is applied to the soil so that the individual soil grains
are pushed together as air is expelled. Compaction in the field is directed at reducing the
percentage voids to less than 5%. Compaction of soil to a certain standard (i.e. density and
water content) not only prevents excessive leakage and failure but also provides the basis for
the determination of other properties e.g. strength, permeability, settlement and elasticity. By
applying compaction to a specific standard a norm is set against which the properties are
known and the behaviour and safety of an embankment can be forecasted.
Stress/strain deformation characteristics of embankments are also important.
Embankments should under no condition develop low compressive stresses and excessive
shear forces as this can lead to failure.
5.5.1 Compaction Standards
Effective length of
wave run-up
in meters
Height of the wave run-up in m
For a design speed 72 km.h-1
1 : 3 1 : 2
100 0.33 0.42
200 0.43 0.54
300 0.50 0.64
100 0.42 0.53
200 0.54 0.67
300 0.62 0.80
Regardless of the type of compacting equipment or the degree of cohesion of the soil,
the effectiveness of the compaction procedure depends to a large extent on the moisture
content of the soil. This statement applies especially to almost nonplastic uniform fine-grained
soils.
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