SMALL DAMS

F ill dams
However, when the material is not very homogeneous, it is preferable that each layer
be compacted with an increasing number of passes, and successive measurements
be taken at the same place.
The optimal number of passes to reach the desired dry density must generally be
between 6 and 12, in order to achieve fill of sufficiently homogeneous compactness
and to optimise use of the machinery. The thickness of the layers will be increased or
reduced depending on whether the number of passes required is less than 6 or
greater than 12.
That thickness, after compacting, must nevertheless always be between 0.20 and 0.50
metre. It should be checked that the entire thickness of the layer is properly compacted.
Digging a trench is one way to observe the homogeneity of the compacted material.
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Equipment
There are three main categories of compactors:
!"pneumatic tyred rollers are suitable for compacting almost all soils, but the use of
heavy rollers means a risk of layers being foliated, while less heavy rollers may be
ineffective at greater depths;
!" tamping rollers, preferably self-propelled, are suitable for compacting fine soils;
!" smooth vibrating rollers, generally self-propelled, are preferably reserved for
granular soils (sand, dry gravel) and rock materials. They are very effective at depth
but not on the surface, at least for the first 2 to 5 centimetres.
As concerns excavation and transport of materials, the two most commonly used
methods are:
!" the motorscraper;
!"the mechanical shovel along with trucks or dumpers, which helps in mixing several
different layers and is most suitable when the borrow area is far from the dam or has
a pronounced relief.
WORKS SUPERVISION
After drawing the conclusions from the test section, the objective is to build, under the
best possible conditions, a structure that will be used for several decades, with the
least possible maintenance.
General philosophy of works supervision
Whatever the quality of the geotechnical studies done on the project, they are always
limited in scope, both as concerns the investigations on the foundation and those in
the borrow areas.
Construction will therefore often reveal situations that were not foreseen during the
studies and to which the works must adapt very quickly.