SMALL DAMS

G eological and geotechnical studies
Final report
The final report is drafted after all the preceding stages have been completed and
includes:
!" a summary of all the geological studies done since the beginning;
!" the geotechnical summary mentioned above (preliminary geotechnical study);
!"definition of investigations for the tender design stage (core sampling, undisturbed
or remoulded samples, geophysical tests, geotechnical tests in a laboratory and in
situ, etc.);
!" supporting arguments for the type of dam recommended as the most suitable for
the site;
!" a preliminary sketch of the dam (zoning, slopes, cutoff trench excavations, etc.)
and an opinion on foundation treatment and if necessary treatment of the reservoir
basin.
GEOLOGICAL AND GEOTECHNICAL STUDIES IN THE TENDER DESIGN STAGE
For most small dams, this phase is combined with the preliminary design phase.
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Objective
Except in special cases, geological aspects are familiar at this point, and only extremely
localised site investigations will generally be necessary (in particular on foundations
of ancillary works such as the spillway, outlet tunnels, diversion tunnels, inspection
adits, intake tower, secondary dams if they were not considered in the preliminary
design).
However, if there is any significant change in the dam layout (or just the axis of the
watertight system) since the preliminary design site investigations, new core sampling
and water tests will be necessary on the new layout.
On the other hand, in this stage of study most of the geotechnical studies proper (soil
and rock mechanics according to the case) are necessary:
!" taking samples in numbers suited to the size of the dam and the conditions
encountered (geological complexity and variability of the soils), in the foundation
and in the planned borrow areas;
!"laboratory tests (with a schedule tailored to give good knowledge of the foundation
for the structures and the borrow areas). Their purpose is to give the designer the
necessary elements for tender design of the dam and to enable recommendations to
be made on geological and geotechnical aspects during the works and later monitoring
of the dam throughout its life. In France this stage of study for dams 20 metres
high or higher corresponds to the final brief that must be submitted to the Permanent
Technical Committee on Dams.