In parallel with these investigations, extensive and detailed surveys
are required to establish the location and extent of potential sources of
construction materials in reasonable proximity to the site. The materials of
interest may range from low-permeability cohesive soils and glacial tills for
embankment cores through to sands and gravels suitable for shoulder fill
or as concrete aggregates. Crushed rock may also be obtainable from exca-
vations for underground works associated with the project.
Overall site viability is additionally subject to economic considera-
tions, notably site preparation and construction material costs. It may also
be influenced by seismicity, access development cost or other local con-
straints, including environmental and socio-political considerations.
In summary, dam site investigations require careful planning and the
investment of sufficient time and resources. Wherever possible, in situand
field test techniques should be employed to supplement laboratory testing
programmes. Proper and meticulous interpretation of geological and geo-
technical data demands the closest cooperation between the engineering
geologist, the geotechnical specialist and the dam engineer. Underinvestment
in reservoir site appraisal and in the investigation and assessment of the site
for a dam can have grave consequences, both technical and economic.
1.6.3 Geological and geotechnical investigations
Geological and geotechnical investigation of a dam site selected for
detailed evaluation is directed to determination of geological structure,
stratigraphy, faulting, foliation and jointing, and to establishing ground and
groundwater conditions adjacent to the dam site, including the abutments.
The general objectives of these and allied investigations are
(a) to determine engineering parameters which can reliably be used to
evaluate stability of the dam foundation and, on compressible founda-
tions, i.e. soils, to estimate probable settlement and deformation,
(b) the determination of seepage patterns and parameters enabling
assessment of the probable seepage regime, including quantities and
pressures, and
(c) to confirm the containment integrity of the reservoir basin and the
stability of its margins.
The relative importance of (a), (b) or (c) is dependent upon the site and
the type of dam proposed. A fourth general objective is
(d) confirmation of the nature, suitability and availability of natural con-
struction materials, including the determination of design parameters
for fill materials etc.
26 ELEMENTS OF DAM ENGINEERING
