SMALL DAMS

Chapter III
is highly useful when the origin of problems or abnormal behaviour must be
investigated several months or years after the work is finished. This recommendation
is just as valid for the smallest dams.
Methodology for geological work supervision
To meet this objective, the geologist must be involved in construction through periodic
visits, some of them scheduled according to works phases that require his assistance
(acceptance of excavations, etc.), and the rest on a regular basis to be determined
according to the characteristics of construction (dimension of the structures, geological
complexity, contractor's experience).
It is therefore important that the geologist be kept informed in good time of how the
work is progressing in order to be able to schedule his visits and avoid:
!" not being able to carry out the planned observations and acceptance;
!"delaying the works (works stoppage or filling in excavations, etc.), which is always
a difficulty and creates conflicts that usually have an adverse effect on the quality of
the work.
A non exhaustive list of the tasks to be accomplished during construction of a dam is
as follows:
!" Supervising excavation of all kinds (abutment contact, cut-off trench, surface stripping,
tunnels excavated in the rock, etc.):
- comparison with plans, decision to stop or continue the excavation (adapting
the level where the excavations are stopped to actual geological conditions);
- monitoring the stability of excavations, river banks and slopes (excavated or
backfilled), if necessary including the decision to reinforce (pinning unstable
boulders, gentler slopes, nailing or shoring up loose slopes, etc.).
!" Geological survey of excavations (abutment contact, cut-off trench, surface stripping,
ancillary concrete structures such as tunnels, spillway or intake tower): this is
generally done for structures of a certain size when the excavations are contractually
taken over as foreseen in the contract and can involve photography, sampling, plotting
crack patterns, and precise surveying of particular points visible in the excavations.
!" Geological survey of tunnels excavated in the rock (generally restricted to the
largest of the structures dealt with herein): representation of the nature of the terrains
and their structure (cracking, dip, schistosity, porosity) on a detailed drawing of the
tunnel's cross-section, indicating all of the hydrogeological elements (cavities, inflows
of water, leaks, etc.).
! " Supervision of sampling of construction materials for earthfill dams:
- comparison of the terrains actually encountered with plans and inspection
that borrow material is in compliance with the contract specifications;
- search for new borrow areas if necessary;
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