Geology Reference
In-Depth Information
• appearance of leaks in the reservoir, which can have negative effects
on the exploitation of the structure and cause various impacts, on
sometimes distant sites;
• creation of water channels under the dam's foundations, directly
jeopardizing its stability;
• modifi cations in the equilibrium conditions on the shores of the
reservoir, which can infl uence the safety of the dam and the downstream
population.
The last two cases can lead to real disasters, as shown by the destructive
events touching a number of countries:
• in 1802: Puentes (Spain) gravity dam failure: 680 victims;
• in 1889: Johnstown, Pennsylvania (USA) earthen dam failure: 2,200
victims;
• in 1895: Bouzey, Vosges (France) gravity dam failure: 86 victims;
• in 1911: Austin, Pennsylvania (USA) concrete gravity dam failure: over
100 victims;
• in 1923: Gleno (Italy) multiple-arch dam failure: 600 victims;
• in 1928: Saint-Francis, California (USA) masonry gravity dam failure:
450 victims;
• in 1959: Malpasset, Var (France) arch dam failure: 423 victims;
• in 1963: Vajont (Italy), collapse of one bank of the reservoir: 1,700
victims.
The preliminary study and subsequent construction of a dam and its
reservoir therefore require a very serious analysis and, particularly, in-depth
examination of the geologic structure and of the hydrogeologic behavior
of the relevant units.
2 DAM STABILITY
The rise in water level behind a dam increases the static pressure of the
aquifer partially or totally saturating the units supporting the project and
its banks, increasing, in particular, the hydraulic gradient between upstream
and downstream, especially in the case of large dams. This state facilitates
the infi ltration of water underneath the dam's foundations or around its
supports.
Such forced flow can cause the regressive erosion of alterable
formations, the washing out of fi ne-grained particles and the creation of
internal erosion, or even the appearance of pressure from below, so many
situations that can be very dangerous for the stability of the dam and the
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