Page 39 - Water and DSİ

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CHAPTER III - HYDROELECTRIC ENERGY
3.5.2.3. Roller Compacted Hardfill Dams
The impermeability of upstream face of the Hardfill dam is to be ensured by PVC membranes
installed on inside of the precast concrete panels acting as cast when hardfill is filled and protects
PVC membranes. Drains installed horizontal and vertical reduces inner water pressure of the dam
body and ensures safety for earthquake.
Likewise RCC dams, hardfill dam embankments are constructed in similar way. Unlike RCC dams,
the upstream and downstream faces of hardfill dams embankments are slanting. Hence, tensile
stress does not emerge. Hence, amount of agglomerant material (binding cementing) is much
lower that of RCC dams (Lower than (100 kg/m³). Amount of cement could be 40-50 kg/m³ and
amount of flyash could be 30-50 kg/m³. (e.g., 40 kg/m³ cement, 30 kg/m³ flyash). Hereby, hardfill
dam embankments may be constructed upon the lower bearing quality foundations than those of
RCC. Harfill dams may be consructed on rock foundation elasticity module of which is equal an
over 1 Gpa. for Fine aggregate up to 40-45% into one m³ of the mixture of RCC might be
acceptable.
3.5.3. Concrete Dams
3.5.3.1. Concrete Gravity Dams
The whole concrete embankment body is to be impervious. Concrete Gravity Dams have often
perpendicular triangle cross-section mass structure. Concrete Gravity Dam resists shear and
turnover effect arising from all external loads by means of its gravitation. It necessitates high
resisting concrete. Hereby, good quality gronometric cement and sand-gravel (or crushed stone).
Concrete Gravity Dams are often constructed on narrow gorges and on strong rock foundations.
Spillway, sluiceway, intake structures are generally designed on the dam body.
Construction of high agglomerated quality concrete mixture entails much more intricate
construction process. Maximum construction temperature becomes very important during the
concrete construction. Supplying and cooling of aggregate entails additional painstaking process.
Concrete Gravity Dams with filled body are designed by juxtaposing trapezoidal concrete blocks
having from 10 to 20 m width (so as to prevent thermal cracks). Generally, the notched faces of
concrete blocks forming the joints are constructed in the way in which two faces clutches one
another. Dam body and rock foundation are to be sound enough to resist shear and turnover
effects and ground tensions.
3.5.3.2. Concrete
Arch Dams
They are constructed on canyon, foundation of which and banks of which are strong rock. Arch
dams transmit much of the load emerging from upstream direction to banks thanks to arch form
of the embankment. Albeit the embankment is built in discrete blocks, the embankment functions
as monolithic bloc once the joints are filled by injections. Arch dams can be designed as gravity
arch dams and double curvature arch dams.
3.5.3.2.1. Concrete
Gravity Arch Dams
The cross-sections of gravity arch dam and gravity concrete dam are similar. But, Gravity arc dam
is different in that the embankment axis is curvature and upstream face is more perpendicular that
of gravity concrete dam.
3.5.3.2.2.
Double curvature Arch Dams
Double curvature dams have both horizontal and vertical curvatures.