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18-12-2010, 02:50 PM
dams_ce242.ppt (Size: 1.37 MB / Downloads: 542)
Presented By:ABHINAV ANKUR
Dam is a solid barrier constructed at a suitable location across a river valley to store flowing water.
Storage of water is utilized for following objectives:
Water for domestic consumption
Drought and flood control
For navigational facilities
Other additional utilization is to develop fisheries
TYPES OF DAMS
These dams are heavy and massive wall-like structures of concrete in which the whole weight acts vertically downwards
Bhakra Dam is the highest Concrete Gravity dam in Asia and Second Highest in the world.
Bhakra Dam is across river Sutlej in Himachal Pradesh
The construction of this project and implimentation was started in the year 1948 and was completed in 1963 .
These type of dams are concrete or masonry dams which are curved or convex upstream in plan
This shape helps to transmit the major part of the water load to the abutments
Arch dams are built across narrow, deep river gorges, but now in recent years they have been considered even for little wider valleys.
They are trapezoidal in shape
Earth dams are constructed where the foundation or the underlying material or rocks are weak to support the masonry dam or where the suitable competent rocks are at greater depth.
Earthen dams are relatively smaller in height and broad at the base
They are mainly built with clay, sand and gravel, hence they are also known as Earth fill dam or Rock fill dam
TYPES OF EMBANKMENT DAMS
DISADVANTAGE: WATER CAN EASILY PASS THRU
SELECTION OF SITES
@PLACE MUST BE SUITABLE
@NARROW GORGE OR SMALL VALLEY
WITH ENOUGH CATCHMENT AREA
2.> TECHNICALLY. -
A. SHOULD BE STRONG, IMPERMEABLE, AND STABLE.
B. STRONG ROCKS LEADS TO BETTER DESIGNS .
C. IMPERMEABLE SITES ENSURES BETTER STORAGE
D. STABILITY WITH REFERENCE SEISMIC SHOCKS AND SLOPE FAILURES AROUND THE DAM ARE A GREAT RELIEF TO THE PUBLIC AS WELL AS THE ENGG.
3.> CONSTRUCTIONALLY. -
A. SHOULD BE NOT FAR OFF FROM DEPOSITS OF MATERIALS WHICH WOULD BE USEFUL FOR CONS.
B. NATURAL MATERIALS OF CONS. LIKE EARTH,SAND,GRAVEL,
AND ROCK SHOULD BE EASILY FEASIBLE OR THE COST WILL INCREASE.
4.> ECONOMICALLY. -
BENEFITS ARISING SHOULD BE REALISTIC AND JUSTIFIED IN TERMS
OF LAND IRRIGATED OR POWER GENERATED OR FLOODS AVERTED
OR WATER STORED.
5.> ENVIRONMENTALLY. –
A. THE SITE OF THE DAM SHOULD NOT INVOLVE ECOLOGICAL DISORDER ( IN THE LIFEOF PLANTS,ANIMALS AND MAN).
B. THE FISHES IN THE STREAMS ARE ALSO AFFECTED , SO THINGS SHOULD ALSO BE CONSIDERED.
C. THE DAM AND THE ASSOCIATED RESEVOIR SHOULD BECOME AN ACCEPTABLE ELEMENT OF THE ECOLOGICAL SET UP OF THE AREA.
GEOLOGICAL CHARACTERS FOR INVESTIGATION
1. GEOLOGY OF THE AREA
The area should reveal the following:-
# main topographic features
# natural drainage patterns
# general characters and structures of rock formations such as their
stratification , folding and faulting
2. GEOLOGY OF THE SITE
* This is the most imp feature that must be known thoroughly at the site all around and below the valley.
* Surface and subsurface studies using the conventional and latest techniques of geological and geophysical investigations are carried out.
THIS IS OF GREAT SIGNIFICANCE AS IT REVEALS WHAT TYPE OF ROCKS MAKE UP THAT AREA: IGNEOUS,SEDIMENTARY OR METAMORPHIC.
THIS INVOLVES DETAILED MAPPING OF PLANES OF WEAKNESS LIKE BEDDING PLANES,CLEAVAGE,JOINTS,FOLDING,FAULT ZONES
BECAUSE EACH ON OF THESE FEATURES MODIFIES THE ENGG PROPERTIES OF THE ROCKS TO A GREAT EXTENT.
** SHEAR ZONES MUST BE TREATED WITH CAUTION.IN SOME CASES THESE MAY DEVELOP TO SUCH AN EXTENT THAT IT HAS TO BE TREATED BY BACKFILLING , GROUTING
DIP AND STRIKE
* THE STRENGTH OF THE SOUND,UNFRACTURED STRATIFIED ROCKS IS ALWAYS GREATER WHEN THE STRESSES ARE ACTING NORMAL TO THE BEDDING PLANES THAN IF APPLIED IN OTHER DIRECTIONS.
* AS SUCH, GENTLY UPSTREAM DIPPING LAYERS OFFER BEST RESISTANCE FORCES IN A DAM.
* THE MOST UNFAVOURABLE STRIKE DIRECTION IS THE ONE IN WHICH THE BEDS STRIKE PARALLEL TO THE AXIS OF THE DAM AND THE DIP IS DOWNSTREAM.
FAULTS (CAN BE A SOURCE OF DANGER)
* FAULTED ROCKS ARE GENERALLY SHATTERED ALONG THE RUPTURE OF THE SURFACES
* DIFFERENT TYPES OF ROCKS CAN BE PRESENT ON EITHER SIDE OF A FAULT PLANE. HENCE IT REQUIRES A GREAT CAUTION IN BUILDING THE DAM BECAUSE IF THESE FAULTS GETS OVERLOOKED THEN THE STABILITY OF THE DAM GETS ENDANGERED.
* DAMS FOUNDED ON THE BEDS TRAVERSED BY FAULT ZONES AND ON MAJOR FAULT ZONES ARE MORE LIABLE TO SHOCKS DURING AN EARTHQUAKE.
* IT IS,THEREFORE , ALWAYS DESIRABLE TO AVOID RISK BY REJECTING SITES TRAVERSED BY FAULTS,FAULT ZONES AND SHEAR ZONES FOR DAM FOUNDATION.
* THE MOST NOTABLE EFFECTS OF FOLDS ON ROCKS ARE: SHATTERING AND JOINTING ALONG THE AXIAL PLANES AND STRESSING OF THE LIMBS.
* DAMS ALIGNED ALONG AXIAL REGIONS OF FOLDS WOULD BE RESTING ON MOST UNSOUND ROCKS IN TERMS OF STRENGTH.
* IN SYNCLINAL BENDS DAMS PLACED ON THE UPSTREAM LIMBS WOULD RUN THE RISK OF LEAKAGE FROM BENEATH THE DAM.
* NO SITES ARE FREE FROM JOINTING.
* HOWEVER, THE DETAILED MAPPING OF ALL THE ASPECTS AND CHARACTERS OF JOINTING AS DEVELOPING IN THE ROCKS OF THE PROPOSED SITES HAS TO BE TAKEN UP WITH GREAT CAUTION.
* OCCURRENCE OF MICROJOINTS SHOULD BE DEALT WITH GREAT CARE. BECAUSE IF IT IS LEFT UNTREATED ,COULD BECOME A SOURCE OF MANY RISKS.
FORCES ACTING ON A DAM
1. WEIGHT OF THE DAM
# IN GRAVITY DAMS AND EMBANKMENT DAM THE WEIGHT OF THE DAM IS THE MAJOR FORCE ACTING FOR HOLDING THE WATER BACK ON THE UPSTREAM SIDE.
# THE FORCES ARISING DUE TO THE WEIGHT OF THE DAM ARE COMPRESSIVE IN NATURE.
2. WATER PRESSURE
# THE DAM IS REQUIRED TO RESIST HORIZONTAL FORCES ACTING DUE TO WEIGHT OF THE WATER IMPOUNDED ON IT.
# THIS WATER PRESSURE CAN BE CALCULATED BY HYDROSTATIC PRESSURE DISTRIBUTION.
3. UPLIFT PRESSURE
# IT IS ALMOST IMPOSSIBLE TO MAKE A DAM IMPERVIOUS STRUCTURE .
# MANY MINUTE CRACKS AND PORES ARE LEFT IN THE DAM AND THE FOUNDATION BODY.
# WATER IS LIKELY TO FIND ITS WAY INTO THESE MINUTE OPENINGS THROUGH SEEPAGE AND GRADUALLY FILL THEM UP.
# IT EXERTS AN UPWARD PRESSURE ON THE BODY OF THE DAM WHICH IS,IN NO CASE,UNIMPORTANT.
4. EARTHQUAKE FORCES
# THE DISTURBANCE IN DAMS IS HIGHLY DANGEROUS BECAUSE THEY STORE HUGE VOLUMES OF WATER.
# DAMS BUILT IN THE AREAS KNOWN TO BE SEISMICALLY ACTIVE MUST BE DESIGNED TO WITHSTAND ADDITIONAL FORCES THAT ARE LIKELY TO ARISE IN A FUTURE SHOCK.
# SOME OF THE ADDITIONAL FORCES ARE:-
1. FORCES DEVELOPING DUE TO VERTICAL ACCELARATION OF THE GROUND BOTH IN UPWARD AND DOWNWARD DIRECTION
2. FORCES ARISING DUE TO THE HORIZONTAL ACCELARATION WHEN THE RESERVOIR BEHIND THE DAM IS EMPTY.
3. HORIZONTAL FORCES ARISING WHEN THE RESEVOIR IS FULL.
Joined: Apr 2012
17-08-2012, 03:53 PM
dam course.ppt (Size: 1.31 MB / Downloads: 66)
(a) According to hydraulic design dams may be classified as:
(i) Non-overflow dams (ii) Overflow dams.
In non-over flow dams the height of the dam is so chosen that under no circumstances water is allowed to overtop the dam. Almost all dams are made non-overflow type with provision of surpassing the excess flow through outlets or over a short and selected stretch of the part of the dam designed to allow over-topping.
Overflow dams allow the surplus water to pass over the body of the dam. A most common example of this type of dam is a concrete or masonry spillway.
A dam resisting the pressure of impounded water by an arch principle, especially a dam having in plan the form of a single arch abutted by natural rock formations.
Arch dams require a high level of stress and force analysis in order to create a sufficient design.
The main force against an arch dam is the hydrostatic pressure provided by the reservoir behind it, uplift, which is water pressure beneath the dam, the weight of the dam itself, and all the forces combined.
Other forces that affect a dam include, but are not limited to, temperature, chemical reactions, settling, silt accumulation, and earthquakes
Arch-gravity dam, curved-gravity dam having the characteristics of both an arch dam and a gravity dam.
It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam.
It combines the strengths of two common dam forms and is considered a compromise between the two.
They are generally made of reinforced concrete which provides more strength compared to normal concrete.
A gravity dam requires a large volume of internal fill.[ An arch-gravity dam can be thinner than the pure gravity and requires less internal fill
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