1. C.K.PITHAWALA COLLEGE OF ENGINEERING & TECHNOLOGY
SITE ASSESSMENT AND SELECTION OF
TYPES OF DAM
PRESENTED BY:
PATEL KUSH
PATEL MONEX
PATEL PARIN
PATEL RAHUL
PATEL RAVI
PROF. TANDRA BANERJEE
(Faculty guide)

2. Classification of Dams:
Gravity Dams,
Arch Dams,
And Buttress
Earth Dam And Rock fill Dam

3. Parameter of selecting a dam site:
The main parameters to be taken into account in choosing a dam site and type are the following:
1 Suitable foundation
2 Topography
3 Site of spillway
4 Construction material
5 Reservoir and catchment area
6 Communication
7 Location
8 cost

4. 1 SUITABLE FOUNDATION:
Suitable foundation should be available at the site selection for a particular type of dam.
For gravity dam ,sound rock is essential.
For earth dams, any type of foundation is suitable with proper treatment. in general , however, the foundation should be free from seams, open pocket, or fault planes.
No dam should be built across a fault known to have been active in recent times.
The best condition are when a dam can be on one uniform formation.
It is sometimes possible to improve the foundation by adopting appropriate foundation treatment.

5. 2 TOPOGRAPHY:
As far as possible the dam should be located where the river has a narrow gorge which opens out upstream to create a large reservoir.
In that case , the length of the dam would be small and the capacity of the reservoir on its upstream would be large.
A major portion of the dam should be on high ground as this would reduced the cost and facilitate drainage.

7. 3 SITE OF SPILLWAY:
Good site for the location of a separate spillway is essential especially in the case of earth or rock fill dam.
However , in case of gravity dam , spillway may be located as its middle.
The best site for a dam may be considered to be one where a deep gorge and a flank as its side are separated by a hillock.
In that case of main dam can be located in the goege and spillway can be constructed in the saddle.

10. 4 CONSTRUCTION MATERIALS:
The dam requires a large quantity of materials for its construction.
Suitable type of material in sufficient quantity should be available at neat the dam site to reduce the cost.

11. 5 RESERVOIR AND CATCHMENT AREA:
The reservoir site should be such that quantity of leakage through its side and bed in minimum.
The reservoir side should be such that it avoid or exclude water from those tributaries which carry high percentage of silt in water.
The side should be such that a deep reservoir is formed.
The cost of land and property submerged in water spread area should be minimum.
The reservoir basin on the upstream of the dam should preferably be cup shaped , with a flat bottom but steep slopes.

12. 6 COMMUNICATON:
It would be preferable to select a site which is connect by a road or rail link or can be conveniently connect to the site for transportation of cement , machinery, food , and other equipment.

13. 7 LOCALITY:
The surrounding near the site should be healthy and free of mosquitoes etc. as labour and staff colonies have to be constructed near the site.
8 COST:
The side should be such that it entails the minimum overall cost od the project , including subsequent maintenance.

14. 1 GRAVITY DAM: 1 SUITABLE FOUNDATION:
For gravity dam , sound rock is essential. The suitable foundation for graity dam is gravel and coarse sand foundation. A dam is built on a soil or rock foundation, depending on the type of dam. The foundation must be strong enough to carry the weight of the dam, and the water pressures acting on the dam. The dam foundation is below the original ground level.
Sometimes, areas of weaker soils or rocks are found below the planned foundation level and these have to be removed and replaced with stronger materials
Some rock foundations have cracks and fissures in them. These have to be filled with grout to stop water leaking out from the reservoir through the cracks once the dam is completed. This is done by drilling holes down into the rock, and by pumping grout into them, which spreads outwards to fill the cracks
For this type of dam, it is essential to have an impervious foundation with high bearing strength

15. 2 TOPOGRAPHY: Hard rock at or near the surface.
Depth of soft material above the rock should not exceed 7-10m thereby avoiding excavation.
Materials for concrete, i.e. aggregate, stone and sand should easily be accessible within 5-10 miles.
Gravity dams are suited when the length of the crest is five times or more than the height of the dam

16. 3 SITE FOR SPILLWAY: in case of gravity dam , spillway may be located at its middle.

17. 4 CONSTRUCTION MATERIALS:
A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by utilizing the weight of the material alone to resist the horizontal pressure of water pushing against it. Gravity dams are designed so that each section of the dam is stable, independent of any other dam section.
The most common classification of gravity dams is by the materials composing the structure:
Concrete dams include
mass concrete dams, made of:
conventional concrete: Dworshak Dam, Grand Coulee Dam
roller-compacted concrete: Willow Creek Dam (Oregon), Upper Stillwater Dam
masonry: Pathfinder Dam, Cheesman Dam
hollow gravity dams, made of reinforced concrete: Braddock Dam

18. 5 RESERVOIR AND CATCHMENT AREA:
Following assumption taken for gravity dam:
The dam that makes up the catchment should be bare and free of vegetation/soil. It should have no fractures, cracks, or soil pockets that would result in a loss of water through seepage.
The dam should be built in a site that has a high depth to surface ratio (it is more deep than it is wide) so as to minimize evaporation losses.
Site the dams to maximize the natural topography – to get the best storage volume, build on gorges between rocks, rock pools, and rock shelves. Make dams on the lower side of existing rock pools.
Catchment may be enclosed by stone gutters (a stone wall built with rough stone/hardcore, joined with mortar)
There should be no severe soil erosion in the catchment area

19. 2 ARCH DAM: 1 SUITABLE FOUNDATION:
solid rock foundation is suitable for arch dam.
For the design of general high arch dam, using weakly weathered rocks for some parts of the dam foundation surface is generally acceptable, which can be verified by the common stress analysis method, calibrated by foundation anti-sliding stability analysis and foundation reinforcement methods for super-high arch dams built in remote mountainous and gorge areas and/or high seismic intensity areas, the geological survey for the foundation of riverbed dam section may be insufficient in the feasibility study stage in comparison to the technical construction stage
The foundations and abutments must be competent not only to support the dead weight of the dam on the foundation but also the forces that are directed into the abutments because of arch action in response to the forces acting on the dam.

20. 2 TOPOGRAPHY:
The chief geological criterion is that the rock must be absolutely reliable to bear 2-3 MPa or more without any appreciable settlement.
The thick arch dam can be built where the crest chord-height ratio is between 3 and 5.
Thin arch dams require valleys to have a crest chord-height ratio of under 3, with a radius of under 150m.
For thin arch dam, The pressure exerted on the valley sides is between MPa

21. 3 SITE FOR SPILLWAY: in case of arch dam , spillway is also located at its centre.

22. 4 CONSTRUCTION MATERIAL:
Arch dams are often built is very narrow valleys, gorge ways, or mountainous regions where there is limited access to construction materials and naturally strong abutments. These valleys or gorge ways are more likely to be V-shaped as opposed to U-shaped
Arch dams use an upstream-facing arch to help resist the force of the water. They are typically built in narrow canyons and are usually made of concrete. Good contact between the concrete and the bedrock are required to prevent leakage and ensure stability

23. 3 BUTTRESS DAM: 1 SUITABLE FOUNDATION:
Solid rock foundation is suitable for buttress dam.
Buttress dams are made from concrete or masonry. They have a watertight upstream side supported by triangular shaped walls, called buttresses. The buttresses are spaced at intervals on the downstream side. They resist the force of the reservoir water trying to push the dam over.
The buttress dam was developed from the idea of the gravity dam, except that it uses a lot less material due to the clear spaces between the buttresses. Like gravity dams, they are suited to both narrow and wide valleys, and they must be constructed on sound rock

24. The buttresses are supported on the mat or a raft foundation
The buttresses are supported on the mat or a raft foundation. In soil(where the hard foundation is available in deeper strata in case of hard/rocky foundation) the buttresses are supported on a spread footing

25. 2 TOPOGRAPHY:
The buttress dam is suitable where the rock is capable of bearing pressures of Mpa
. Buttress dams require between a half and two thirds of the concrete required for a gravity section, hence making it more economical for dams over 14m.
Threat of deterioration of concrete from the impounded water is more likely than from a thick gravity section.
There is also an elimination of a good deal of uplift pressure, the pressure resulting from the water in the reservoir and possibly of water from the hillside rocks gaining access through or under any grout curtain and exerting upwards underneath the mass concrete dam

26. 3 SITE FOR SPILLWAY: The nappe shaped spillway crest has been provided with flash boards (wooden planks kept in position by steel pipes) to allow operation of the dam above the full supply level while retaining the flood capacity

27. 4 CONSTRUCTION MATERIAL:
A buttress dam is also commonly known as a hollow dam because the buttresses do not join together to form an actual solid wall across the river valley. The shape of the actual buttress or support is mostly flat or curved with most buttress dams today being constructed out of concrete and reinforced steel. Another common characteristic of the buttress dam is that the upstream face of the dam is inclined at about 45 degrees

28. 4 EARTH DAM AND ROCK FILL DAM:
1 SUITABLE FOUNDATION:
For the earth dam,
Any foundation with proper treatment should be suitable
The best foundation condition is bed with dip along the upstream and strike along the valley.
Foundation should be free from the holes and faults.
For the rock fill dam,
They required foundation which will result in minimum settlement.
The foundation free from the all foreign materials like silt, sand, clay etc.

29. 2 TOPOGRAPHY:
For earth dam,
Near the site there must be clay to fill the trench and embanking material capable of standing safely, without slipping, to hold up a clay core.
An advantage of earthen embankments is that troubles due to the deterioration of the structure by peaty waters of low pH do not arise
For rock fill dam,
Rock fill dams can be built where the following conditions exist -
Uncertain or variable foundation which is unreliable for sustaining the pressure necessary for any form of concrete dam.
Suitable rock in the vicinity which is hard and will stand up to variations of weather.
An adequate amount of clay in the region which may be inserted in the dam either as a vertical core or as a sloping core. Accessibility of the site and the width of the valley is suitable for the manipulation of heavy earth-moving machinery, caterpillar scrapers, sheep foot rollers and large bulldozers.

30. 3 SITE FOR SPILLWAY:
The size, type, and restrictions on location of the spillway are often controlling factors in the
choice of the type of dam. When a large spillway is to be constructed, it may be desirable to combine the
spillway and dam into one structure, indicating a concrete overflow dam. In some cases where requiredexcavation from the spillway channel can be utilized in the dam embankment, an earth or rock-fill dam may be advantageous

31. Spillway in earth dam:

32. Spillway in rock fill dam:

33. 4 CONSTRUCTION MATERIAL:
Following material are use for earth dam:
Clayey material
Black cotton soil , silty clayey loam , for heating and cutoff
Sandy material
Murum , soft rock , sandy silt , for casting
Rock
For pitching and riprap , rock masonry etc.
Sand
For filters , seepage drain and masonry
Cement , steel , lime and other building material in small quantities
Rockfill dam are constructed mainly from rockfill or pieces of rock.

35. Thank you