Seminar On Dams

Seminar On Dams

Sl.NoTitlePage No.

1Introduction4

2Types of dam:-Gravity damArch damEarthen dam5

3Types of earthen dam6

4Site selection for dams6

5Geological investigation7

6Faults while construction8

7Fold8

8Joints in dam9

9Forces acting on dam9

10Spillway10

11Impact assessment11

12Environmental Impact11

13Dam Failure11

14Main causes of failure of dam12

15Conclusion13

16Bibliography14

CONTENT

Dams

Definition:-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:

Hydropower Irrigation Water for domestic consumption Drought and flood control For navigational facilities Other additional utilization is to develop fisheries

TYPES OF DAMS

GRAVITY 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 was started in the year 1948 and was completed in 1963 .

In a gravity dam, the force that holds the dam in place against the push from the water is Earths gravity pulling down on the weight of the dam itself. In a gravity dam, stability is secured by making it of such a size and shape that it will resist overturning, sliding and crushing at the toe. The dam will not overturn provided that the moment around the turning point, caused by the water pressure, is smaller than the moment caused by the weight of the dam

ARCH DAM

Arch dams are built across narrow, deep river gorges, but now in recent years they have beenconsidered even for little wider valleys.An arch dam is a type of dam that is curved and commonly built with concrete. The arch dam is a structure that is designed to curve upstream so that the force of the water against it, known as hydrostatic pressure, presses against the arch, compressing and strengthening the structure as it pushes into its foundation or abutments. An arch dam is most suitable for narrow gorges or canyons with steep walls of stable rock to support the structure and stresses.

EARTH DAMS:

An embankment dam is a massive artificial water barrier. It is typically created by the emplacement and compaction of a complex semi-plastic mound of various compositions of soil, sand, clay and/or rock. It has a semi-permanent waterproof natural covering for its surface, and a dense, waterproof core. This makes such a dam impervious to surface or seepageerosion.They are mainly built with clay, sand and gravel, hence they are also known as Earth fill dam or Rock fill damThey are trapezoidal in shapeEarth 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 baseEmbankment dams are made from compacted earth, and have two main types, rock-fill and earth-fill dams. Embankment dams rely on their weight to hold back the force of water, like the gravity dams made from concrete.

TYPES OF EMBANKMENT DAMS Simple Embankment (homogeneous throughout) Impervious Foundation Impervious Core (Zoned embankments)

DISADVANTAGE: Water can easily pass through it and less durable than other type dams.The height of this dam is less

SELECTION OF SITES

1. Topographically:-

Place must be suitable. Narrow gorge or small valley with enough catchment areas.

2. Technically:-

Should be strong, impermeable, and stable. Strong rocks leads to better designs. impermeable sites ensures better storage Stability with reference seismic shocks and slope failures around the dam are a great relief to the public as well as the engineering.

3. Constructionally: -

Should be not far off from deposits of materials which would be useful for construction 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 termsof land irrigated or power generated or floods averted or water stored.

5. Environmentally:

The site of the dam should not involve ecological disorder (in the life of plants, animals and man). The fishes in the streams are also affected, so things should also be considered. The dam and the associated reservoir 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

Lithology

* 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.

Structures

This involves detailed mapping of planes of weakness like bedding planes, cleavage, joints, folding, fault zonesbecause each one of these features modifies the engineering 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 unfavorable 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 get 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.

FOLDS

* 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.

JOINTS

* 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 micro joints 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.

5. Some Of The Additional Forces Are:-

Forces developing due to vertical acceleration of the ground both in upward anddownward direction Forces arising due to the horizontal acceleration when the reservoir behind the dam is empty. Horizontal forces arising when the reservoir is full.

SPILLWAYA spillway is a structure used to provide the controlled release of flows from a dam or levee into a downstream area, typically being the river that was dammed. In the UK they may be known as overflow channels. Spillways release floods so that the water does not overtop and damage or even destroy the dam. Except during flood periods, water does not normally flow over a spillway. In contrast, an intake is a structure used to release water on a regular basis for water supply, hydroelectricity generation, etc. Floodgates and fuse plugs may be designed into spillways to regulate water flow and dam height. Other uses of the term "spillway" include bypasses of dams or outlets of a channels used during high-water, and outlet channels carved through natural dams such as moraines.

IMPACT ASSESSMENTImpact is assessed in several ways: the benefits to human society arising from the dam (agriculture, water, damage prevention and power), harm or benefits to nature and wildlife (especially fish and rare species), impact on the geology of an area - whether the change to water flow and levels will increase or decrease stability, and the disruption to human lives (relocation, loss of archeological or cultural matters underwater).

ENVIRONMENTAL IMPACTReservoirs held behind dams affect many ecological aspects of a river. Rivers topography and dynamics depend on a wide range of flows whilst rivers below dams often experience long periods of very stable flow conditions or saw tooth flow patterns caused by releases followed by no releases. Water releases from a reservoir including that exiting a turbine usually contains very little suspended sediment, and this in turn can lead to scouring of river beds and loss of riverbanks. A large dam can cause the loss of entire ecospheres, including endangered and undiscovered species in the area, and the replacement of the original environment by a new inland lake.Large reservoirs formed behind dams have been indicated in the contribution of seismic activity, due to changes in water load and/or the height of the water table.DAM FAILUREA dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundments. Most dams have a section called a spillway or weir over which, or through which, water flows, either intermittently or continuously, and some have hydroelectric power generation systems installed.Dams are considered "installations contain dangerous forces" under International Humanitarian Law due to the massive impact of a possible destruction on the civilian population and the environment. Dam failures are comparatively rare, but can cause immense damage and loss of life when they occur.

MAIN CAUSES OF DAM FAILURE

Common causes of dam failure include: Sub-standard construction materials/techniques Spillway design error Geological instability caused by changes to water levels during filling or poor surveying Sliding of a mountain into the reservoir Poor maintenance, especially of outlet pipes Extreme inflow Human, computer or design error Internal erosion, especially in earthen dams.

CONCLUSION

Generally there are mainly the three types of dam which are selected on the basis of need of water requirement and our basic need such as :- Hydropower Irrigation Water for domestic consumption Drought and flood control For navigational facilities Other additional utilization is to develop fisheries

India is a agricultural country so the basic need for the agriculture is water and due to the reason drought in some area it is necessary built up the dams and the selection of dams in rural areas are the earthen dams due to the funding. Dams such as gravity or arch require high initial cost and the construction process requires big time.

Due to some of the carelessness while the construction it hampers the life and strength so it is necessary to study the basic concept of the dams.

Utilization of dam water also promotes the production of the hydroelectricity.

BIBLOGRAPHY

BOOKS:-

The Design and Construction of Dams, 8th ed. (1927)By: -E. WEGMANN Engineering for Dams, 3 vol. (1945)By: -J. HINDS Irrigation engineeringBy: - V.K.SonarkarBy: -S.D.Nimbalkar