Load combinations
LOAD COMBINATIONS

Load combinations

LOAD COMBINATIONS In Section 13.2 various forces that are likely to act on the dam have been discussed. But all these forces seldom act simultaneously on the dam. There are some combinations of the loads that may act simultaneously. Design of the dam should be based on the most adverse combination of “probable load condition”. USBR has recommended two load combinations. 1. Standard load combinations. 2. Extreme load combinations. 1. Standard Load Combinations. Under this heading three possible combinations are given. (i) Horizontal water pressure, at normal reservoir level + ice pressure + silt pressure + normal uplift pressure. But this combination is adopted where ice pressure is considerable. (ii) Horizontal water pressure at normal reservoir level + earthquake pressure + silt pressure + normal uplift pressure. (iii) Horizontal water pressure at H.F.L. + silt pressure + normal uplift pressure. 2. Extreme Load Combination. Maximum flood water elevation + silt…

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Modes of failure of gravity dams
MODES OF FAILURE OF GRAVITY DAMS

Modes of failure of gravity dams

MODES OF FAILURE OF GRAVITY DAMS A gravity dam can fail due to the following reasons: Overturning of the dam Sliding of the dam Crushing of the dam or Foundation Development of tension in the dam. 1. Overturning of the Dam. If the resultant of all the possible forces (internal as well as external) acting on the dam cuts the base of the dam downstream of the Toe, the darn would overturn unless it can resist tensile stresses. To safeguard the dam against overturning, the resultant of the forces should never be allowed to go down stream of the Toe. If resultant is maintained within the body of the dam, there will be no overturning. All the forces acting on the dam cause moments. Some of the forces help maintain stability of the dam, while others try to disturb the stability. The moments of the forces, helping dam to maintain…

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forces acting on a gravity dam
FORCES ACTING ON A GRAVITY DAM

forces acting on a gravity dam

FORCES ACTING ON A GRAVITY DAM A detailed sketch of a gravity dam is shown in Fig. 13.1. All the predominant forces, that act on the dam, have been shown in the figure itself. The forces that act on the dam are the following: Weight of the dam Horizontal hydrostatic pressure due to water Uplift pressure due to water percolated under the dam Earthquake pressure Wind pressure Ice pressure Wave pressure Pressure due to silt deposited on U/S face. Out of above eight forces, acting on the dam, first three forces are the major forces that are considered in the design. All other forces are not of much significance and are considered only under specific conditions. 1. Weight of the Dam. It is the most important force, particularly for gravity dams. Stability of the dam largely depends upon this force. For the design purpose only unit length of the dam…

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Methods of measuring the discharge
METHODS OF MEASURING THE DISCHARGE

Methods of measuring the discharge

METHODS OF MEASURING THE DISCHARGE Discharges of rivers, streams and canals can be measured by following methods: Area velocity method, Weir method, Metric flumes method, Chemicals method, Stage discharge curve method, From power plant records. 1. Area Velocity Method. This is the direct method of computing the discharge in a stream by measuring its velocity and area of flow. The methods of computing average velocity of flow and also those of area of cross-section of flow, have been discussed earlier in this chapter. The discharge is nothing but a multiplication of the average velocity of flow and that of area of cross-section of water. 2. Weir Method. Various kinds of weirs are installed across the river streams to measure the discharge. The head of water over the weir crest is measured and the discharge is calculated by using the appropriate formula. Weirs are generally used for measuring the discharge of…

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Pleading of national policy flood control
RECOMMENDATIONS OF NATIONAL POLICY ON FLOOD CONTROL

Pleading of national policy flood control

RECOMMENDATIONS OF NATIONAL POLICY ON FLOOD CONTROL Board recommendations are as follows: In order to deal the problem of floods on a comprehensive basis very sustain and systematic efforts are need, both at administration level and general public level. These tasks are very huge is magnitude and hence measures of protection from floods should be progressively undertak. Even the best flood control measures do not provide complete protection and are aim at provid reasonable degree of protection. projects, Central Govt. should also take initiative in the matter. Flood control measures should form an integrat part of the overall development of the region in respect of water resources, economic perspective, ecological and humanitarian considerations. The flood management in a particular areas should form a part of package of measures of comprehensive plan for that area. Different alternatives with various degree of min of measures should be work out and analysed for…

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Measurement of discharge streams & canals

PURPOSE OF MEASUREMENT OF DISCHARGE OF STREAMS AND CANALS The discharge of streams and canals has to be measured for following reasons. The irrigation potential of a particular river at a particular point can be estimated only if discharge characteristics of the river at that particular point of the stream are known. If flow in the stream falls too low during particular season, it may become essential to construct dam or weir. Even height of the dam or weir depends upon the discharge of the river. Storage of water is further dependent upon the available discharge which again necessitates measurement of discharge. Because water in the canal is left proportional to the area it has to irrigate, measurement of discharge again becomes necessary at all works. Regulation of canal system is almost fully based on the discharge measurement, as water in each canal has to be left equal to the…

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Some important terms
SOME IMPORTANT TERMS

Some important terms

SOME IMPORTANT TERMS 1. Normal Pool Level. This is the maximum level of water in the reservoir to which the water will rise during ordinary operating conditions. This level corresponds either to the crest level of the spillway or top level of the spillway gates. This level is also know maximum conservation level. 2. Minimum Pool Level. The lowest elevation of water which has to be maintained in the reservoir under normal operating conditions is called minimum pool level. The elevation is guided either by the lowest outlet in the dam or by minimum head required for efficient functioning of turbines. 3. Maximum Pool Level. During floods water starts flowing over the spillways. But discharge over spill-ways increases with further rise in reservoir level. The maximum level attained by water during worst design flood is know the maximum pool level. This level of water is essentially above the Normal pool…

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Some terms in most common use in regard to run-off
Some terms in most common use in regard to run-off

Some terms in most common use in regard to run-off

SOME TERMS IN MOST COMMON USE IN REGARD TO RUN-OFF 1. Hydrograph. It is a curve or plot of discharge versus time at any section of a river. It represents the flow characteristic of the river. 2. Period of Surface Run-off. It is the time taken by the surface run off to pass the given section of the river, after the surface run-off makes its first appearance at the section. 3. Period of Rise. It is the time take by the surface run-off to reach its maximum value from the time of its beginning. 4. Time of Concentration. It is the time require by the water to reach the outlet point from the most remote point of the drainage area. When a storm has been in progress for a time equal to the time of concentration. it is assume that all the part of the catchment start contributing to the…

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Measurements |Points shall be noted while taking measurements.
Measurements |Points shall be noted while taking measurements.

Measurements |Points shall be noted while taking measurements.

Measurements |points shall be noted while taking measurements. |Measurement|points shall be noted while taking measurements.|Methods of measurement|Measurement|Measurement of works| Measurement of civil engineering works occupies a very important place in planning and execution of works, right from the stage of preparation of estimate to the final completion of works and settlement of payment of the works to the contractors. There are some differences regarding the method of measurement among the State Government departments. But the method introduced by the Indian Standard (I.S.) is legal and basic document for removing ambiguities and settling all the disputes for making payment to the contractors. Following points shall be noted while taking measurements. 1. Each item shall be fully described. 2. The measurement shall be taken in the order of sequence of length, breadth or width and height or depth. 3. Dimensions shall be measured to the nearest to 0.01 m. 4. Area shall…

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Painting new wood work
Painting new wood work

Painting new wood work

Learn : Painting new wood work : Knotting or killing the knot, Application of priming coat, Stopping, Application of finishing coats. Painting new wood work   Following points should be attended to before painting new wood work:   (i)        Only well seasoned timber should be painted otherwise not only shall the paint be spoilt but also due to dry rot the timber is likely to decay early. Also the paint surface will otherwise crack due to uneven shrinkage   (ii)       It is advisable not to paint excessively dry wood.   (iii)     Paint should be applied to only dry surface. (iv)      The surface to be painted should be rendered smooth, clean and free from rust or dirt. (v)       All nails should be punched in 1/2 cm below the surface. (vi)      Large and loose knots should be cut out and filled tightly with correctly fitting wooden pieces. (vii)    The surface should be…

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