ARCH DAM

DAM• 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

Structure of Dam

Heel

Gallery

Toe

Spillway(inside dam)

Crest

NWLNormalwater level

MWLMax. level

Free boardSluice way

Upstream Down stream

• Heel: contact with the ground on the upstream side.• Toe: contact on the downstream side.• Abutment: Sides of the valley on which the structure of the

dam rest.• Galleries: small rooms like structure left within the dam

for checking operations.• Diversion tunnel: Tunnels are constructed for diverting

water before the construction of dam. This helps in keeping the river bed dry.

• Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side.

• Sluice way: An opening in the dam near the ground level, which is used to clear the silt accumulation in the reservoir side.

• 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.

Arch Dam

a

Arch dam• Used in narrow sites with abutments.

• Use, less concrete than gravity dam.

• More difficult to design and construct than gravity dam.

Arch and buttress dam• Efficient use of concrete ,used where a strong

foundation exists.• Very difficult to design and a construct..

TYPES OF ARCH DAM

1) Constant radius arch dams.

2) Constant angle arch dams.

3) Variable radius arch dams.

4) Double curvature (or)cupola arch dams.

5) Arch gravity dams.

CONSTANT RADIUS ARCH DAM

• A constant radius arch dam is the

One in which the radius of the

extrados(or outside curved surface of the arch) is constant at all elevations from top of the dam to its base.

• However the intrados (or inside curved surface of arch) has gradually decreasing radius as the depth below the crest increases,to provide the increased thickeness needed for the higher reservoir water pressure.

• Thus in this case the upstream face of the dam is vertical and the dam is triangular in cross-section with increased width at the crest.

• Further in a constant radius arch dam the centres for extrados,intrados and the centre lines of the horizontal arch rings at various elevations lie on a straight vertical line that passes through the centre of the upstream face of the horizontal arch ring at the crest.

CONSTANT ANGLE ARCH DAM

• A constant angle arch dam is the one in which the central angle of the arch rings at all elevations from top of the dam to its base has the same magnitude.

• According to thin cylinder theory of design of arch dams, the volume of concrete required for an arch dam is minimum if the central angle of the arch rings is 133º34’.

• However, in actual practice for the economical design of constant angle arch dams the central angle may be in the range of 100º to 150º,depending upon the valley shape.

• This is so because the cost of shuttering which depends on the valley shape is not included in the calculation of minimum volume of concrete by thin cylindar theory.

VARIABLE RADIUS ARCH DAM

• A variable radius arch dam is the one in which the radii of extrados and intrados of the arch rings at various elevations from the top of the dam to its base vary.

• The radius is maximum at the top of the dam and minimum at its base.

• Further in this case the central angle of the arch rings at various elevations from top of the dam to its base also vary, being maximum at the top of the dam and minimum at its base.

• The central angles of the arch rings usually range from 80º to 150º and these are so adjusted that as far as possible larger are action is developed even for arch rings at lower elevations.

DOUBLE CURVATURE (OR) CUPOLA ARCH DAM

• A double curvature or cupola arch dam is the one which has curvature in horizontal as well as vertical planes. In other words it is a dam which is curved in plan as well as in sections.

• These dams are also known as shell arch dams because these are usually designed as shell structures.

• The double curvature or cupola arch dams were originated and developed in Italy.

• In general these dams have relatively small thickness and hence these are quite economical.

ARCH GRAVITY DAM

•A thick arch dam is known as arch gravity dam because structurally it behaves as both gravity and arch dam.•The famous HOOVER dam in U.S.A, is an arch gravity type dam.

• For an arch gravity dam generally in the lower part of the valley the extrados of the arch rings have gradually increasing radii so that near the base of the dam the upstream face has a batter and hence the base width of the dam is considerably increased.

FORCES ON AN ARCH DAM• The various forces acting on

an arch dam are same as those which act on a gravity dam.However, the relative importance of the forces is different in arch dams.

• Because of the narrow basewidth of an arch dam the uplift pres is less important than for a gravity dam.

• On the other hand the stresses caused by ice pressure,temperature changes and yielding of supports are very important in arch dam.

ReservoirForce

JURISDICTIONAL

If dam is 15 feet in height or greater as measured from the highest point on the crest of the dam to the lowest point on the down stream toe, and

If the dam has an impoundment capacity of 10 acre-feet or greater as measured at the highest point on the crest of the dam.

JURISDICTIONAL DAMS – HIGH HAZARD POTENTIAL

If failure of the dam could result in loss of human life or significant damage to property below the dam regardless of height or impoundment capacity.

HAZARD POTENTIAL CLASSIFICATIONS DEFINITION

Hazard potential means the probable damage that would occur if the structure failed, in terms of loss of human life and economic loss or environmental damage.

HAZARD POTENTIAL CLASSIFICTIONS

a) LOW (CLASS A) – No loss of life or significant property damage expected.

b) INTERMEDIATE (CLASS B) – No loss of life expected but may cause significant property damage.

c) HIGH (CLASS C) – Loss of life possible and severe property damage probable.

WHY ARE CLASSIFICATIONS IMPORTANT ?

As size and hazard goes up the design must be more comprehensive.

High hazard potential dams get more frequent routine inspections.

During emergencies , high hazard and larger dams are inspected first.

As hazard goes up enforcement efforts increase.

ENGINEERING REQUIREMENT

• All work on jurisdictional dams beyond routine maintenance must be designed by a licensed engineer and submitted by approval.

“THANKS TO ALL ”

by,

jo

stin p jose

kamaleswaran k