Forces Acting On Gravity Dam

Forces Acting On Gravity Dam

A Gravity dam is described as a stable structure, manufactured from concrete or masonry, built throughout a river to create a reservoir on its upstream.
The segment of the Forces Acting On Gravity Dam is triangular in form with its apex at its top and the most width on the bottom. The segment is so proportioned that it resists the outside pressure performing on it through its very own weight.
When this kind of structure is maximum long-lasting and requires very little maintenance. Nowadays, concrete gravity dams choose in comparison to different dams.
They may be built simply on any dam site, wherein a herbal basis sturdy sufficient to undergo the full-size weight of the dam is available.

Dam

The dam is a softened barrier made at an acceptable location across a river natural depression to store flowing water.

Storage of water is utilized for following objectives:

  • Hydropower:- Hydropower or hydro-energy, is a type of renewable energy that uses the water hold on in dams, also as flowing in rivers to make electricity in hydropower plants.
  • Irrigation:- Irrigation is the technique of making use of water to the vegetation artificially to fulfill their water requirements. Nutrients will also be supplied to the vegetation via irrigation. The diverse reasserts of water for irrigation are wells, ponds, lakes, canals, tube-wells, or even dams. the delivery of water to land or vegetation to assist growth, normally by using channels.
  • Water for domestic consumption:-Domestic water use is water used for indoor and outdoor household purposes— all the items you are doing at home: drinking, making ready food, bathing, laundry garments, and dishes, brushing your teeth, gardening, and even washing.
  • Drought and flood control:- Flood control methods are accustomed to cut back or forestall the prejudicial effects of floodwaters. Flood relief methods are used to Dec the consequences of floodwaters or high water levels.
  • For navigational facilities:- GPS technology as soon as tracked submarines, and nowadays a miles greater effective gadget allow you to search out a ham and swiss sub.
  • Another additional utilization is to develop fisheries:- The integrated method of knowledge gathering, analysis, planning, consultation, decision-making, allocation of resources and formulation and implementation, with social control as necessary, of rules or rules that govern fisheries activities so as to make sure the continuing productivity of the resources and therefore the accomplishment of different fisheries objectives.
Forces Acting On Gravity Dam
Forces Acting On Gravity Dam

Force Acting On Dam Structure

  1. Weight of the dam
  2. Uplift pressure or Seepage Loads
  3. Earthquake Forces
  4. Self-Weight of Dam
  5. Silt Pressure
  6. Wave Pressure
  7. Ice Pressure
  8. Uplift pressure
  9. Water Pressure

1 Weight of the dam

The weight of the dam is that the main stabilizing force within the gravity dam. Generally, for analysis purposes, the unit dimension of the dam consider. once the cross-sectional of the dam might divide into many rectangles and triangles, and therefore the weights w1, w2, and w3, etcetera of every of those are often determined, beside the determination of their lines of action. the overall weight of the dam acts at the middle of gravity of its section

Weight of the dam

2 Self-Weight of Dam

The weight of dam and its foundation is a major resisting force. It can be computed using the following equation:

 W = \gamma_{m}Volume
where,   \gamma_{m} = unit\: weight\: of \:dam \:material

3 Uplift pressure or Seepage Loads

When the water is held on the upstream side of a dam there exists a head of water capable the peak up to that the water is stored.
This water enters the pores, fissures, and cracks of the foundation material below pressure. It additionally enters the joint between the dam and also the foundation at the bottom and the pores of the dam itself.
This water then seeps through and tries to emerge out on the downstream end. The leaky water creates a hydraulic gradient between the upstream and downstream sides of the dam.
This hydraulic gradient causes vertical upward pressure. The upward pressure is known as an uplift that is that the second-largest external pressure. Uplift reduces the effective weight of the structure and consequently, the restoring force is reduced.
Therefore, it’s essential to check the character of uplift and additionally, some strategies can be got to be devised to cut back the uplift pressure value.

Uplift pressure or Seepage Loads

 With reference to figure 3, uplift pressure is given by:- P_{u}= \frac{WHB}{2}

Where  P_{u} is the uplift pressure, B is the bottom width of the dam and H is the peak as much as which water is stored. This overall uplift acts at B/three from the heel or upstream stop of the dam.
Uplift is usually decreased through building drainage pipes among the dam and its foundation, building reduce off partitions below the upstream face, holes withinside the dam section, or stress grouting the dame foundation

4 Earthquake Forces

Dynamic loads created because of earthquakes should be thought-about within the style of all major dams settled in ‘high-risk’ unstable regions and for dams situated in shut proximity to probably active scissure complexes.
An earthquake produces waves in each doable direction. However, it’s to be resolved into vertical and horizontal parts for design purposes. The horizontal element encompasses a larger effect.
Seismic vibration influence the dam body and water in the reservoir of the dam. So, the generated dynamic loads are due to the inertia of the dam and hydrodynamic forces by the water in the reservoir.  Seismic forces are calculable in step with the following equations:

5 Ice Pressure

The ice that is created on the water surface of the reservoir within the cold countries could generally soften and expand. The dam face is subjected to the thrust and exerted by the increasing ice.
This force acts linearly on the length of the dam and at the reservoir level. The magnitude of this force varies from 250 to 1500 kN/sq.m relying upon the temperature variations. On average, a worth of five hundred kN/sq.m is also taken beneath standard circumstances.

6 Wind pressure

Wind pressure acts on the exposed surface of the dam once winds blow. Usually, the wind pressure isn’t important for the look of gravity dams and is thus neglect. However, the construction ought to contemplate within the design. A wind pressure of one to 1.5 kN/m2 generally considers over the realm exposed to high winds.

7 Wave Pressure

Waves are generated at the floor of the reservoir through the blowing winds, which exert pressure at the top part of the dam above the water level.
This pressure has calculated the use of equation
 P_{w}=2.4\gamma_{w}h_{w}
Wave pressure depends upon wave height

For F < 32 km:
 h_{w}=0.32\sqrt{PV}+0.763-0.271xF^{\frac{1}{4}}

For F > 32 km:
 h_{w}=0.32\sqrt{VF}
Where:
 h_{w} is the height of the water from the top of the crest to bottom of the trough in meters.
V is the wind velocity in km/hour
F is the fetch or straight length of a water expanse in km.
The maximum pressure intensity due to wave action occurs when it acts at 0.5 meters above the still water surface.

Total force due to wave action is given by:
 P_{w}=0.5(2.4\gamma_{w}h_{w})\frac{3}{8}h_{w}

Wave Pressure

8 Silt Pressure

The weight of the dam and its foundation could be a major resisting force. It acts at h/3 from the bottom and might be computed using equation
 P_{silt}=0.5\gamma_{s}h^{2}k_{a}
Where:
 k_{a} is the coefficient of active earth pressure of silt
silt which equal to  \frac{1-sin\phi}{1+sin\phi}
 \phi is the angle of internal friction of soil, cohesion neglected.
 \gamma_{s} is the submerged unit weight of silt material.
h is the height of silt deposited.

silt pressure on a dam

9 Water Pressure

It is that the pressure of water that acts perpendicularly on the upstream face of the dam. For this, there are 2 cases:
A. Upstream face of the dam is vertical and there’s no water on the downstream aspect of the dam

Water Pressure

The overall pressure is within the horizontal direction and acts on the upstream face at a height H/3 from the bottom. The water pressure on the dam is computed per equation
 p_{1}=\frac{Wh^{2}}{2}
Where,
w is the specific weight of water. Usually, it is taken as unity.
H is the height up to which water is stored in m.
B is the Upstream face with batter and there is no water on the downstream side

Water Pressure

Here further to the horizontal water  p_{2} of equation 1, there’s a vertical pressure of the water. It is because of the water column resting at the upstream sloping side.
The vertical pressures at the length ‘b’ part of the base. This vertical pressure is calculated as follow
  p_{2}=(bxh_{2}xw)+(0.5bxh_{1}xw)

Pressure  p_{2} acts through the middle of gravity of the water column resting on the sloping upstream face.
If there’s water standing on the downstream aspect of the dam, water pressure can have a vertical and horizontal elements which may be victimization equation one except for water height that is illustrated
The water pressure on the downstream face truly stabilizes the dam. thus as a further issue of safety, it’s going to be neglected.

Water Pressure

Basic Definition Forces Acting On Gravity Dam

  • The Axis of the dam is that the line of the upstream fringe of the highest (or crown) of the dam. The axis of the dam within the arrange is termed the baseline of the dam. The axis of the dam is sometimes straight.
  • The length of the dam is the distance from one abutment to the other, measured on the axis of the dam at the extent of the top of the dam.
  • The structural height of the dam is the distinction in elevations of the top of the dam and also the lowest purpose in the excavated foundation. it, however, doesn’t include the depth of special geologic options of foundations like slender fault zones below the foundation. In general, the peak of the dam means that its structural height.
  • The maximum base width of the dam is that the maximum horizontal distance between the heel and also the toe of the max section of the dam within the middle of the valley.
  • The hydraulic height of the dam is adequate for the difference in elevations of the best-controlled water surface on the upstream of the dam and the lowest purpose in the stream bed.
  • The Heel is the contact with the bottom on the upstream side.
  • The Toe is that the contact on the downstream side.
  • The Abutment is the side of the natural depression on that the structure of the dam
  • Galleries are the tiny rooms-like structure left within the dam for checking operations.
  • A diversion tunnel is the tunnels are made for diverting water before the development of the dam. This helps to keep the stream bed dry.
  • Spillways are the arrangement close to the highest to unharness the excess water of the reservoir to the downstream side.
  • Sluice way is the gap within the dam near the bottom level, which is used to clear the silt accumulation in the reservoir side.

Advantages of Gravity Dam

  • A gravity dam needs the smallest amount of maintenance of alternative dams.
  • Gravity dams are comparatively a lot of robust and stable as compared to earth dams.
  • It will build any high wheres the high of an earth dam.
  • Gravity dam will no trial suddenly, it provides enough warning time whereas earth dams usually fail suddenly.
  • Deep-set sluices may be employed in gravity dam, to retard the geological phenomenon or silt deposit within the reservoir.

Disadvantages of Gravity dam

  • Gravity dams can be engineered solely on a sound rock foundation. whereas earth dams can be built on weak foundations or porous foundations with applicable foundation treatment.
  • The initial value of a gravity dam is often higher as compared to an associate earth dam.
  • If mechanized plants adore producing and transporting mass concrete, the natural action of concrete, etcetera isn’t available, a gravity dam might take longer to construct.
  • Gravity dams need experienced labor for is construction.

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