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What is the primary force acting on a gravity dam?
What is the primary force acting on a gravity dam?
How does water pressure on a gravity dam change with depth?
How does water pressure on a gravity dam change with depth?
What is the formula for calculating the total horizontal water force acting on a gravity dam with a vertical upstream face?
What is the formula for calculating the total horizontal water force acting on a gravity dam with a vertical upstream face?
Which of these are classified as secondary loads on a gravity dam?
Which of these are classified as secondary loads on a gravity dam?
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Why is earthquake resistance a crucial factor in the design of gravity dams?
Why is earthquake resistance a crucial factor in the design of gravity dams?
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What is the primary reason for regular inspections and testing of gravity dams after major earthquakes?
What is the primary reason for regular inspections and testing of gravity dams after major earthquakes?
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What is the primary reason gravity dams are considered very durable and require minimal maintenance?
What is the primary reason gravity dams are considered very durable and require minimal maintenance?
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What is the difference between the water load calculations for a vertical upstream face and a partially inclined upstream face?
What is the difference between the water load calculations for a vertical upstream face and a partially inclined upstream face?
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What causes a tension crack to occur at the upstream edge (heel) of a dam during overturning failure?
What causes a tension crack to occur at the upstream edge (heel) of a dam during overturning failure?
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What is the factor of safety (Fo) against overturning failure when the resultant force strikes the middle third point (e = B/6)?
What is the factor of safety (Fo) against overturning failure when the resultant force strikes the middle third point (e = B/6)?
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Which of the following factors resist sliding failure of a dam?
Which of the following factors resist sliding failure of a dam?
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What is the minimum acceptable factor of safety against sliding (Fs)?
What is the minimum acceptable factor of safety against sliding (Fs)?
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What is the typical range for the coefficient of friction (µ) between the dam and its foundation?
What is the typical range for the coefficient of friction (µ) between the dam and its foundation?
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Which of the following is NOT a common type of dam failure?
Which of the following is NOT a common type of dam failure?
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What happens to the effective width of a dam if a tension crack develops at the heel?
What happens to the effective width of a dam if a tension crack develops at the heel?
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What is the primary cause of crushing (compression) failure in a dam?
What is the primary cause of crushing (compression) failure in a dam?
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What is the formula for calculating the self-weight load of the dam when the upstream face is vertical?
What is the formula for calculating the self-weight load of the dam when the upstream face is vertical?
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Which of the following defines the condition when there is no drainage gallery and no tail water on the downstream side of the dam?
Which of the following defines the condition when there is no drainage gallery and no tail water on the downstream side of the dam?
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What is the impact of uplift forces on the stability of a dam?
What is the impact of uplift forces on the stability of a dam?
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How is the uplift force calculated when there is a drainage gallery provided and tail water is present?
How is the uplift force calculated when there is a drainage gallery provided and tail water is present?
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In the case where the upstream face of the dam is partially inclined, what is the expression for the weight load $W1$?
In the case where the upstream face of the dam is partially inclined, what is the expression for the weight load $W1$?
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What is considered the primary stabilizing force in a gravity dam?
What is considered the primary stabilizing force in a gravity dam?
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How is water seepage significantly characterized in relation to uplift loads?
How is water seepage significantly characterized in relation to uplift loads?
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What must a dam be designed to ensure according to stability requirements?
What must a dam be designed to ensure according to stability requirements?
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Study Notes
Gravity Dam Design Principles
- A gravity dam is a structure designed so its own weight resists external forces.
- This design makes it a durable and low-maintenance structure.
Types of Loads on Gravity Dams
- Loads are classified as primary, secondary, or exceptional, based on their importance and applicability.
Primary Loads
- These are major loads impacting all dams regardless of type.
- Water load: The horizontal water pressure exerted by the water on the upstream dam face. This pressure distribution is triangular.
- Self weight load: The weight of the dam itself. This is a stabilizing force.
- Related seepage (uplift) load: Pressure exerted by water seeping through the dam and foundation.
Secondary Loads
- These loads are generally applicable, but of lesser magnitude.
- Sediment load: Forces due to sediment buildup in the reservoir.
- Wind load: Forces exerted by wind.
- Ice load: Forces due to ice buildup.
- Silt load: Forces due to silt buildup in the reservoir.
- Thermal and dam foundation interaction effect: Thermal expansion and contraction of the dam.
Exceptional Loads
- These are unpredictable and significant, typically related to earthquakes.
- Earthquake loads: Forces due to seismic activity. These are a primary concern in dam design and require testing after earthquakes.
Water Loads
- Water pressure (P) is the major external force on a dam.
- The horizontal water pressure depends on the depth of the water (hydrostatic pressure distribution). The shape is a triangle.
- Two cases exist to estimate water loads: upstream face is either vertical or partly inclined and partly vertical.
Case 1: Vertical Upstream Face
- Intensity is zero at the water surface and equal to H at the base.
- Resultant force = 1/2 *w *H^2, acting at H/3 from the base.
- w = unit weight of water, H = depth (MWL - maximum water level)
Case 2: Inclined Upstream Face
- The resulting water force can be resolved into horizontal and vertical components.
- Forces can be calculated on both upstream and downstream faces.
Self-Weight Loads
- The dam's weight is a main stabilizing force.
- The weight is equal to the dam's cross-sectional area multiplied by the unit weight of the material.
- Two cases exist : the upstream face is vertical.
Uplift (Seepage) Loads
- Water seeping through the dam's pores, foundation, and joints exerts uplift pressure.
- This pressure acts to reduce the dam's stabilizing force.
- Several cases exist to calculate the uplift pressure in dams:
- No drainage, no tailwater (triangle shape)
- No drainage, tailwater present.
- Drainage gallery present, tail water present,
Stability Requirements of Gravity Dams
- The dam must be structurally stable to withstand stresses from imposed loads.
- The foundation must be strong enough to carry the loads.
- The dam must be safe against all possible failure modes with an adequate safety factor..
Possible Failure Modes
- Overturning failure.
- Sliding failure.
- Tension failure.
- Crushing (compression) failure.
Overturning failure:
- Occurs when the resultant of all forces acts outside the base.
- A factor of safety of more than 1.25 may be acceptable but is generally not ideal.
Sliding failure:
- Occurs when the dam slides along its base.
- The factor of safety against sliding should be greater than 1..
Tension failure:
- Develops at the dam's upstream edge (heel) when the resultant force acts outside the middle third.
Crushing (compression) failure:
- Occurs when the vertical stress in the dam and foundation exceeds safe limits.
- The eccentricity of the resultant force is key to calculate this type of failure.
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Description
This quiz explores the fundamental principles of gravity dam design, including the various types of loads that affect their stability. You will learn about primary and secondary loads, such as water pressure and wind forces, and how these elements influence dam construction and maintenance. Test your knowledge on this vital topic in civil engineering.
