Dam Types and Design Considerations

Posted on Oct 13, 2024 in Geology

Definitions

Dam

An artificial structure that limits, in whole or in part, the outline of a facility located on the ground, for the purpose of storing water. For security purposes, pools of water can also be considered dams.

Raft

A hydraulic structure consisting of an artificial structure used for the storage of water outside of a channel and bounded wholly or partly by a retention dam.

Reservoir

A hydraulic structure consisting of an artificial site for limited water storage, bounded in whole or in part by a dam. It can also refer to the land, water storage dam, together with all auxiliary structures related to these elements and their functionality.

Dam Classification Based on Size

Large Dam

A dam with a height over 15 meters or, with heights between 10 and 15 meters, has a storage capacity exceeding 1 cubic hectometer.

Small Dam

A dam that does not meet the conditions of a large dam. Depending on the potential risk resulting from breakage or malfunction, they fall into one of three categories:

• Category A: Dams whose failure or malfunction may seriously affect urban or essential services, or cause significant environmental damage.
• Category B: Dams whose failure or malfunction can cause important environmental damage or affect a small number of homes.
• Category C: Dams whose failure or malfunction can result in moderate property damage and incidental loss of life. This category includes all dams not included in Category A or B.

Essential Services

Services that support at least 10,000 inhabitants.

Reservoir Levels (New Rules)

• Maximum Normal Level (NMN): The highest level of water retention in the reservoir reached with all mechanical elements of closed drainage control.
• Maximum Operating Level (NME): The highest level the water can reach in the reservoir during normal operation, without avenues.
• Project Avenue Level (NAP): The highest level reached in the reservoir, considering the rolling action when it receives the project avenue.
• Extreme Avenue Level (NAE): The highest level reached in the reservoir if there is an extreme avenue, in view of the rolling action.

Avenue Types

Depending on the dam’s risk classification, there are two types of tributaries to the reservoir avenues:

• Project Avenue: The maximum avenue that should be considered for sizing the spillway, drain bodies, and power dissipation structures, ensuring their proper function.
• Extreme Avenue: The maximum avenue that the dam can withstand without breaking, while accepting smaller margins of safety.

Gravity Dams

Gravity dams resist water pressure through their dead weight, transmitting the entire load to the foundation. They are suitable for rock foundations with sufficient load-bearing capacity.

Sealing

Sealing is achieved by the impermeability of the material, but it is not complete, and water flows through the pores. The pore pressure of the fluids within the pores of the structure and land decreases the effective pressures between the solid particles.

Drains

A drain is a hole through which filtered water is collected and led to a drainage system. Its purpose is to eliminate or reduce pore pressure downstream, reducing uplift.

Drain Layout

The layout of drains can be matched to the galleries within the dam to facilitate maintenance. Screen drains should be placed close to the upstream face.

Screen Shots

Screen shots are made in the dam to cut off seepage through fissures in the rocks.

Service Galleries

Used to perform maintenance and auscultation work.

Functional Boards

Due to the heat of setting and subsequent shrinkage of concrete, the dam body is constructed in alternating blocks. The unions between these blocks are called joints.

• Longitudinal Joints: Parallel to the dam axis.
• Transverse Joints: Perpendicular to the dam axis.

Construction Joints

Tend to be horizontal between tiers or blocks and are a result of the construction process.

Load Combinations

• A1 Empty Reservoir: Considers the combination of dead weight and temperature variations.
• A2 Full Reservoir: Considers the combination of self-weight, buoyancy, pore pressure, pressure of landfills, push from ice or waves caused by wind, and temperature variations. Buoyancy and pore pressure are calculated at the maximum normal reservoir level.
• B11 Seismic Shocks: Linked to the solicitations of the A1 situation.
• B21 Ineffective Drains: A2 status with ineffective drains.
• B22 Seismic Shocks with A2 Stresses: Assumes pore pressures are not affected by seismic shocks. Thrust from ice or waves may be disregarded.
• B23 Full Elevation with Extraordinary Wave Action: A2 status with full elevation to the expected level in the reservoir, including extraordinary wave action. Assumes pore pressures are not affected by over-elevation. Thrust from ice may be disregarded.

Gravity Dams: Compacted Concrete

Economically advantageous, with the overflow integrated into the dam body, generally resulting in substantial savings. Construction in tiers creates a stepped downstream face.

Arch-Gravity Dams

Also known as Spanish dams, these dams resist gravity partially by transmitting the load to the foundation and partially by transmitting the load through an arch shape. This dual effect reduces the volume of concrete required. The slope usually varies in the range of 1 (Vertical) : 0.6 – 0.7 (Horizontal).

Buttress Dams

Advantages

• Utilize the bearing capacity of the concrete under the foundation surface.
• Uplift pressures are small compared to solid concrete dams.
• Reduced volume under thermal effects.

Disadvantages

• Large formwork area, making them less competitive due to labor-intensive construction compared to other mechanized procedures.

Arch Dams

Characterized by upstream curvature, which contributes to their strength. The natural shape of the arch holds water in the reservoir. Structurally, they work as a horizontal arch, transmitting a portion of the load to the abutments, and also as a bracket built into the valley, especially in closed U-shaped valleys. In closed V-shaped valleys, the arch effect is more significant.

Arch dams are more efficient than gravity or buttress dams, significantly reducing the required concrete volume due to their thinner profile. They are suitable for narrow valleys with strong bedrock.

Classification

against the risk of the dam, two types of tributaries to the reservoir avenues: Avenida project: Maximum avenue that should be considered for sizing the spillway , drain bodies and structures of power dissipation, so that they work. Avenida extreme: Most avenue that the dam can withstand. Scenario assumes a limit to which the dam may be subjected without causing it to break, while accepting smaller margins of safety. Category A 1000 project and extreme 5000-10000, Category B project, 1000-5000 500 extreme Category C100 project and extreme 1000-500

GRAVITY DAMS: Resist all drawing water push the dead weight. Transmit the entire load to the foundation. Suitable for rock closed transmitted not load bearing capacity to temper the sealing is achieved by the impermeability of the material, but is not complete and the water flowing through the pore pressure of the fluids that fill the pores of the factory and land works by decreasing the effective pressures between the solid particles of such a drain is a hole through which filtered water is collected and leads to a drain. Its mission is to eliminate or at least reduce the pore pressure downstream thereof. This will reduce the uplift. The display of drains can be matched to the galleries visited the dam to facilitate maintenance screen drains should be placed as close to the upstream face screen shots are made once the dam to cut off seepage fissures in the rocks. Galleries of service used to perform maintenance work auscultation and functional boards: Due to the heat of the setting and subsequent shrinkage of concrete, it is necessary to run the dam body by alternating blocks. The unions are called together. Juntas Longitudinal axis parallel to the transverse seals prey: Perpendicular to the axis of dam construction joints: they tend to be horizontal between tiers or between blocks and are due to the construction process. A1 vacuum reservoir shall be taken to the combination of the demands of the dead weight and temperature variations. A2 full reservoir shall be taken to the combination of the demands of the self-weight, buoyancy, pore pressure, pressure of the landfills, push the ice or waves caused by wind and temperature variations. The buoyancy and pore pressure are the highest level corresponding to the normal reservoir. B11 The seismic shocks caused by, linked to the solicitations of the situation considered in A1. A2 B21 status ineffective if the drains. B22 caused by seismic shocks, coupled with the stresses considered in the A2 state. Assumed pore pressures are not affected by such shocks. Thrust may be dispensed ice or waves produced by the wind, in his case. B23 A2 Status Full-elevation on the level expected in the reservoir, including wave action extraordinary. Assumed pore pressures are not affected by over-elevation of the reservoir. Thrust may be dispensed from the ice. DAMS OF GRAVITY: compacted concrete Economically, have the overflow in the body of the dam means, generally, very substantial savings through tiers construction makes the downstream face this all the steps formed by ARCO GRAVITY DAMS Dams gravity arch dam also known as Spanish. Resist gravity part transmitting the load to the foundation. Resist the effect of load transmitting arc temper. This dual effect reduces the volume of concrete slope The amount usually varies in the range: 1 (V): 0.6 – 0.7 (H)DAMS buttress ADVANTAGES: Take the bearing capacity of concrete to be under the surface of foundation uplift pressures are small encomparación with hormigón.Son macizas.Reduce volume under thermal effects. DISADVANTAGES: There is a large area of what today formwork in day recently competetiva by requiring labor intensive compared to other much more constructive procedure shall mechanized machinery. They have a considerable arch dams upstream curvature, which depends on its strength. The natural shape of the arch (curve) holds water in the reservoir. Structurally u work as horizontal arc, transmitting a portion of the load to the abutments and also works as a bracket built in the valley, especially in closed U-shaped In closed form of V is more important to the arch effect. In structural terms arch dam is more efficient than gravity dams or buttress, to significantly reduce the volume of concrete required, they are thinner. They are suitable for closed stirrups close to bedrock. Arch dams are generally classified as thin, medium and heavy depending on the ratio of the width of the base (b) and height (h): Slim: b / h 0.3