Geological Influences On Dam site Selection

The selection of a dam site and the type of dam to be built is a crucial decision that is influenced by a variety of factors, including topography, geology and foundation conditions, materials availability, spillway size and location, and potential for earthquakes.

Topography is a major factor in the selection of a dam site, as it can impact the type of dam that is most suitable for a particular location. For example, a narrow stream flowing between high, rocky walls may suggest a concrete overflow dam, while low, rolling plains may suggest an earthfill dam with a separate spillway. The location of the spillway is also an important consideration that is heavily influenced by the local topography.

Geology and foundation conditions also play a significant role in the selection of a dam site. The geological character and thickness of the strata that will bear the weight of the dam, as well as their inclination, permeability, and relationship to underlying strata, existing faults, and joints, all influence foundation conditions. The foundation will limit the type of dam to some extent, but will frequently be modified to account for the proposed dam's height.

The availability of materials is another important factor to consider when selecting a dam site. Soils for embankments, rock for embankments and riprap, and concrete aggregate (sand, gravel, and crushed rock) should all be available on-site or nearby. The cost-effectiveness of the dam is often determined by the availability and cost of materials.

The size and location of the spillway is also an important consideration when selecting a dam site. The spillway must be large enough to safely handle the maximum flow of water, and its location should be such that it does not pose a threat to downstream areas.

Finally, the potential for earthquakes is also a major factor to consider when selecting a dam site. Dams must be designed to withstand the forces of earthquakes, and the risk of earthquakes in a particular area must be evaluated before a dam site is selected.

In conclusion, the selection of a dam site and the type of dam to be built is a complex process that is influenced by a variety of factors. Engineers must consider topography, geology and foundation conditions, materials availability, spillway size and location, and potential for earthquakes when selecting a dam site. This will help ensure that the dam is built in the most cost-effective and safe way possible.

Geological influences on dam foundations

The selection of a dam site and the type of dam to be built is heavily influenced by the foundation conditions and geology of the area. The geological character and thickness of the strata that will bear the weight of the dam, as well as their inclination, permeability, and relationship to underlying strata, existing faults, and joints, all play a crucial role in determining the foundation conditions of a site.

There are five main types of foundation conditions: solid rock foundations, gravel foundations, silt or fine sand foundations, clay foundations, and non-uniform foundations. Each type of foundation has its own set of characteristics and impacts the selection of a dam type and site.

Solid rock foundations are considered the best foundation, and the overall cost of materials will be the decisive factor. The removal of disintegrated rock, as well as the grouting of edges and fractures, will frequently be necessary.

Gravel foundations, if thoroughly compacted, are suitable for 'earthfill', 'rockfill', and low 'concrete gravity dams'. However, because gravel foundations are usually prone to high rates of water percolation, particular efforts must be made to establish adequate water cutoffs or seals.

Silt or fine sand foundations, if properly engineered, can be used to sustain low concrete gravity dams and earthfill dams, but they are not suited for rockfill dams. The main issues are settlement, high percolation losses, and erosion protection of the foundation at the downstream toe.

Clay foundations can be used to support earthfill dams. However, because the dam may settle significantly if the clay is unconsolidated and the moisture content is excessive, clay foundations are generally not suitable for the building of concrete gravity dams and should not be utilized for rockfill dams.

Non-uniform foundations can be a combination of rock and soft soil. Special design characteristics can help to reduce such undesirable conditions.

In addition, it is important to note that the geology of the site, including the presence of faults, joints, and the orientation of strata, can also have a significant impact on the stability of a proposed dam and must be taken into account during the site selection process. A thorough understanding of the foundation conditions and geology of a site is crucial in determining the most suitable dam type and location, as well as ensuring the safety and stability of the structure.