ASDSO Dam Safety Toolbox

Rock Foundations

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Construction of Pathfinder Dam's bedrock foundation.

(Image Source: National Archives and Records Administration)

Rock foundations provide a stable and durable base for the dam structure. The foundation must be capable of withstanding the applied loads, including the weight of the dam and the forces exerted by the reservoir water. They prevent excessive settlement, reducing the potential for sliding or toppling, and minimizing the risk of seepage or erosion. The design of the rock foundation aims to ensure the integrity and stability of the dam while maximizing its resilience to various external forces and geologic conditions.

Several key considerations when designing rock foundations include the strength, durability, and structural integrity of the rock mass, as well as its jointing, discontinuities, and shear strength properties. The characteristics of the rock foundation influence its response to applied loads, seismicity, and water pressures. Understanding the geologic conditions and properties of the rock foundation is crucial for selecting appropriate foundation design strategies, excavation methods, and stabilization measures.

Various assessment methods are employed in dam engineering to evaluate the behavior and stability of rock foundations. Geological mapping, geophysical surveys, and core drilling provide valuable data on the rock mass properties, such as rock type, structure, and strength. Laboratory testing, including uniaxial compression tests and point load tests, helps determine the rock mass properties and shear strength parameters. Rock mass rating systems and rock quality designation aid in assessing the stability and support capacity of the rock foundation.

The stability and resilience of the rock foundation are crucial for the overall stability and performance of the dam. A stable foundation ensures that the dam can safely resist external forces, including water pressures, seismic loads, and changes in reservoir water levels. The rock foundation also provides resistance against the potential for slope instability, uplift forces, and deformation. Proper foundation design, including excavation techniques, rock reinforcement, and grouting, are essential for maintaining the stability and integrity of the dam, minimizing the risk of failures, and ensuring the long-term resilience of the structure.

Best Practices Resources

Rock Foundations (EM 1110-1-2908), USACE

General Design and Construction Considerations for Earth and Rock-Fill Dams (EM 1110-2-2300), USACE