Geotechnical Exploration

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A USBR geotechnical engineer collecting a soil sample. (Wikipedia)

Before any construction or design work can be completed at a potential dam site, conducting geotechnical subsurface and onsite material exploration is essential. These explorations consist of both invasive and non-invasive sampling methods. Invasive geotechnical sampling methods may include drilling boreholes and taking core samples from the overburden and bedrock within the footprint of the dam and its appurtenances, taking soil samples from open pits, or using correlative field tests. Non-invasive geotechnical sampling methods may include but are not limited to using geophysical methods involving emitting ground penetrating radar or creating mechanically induced seismic waves.

The intent of the geotechnical investigation is to characterize the foundation conditions and uncover any potential problems at the project location. Any potential problems that are identified by thorough investigation can be addressed in the design of the various features of the dam.

“The magnitude of the foundation exploration program is governed principally by the complexity of the foundation problem and the size of the project. Explorations of borrow and excavation areas should be undertaken early in the investigational program so that quantities and properties of soils and rock available for embankment construction can be determined before detailed studies of embankment sections are made”.

“Investigate site geologic and geotechnical conditions in a manner that adequately examines embankments, spillways, abutments, borrow areas, and foundations to enable adequate evaluation of all design conditions. Provide appropriate intensity and detail of these investigations for the class of dam, complexity of site geology, and the data needed for the dam design”.

Types of Destructive Exploration

The methods below are common techniques used for destructive exploration:

• Test Pitting
• Coring
• Drilling

Types of Non-Destructive Exploration

The methods below are common techniques used for non-destructive exploration:

• Geophysical
• Photogrammetry
• Site Reconnaissance

Best Practices Resources

Drilling in Earth Embankment Dams and Levees (EM 1110-1-1807) (U.S. Army Corps of Engineers)

Geophysical Exploration for Engineering and Environmental Investigations (EM 1110-1-1802) (U.S. Army Corps of Engineers)

Geology National Engineering Handbook: Chapter 2- Engineering Geologic Investigations (Natural Resources Conservation Service)

Geology National Engineering Handbook: Chapter 3- Engineering Classification of Earth Materials (Natural Resources Conservation Service)

Geology National Engineering Handbook: Chapter 4- Engineering Classification of Rock Materials (Natural Resources Conservation Service)

Geology National Engineering Handbook: Chapter 5- Engineering Geology Logging, Sampling, and Testing (Natural Resources Conservation Service)

Engineering Guidelines for the Evaluation of Hydropower Projects: Chapter 5- Geotechnical Investigations and Studies (Federal Energy Regulatory Commission)

General Design and Construction Considerations for Earth and Rock-Fill Dams (EM 1110-2-2300) (U.S. Army Corps of Engineers)

Technical Release 210-60: Earth Dams and Reservoirs (Natural Resources Conservation Service)

Trainings

On-Demand Webinar: Drilling Plans and Hazard Evaluations for Dams and Levees

On-Demand Webinar: The Practical Use of Geophysics to Assess Dam and Levee Safety

On-Demand Webinar: Field Investigations for New and Existing Dams

On-Demand Webinar: Structural Condition Assessment of Dam Facilities with Non-Destructive Evaluation Methods

Citations:

Revision ID: 3724
Revision Date: 09/17/2022