A dam investigation should be designed around engineering decisions, not simply around collecting borehole logs. The objective is to develop a defensible geological and geotechnical model for the embankment, foundation, abutments, and borrow sources.
The program should establish:
Boreholes should be positioned to characterize the dam axis, abutments, cutoff area, and other critical zones. Sampling and rock coring should be supplemented where appropriate by in-situ testing and permeability testing.
The depth and spacing must be adjusted to geology and dam geometry rather than applied mechanically.
Borrow materials should be evaluated for:
A material that looks suitable in a test pit may become unsuitable at production scale because of variability.
Groundwater observations should cover seasonal and operational variability where practical. Piezometric conditions are essential for both seepage and slope-stability models.
The testing program should be driven by design needs. Common tests include particle-size distribution, Atterberg limits, Proctor-type compaction, permeability, consolidation, triaxial or direct-shear strength, and rock characterization.
USACE laboratory guidance emphasizes obtaining soil properties appropriate for civil-works design. [1]
The final deliverable should not be only a collection of logs. It should include interpreted geological sections, engineering units, groundwater conditions, uncertainty zones, and design parameters with justification.
Where data are sparse, use conservative parameter ranges and identify what additional investigation would most reduce uncertainty. Investigation should be risk-informed: focus effort where an unknown could materially change the design.
Engineering note: This article is educational technical content. Final dam design, safety assessment, acceptance criteria, and construction specifications must follow the requirements of the governing jurisdiction, project-specific design criteria, qualified engineers, and applicable dam-safety regulations.