Poking the Bear: Drilling and Sampling for Embankment Dams
URS Corp., April, 2014
Poking the Bear: Drilling and Sampling for Embankment Dams” discusses the risks, planning requirements, and best practices associated with intrusive subsurface investigations in embankment dams. While drilling and sampling are sometimes necessary to obtain site‑specific geotechnical data, they can damage the embankment by creating new seepage paths or connecting existing weak zones, particularly when drilling fluids are used. As a result, intrusive investigations should only be performed when clearly warranted, after non‑intrusive methods have been considered, and under the supervision of experienced engineers and drillers.
The article emphasizes the importance of a detailed and flexible investigation plan that defines objectives, drilling locations, methods, contingencies, and emergency response procedures. It reviews common sampling techniques and drilling methods, highlighting hollow‑stem auger drilling as the preferred method for embankment dams due to its lower risk. Guidance is provided for drilling in the core, shell, and foundation zones, with strong caution to avoid drilling in sensitive areas such as cores, cutoff trenches, and zones of known seepage. The article concludes that careful planning, method selection, and real‑time monitoring are essential to safely obtain subsurface data without compromising dam safety.
This short article was published in Vol. 2, Iss. 1 of the Western Dam Engineering Technical Note (WDETN) and describes considerations for drilling and sampling at embankment dams. The WDETN was a collaborative effort between the States of Colorado, Montana, New Mexico and Wyoming which was funded by the FEMA National Dam Safety Act Assistance to States grant program. Special thanks to URS Corporation in Denver, Colorado for authoring the article.
Revision ID: 8307
Revision Date: 02/01/2026