Seismic refraction tomography of a small earth dam

Abstract

Over the past 50 years there were nearly 11,000 flood control dams constructed by the United States Department of Agriculture (USDA) nationwide in 2,000 watersheds (USBR, 1987). The failure of these earth dams is associated with erosion, seepage, piping, slope failures, and slides. Precursory evidence for certain failures can be identified by visual inspection; however, others are not so easily detected. Seismic imaging may provide unique and valuable information about the subsurface to assist in the evaluation of the integrity of an earth dam. In this presentation, results from a field study carried out on Drewery Lake Dam in the Upper Yocona River watershed to determine the feasibility of using seismic refraction tomography for imaging earthen dams is discussed. Attributes in the refraction tomograms are correlated with the location of the drainage pipe and the excavated surface given in the as‐built plans indicating that seismic refraction tomography does have sensitivity to the internal structure of a dam. This study also suggests that the construction practices for earthen dams result in seismically uniform structures. A uniform background is very advantageous if seismic tomography is to be used to detect zones of internal weakness.