Using the HVSR, MASW, and Seismic Refraction Analysis Methods to Estimate the Subsurface Seismic Structures of Two Earth Embankment Dams

Abstract

Degradation within an earth embankment structure is often unobservable from the surface. In order to evaluate the structural integrity of earth embankment dams and levees and identify subsurface zones of weakness that may result in future failures, various geophysical methods have been proposed as effective subsurface imaging tools. This study presents the results of using the horizontal-to-vertical spectral ratio (HVSR), seismic refraction analysis, and multi-channel analysis of surface waves (MASW) methods to estimate subsurface seismic structures for two earth embankment dams located in Chestnut Hill, MA, and Franklin Falls, NH. The estimated seismic velocity structures from the seismic refraction analysis and MASW performed in this study confirm the HVSR method is able to effectively estimate depth to bedrock at sites atop earth embankments using estimated fundamental frequencies. The MASW was found to resolve a low-velocity zone in the subsurface at the Chestnut Hill reservoir embankment that the seismic refraction method was unable to image, and this low-velocity zone is required to best fit a theoretical HVSR to an observed spectrum. Furthermore, the variation and uncertainty in fundamental frequency estimation were investigated by making repeated HVSR measurements at the Chestnut Hill embankment.