GEOPHYSICAL SIGNATURE OF COMPROMISED ZONES WITHIN EARTHEN EMBANKMENTS AND LEVEES
Hydraulic Engineering Research
2012 Annual Report
1a.Objectives (from AD-416):
The proposed research objective is to further develop geophysical tools and technologies to assess the integrity and monitoring of earth dams and levees.
1b.Approach (from AD-416):
This research will focus on three ground-based geophysical techniques: 1. Seismic refraction tomography, 2. electrical resistivity tomography, and 3. passive seismic monitoring, all optimized for rapid dam and levee assessment. The tomography technologies described in this proposal will not require ground penetration, but will employ sensors placed on the surface of the dam or levee. NCPA laser Doppler vibrometry (LDV) research could allow these techniques to be configured in a stand-off, non-contact configuration for more rapid measurements in the future. The seismic and electrical methods proposed would be considered as advanced screening tools capable of delineating and classifying the degree of mechanical integrity of a levee and/or its foundation. These methods would be used as part of a systematic approach and implemented based upon evidence from visual inspection but before the use of traditional boring programs. The passive seismic monitoring technology would be deployed on compromised dams and sections of levees, which require immediate remediation or are classified as highly hazardous. The established relationships between geophysical signatures, erodibility, and standard Proctor test will allow for the incorporation of geophysical instrumentation to collect data for quality control during the construction of future dams and levees.
During this project, several geophysical field tests have been conducted on constructed earthen embankments using electrical resistivity and acoustics methods for mapping internal flaws. The testing has been conducted at different times of the year and with water loading and unloading on the upstream side of the earthen embankments. The embankments were also tested to failure with internal erosion events while mapping with geophysical measurements. The testing has resulted in internal mappings of the embankments, validating the applicability of these methods for identifying changes in material properties within the embankments both spatially and with time. Laboratory bench scale testing was also completed to relate erosion characteristic, and electrical resistivity and acoustic measurements of soil materials.