Geophysical Characterization of Flood Protection Barriers: West Bank, Louisiana, USA.
Speaker: Dr. Juan Lorenzo
Associate Professor, Departmnet of Geology and Geophysics
LSU, Baton Rouge, LA.
Biography:
Abstract:
To date, construction of flood protection barriers has been achieved with traditional geotechnical characterizations of the subsurface. However, maintenance and monitoring of these same structures requires a novel approach. Whereas subsurface geotechnical data exist, they are only collected at widely spaced intervals, often hundreds of feet apart, far exceeding the scale of the weak links in the levee system.
I propose a comprehensive, geo-scientific methodology for the maintenance and evaluation of a coastal flood protection system, that integrates seismic, electrical resistivity and engineering log data. I use as a test case, a distressed portion of the V-levee of Marrero, Louisiana, USA.
Many mechanisms for failure such as, liquefaction or underseepage, can be attributed to a lack of understanding of the strength and permeability of the embankment and its soil foundation. Inherent uncertainties in the engineering analyses and unexpected variability in the foundation soils can be checked independently through geophysical methods.
Based on preliminary field tests across the distressed levee, transmission tomographic analyses across its crest display sensitivity to changes in average shear wave velocities. The shear velocity (and hence shear strength) in the material used to build the artificial levee crest is twofold greater (~20 m/s) than the natural soils in the levee foundation. Relatively lower shear strength appears under the visibly distressed portion of the levee, than at two other apparently non-distressed locations along the levee.