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March Luncheon Meeting

Title: March Luncheon Meeting

Location: The Petroleum Club

Speaker: Juan M. Lorenzo, LSU Department of Geology and Geophysics

Description:“Geophysical Monitoring of Artificial Earthen Levees”

Start Time: 11:30

Date: 2012-03-21


Abstract:

A growing societal need exists for scientific involvement in the study of flood protection systems, addressable by near-surface seismic methods. Both deep- and near-surface hydrogeologic processes can contribute to the structural failure of artificial flood protection embankments, dikes, or artificial levees. Recently, seismic geophysical methods have attempted to develop a proxy for engineering shear strength, by mapping changes in the transmission velocity of shear waves through artificial levees. In the absence of electromagnetic methods, Vp/Vs ratios can be used as good indicators of variations in the fluid (water, and air or gas) saturation. A distressed section of an artificial earthen levee, suitable for seismic investigation, lies ~15 km south of New Orleans, Louisiana. A 100-m section of the crest shows continuous cracks which are as much as 10 cm wide, and 30 cm deep at their northern end. Between September 2007 and February 2008, we collected horizontally polarized shear and compressional wave data in pseudo-walk-away tests focusing on the natural soils (upper 30 m) of the protected (west) flank of the earthen levee 30 m away from the crest. Two profiles lie parallel and on either flank of the damaged levee crest and, for reference, two profiles sample undamaged portions of the protected levee flank. Cone-Penetration Tests (CPT) are spaced at 300

m intervals along the levee crest. In the first 30 m (~100 feet) of sediment below the lower delta plain of

the Greater New Orleans area, a complex and dynamic interaction of freshwater and marine sedimentary environments has juxtaposed a diverse set of facies. From the integration of Vp and Vs velocity maps (from body and Love waves), surface facies maps, and laboratory-derived physical properties we interpret greater soil saturation on the protected side of the levee, adjacent to crestal cracks. Subsurface fluvial-deltaic facies are too variable to be predictable from physical properties at widely-spaced CPT sites alone. Future preventive, monitoring of flood-protection barriers stand to benefit from integration of geophysical profiles, calibrated to geotechnical information at point locations and integrated with geological and topographic information.


Bio:

Juan Lorenzo received a license in geology from the University of Barcelona in 1983, M.A. and M.Phil. degrees from Columbia University in 1986 and 1987, respectively, and his Ph.D. in marine seismology from Columbia University in 1991. From 1990-1992, he was a research fellow studying marine geophysics at Flinders University in South Australia. Since 1993, he has been a member of the faculty of the LSU department of Geology. In 2001, he served as a Fulbright Research/Teaching Scholar at the University of Chile. He is currently a member of the American Geophysical Union, Society of Exploration Geophysicists, American Association of Petroleum Geologists, Geological Society of America, Environmental and Engineering Geophysical Society, Southeastern Geophysical Society, and New Orleans Geological Society. Since 1993, he has served on the editorial board of Geo-Marine Letters. His current research includes geophysical monitoring of levees, alternative techniques for hydraulic fracturing monitoring to maximize safe

recovery of shale gas resources, and real-time integration of diverse data for surveillance, history-matching, and optimization.


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