Condition Assessment of Levees, U.S. Section of the International Boundary and Water Commission. Report 5: Flood Simulation Study of Retamal Levee, Lower Rio Grande Valley, Texas, Using Seismic and Electrical Geophysical Models
Rept. no. 5
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS GEOTECHNICAL AND STRUCTURES LAB
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In November 2004, a team from the U.S. Army Engineer Research and Development Center conducted a ponding test on a reach of the Retamal levee in the Lower Rio Grande Valley to simulate performance of the levee during a flood event. The work was performed for and with the assistance of the International Boundary and Water Commission, U.S. Section, on a levee reach with a significant number of surface cracks. Surface cracking of the levee was caused primarily by drought conditions as they affected expansive clay soils where total annual rainfall, in south Texas, was less than 20 in. 0.5 m for several years between 1998 and 2003. Geophysical monitoring of the levee provided important information about levee performance during a maximum flood event and measured changes in moisture in clay soils in the levee. Various types of state-of-the-art electrical and seismic methods were appraised to monitor seepage caused by floodwater ponded against the levee. Seismic methods are especially attractive for levee screening, as velocity data from shear and body waves correlate directly to engineering properties that measure shear strength of soils. Seismic data indicated the higher rainfall in 2004 positively affected the core of the levee. Measurable increases in the seismic velocity of both body and shear waves were observed in 2004, compared with conditions in 2003, near the end of the drought period. Velocity values prior to the flood test in 2003 were much lower, likely caused by a levee core that was internally cracked and caused slower P- and S-wave velocities.
- Geology, Geochemistry and Mineralogy
- Civil Engineering
- Environmental Health and Safety