Erosion Study of New Orleans Levee Soils Subjected to Plunging Water.

摘要

When the unprecedented Hurricane Katrina blew through New Orleans, it caused many failures in the Hurricane Protection System (HPS) in several different ways; foundation instability in weak clay soils, intense seepage and uplift pressure in sand foundation, overtopping of canal water and subsequent erosion of levee soils. Geoteclmical, structural, and material solutions might be enforced to enhance the integrity and resiliency of these infrastructures. However, this study focuses only on geotechnical solutions by evaluating erosion-related levee performance and providing better design criteria for erosion resistant levee soils.;To simulate the field overtopping and erosion situation in the laboratory, the UMETB (University of Mississippi Erosion Test Bed) was fabricated, calibrated, and used for testing. Erosion tests were performed in the UMETB on soils taken from one of the levee quarry sites in New Orleans and commercially manufactured Kaolin mixtures. These tests evaluated the erosion resistance of soils of varying clay percentage, degree of compaction, and water content. In addition, the reinforced levee soil conditions were evaluated by conducting erosion tests with soils treated with POSS, Vetiver, geotextiles, and cement.;Moreover, this study developed a non-constant erosion rate coefficient, analyzed field erosion depths using the excess shear stress concept for plunging water condition, and compared the developed erosion depths with the observed erosion depths in the New Orleans area during Hurricane Katrina.;From the tests, it was concluded that the non-dispersive soils should have a high degree of compaction in order to have a higher erosion resistance, while dispersive soils should have both a high degree of compaction and low permeability in order to reduce water penetration causing soil dispersion. Also, it was observed that a critical clay content exists, above which erosion resistance steeply decreases.;Erosion resistance showed improvement using reinforcements, and the soils reinforced with 5% of cement powder by weight showed the highest amount of erosion resistance. Analyses results showed that the idea of a non-constant erosion rate coefficient that was previously assumed as constant provided better agreements with measured data than that of a constant erosion rate coefficient.