Thesis--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 58-59).

Master of Science / Civil Engineering / Stacey Tucker / Recent climate changes may affect the stability of our infrastructure in many ways. This study investigated the effects of fine-grained soil temperature on erosion rate. If climate change is shown to affect the erodibility of soils the impacts must be identified to monitor the stability of existing infrastructure, improve design of levees and structures founded in erosive environments, and to prevent sediment loss and stream meanders. Fine-grained soil erosion is complicated by the dynamic linkage of multiple parameters, including physical, biological and geochemical properties. This study held constant all parameters that influence fine-grained soil erodibility while only varying soil temperature in order to study the effects it has on erodibility. This study also confirmed previous findings that water temperature affects soil erodibility. The main objective of this study was to investigate the effects of fine-grained soil temperature on erosion rate. This study also instrumented a turbidity sensor to reliably map soil erosion. Based on this research, the conclusion was made that an increase in soil temperature increases soil erosion rate. The turbidity sensor was a valuable tool for comparing soil erosion. Future studies should investigate the effects soil temperatures below room temperature, the magnitude of temperature increase or decrease, and the effects of cyclic heating and cooling on fine grained soil erodibility.

The United States contains an estimated 100,000 miles (160000 km) of levees in which erosion related issues are the top priorities. Proper documentation of overtopping induced erosion is a complicated issue involving the collection and analysis of timesensitive field data and personal observations. This thesis is a study of the performance of the Midwest Levee system during the 2008 flooding events. The goal of the Midwest Levee investigation was to gather and analyze perishable data in an effort to provide a comprehensive overview at each breach location. To predict how a site will perform during a particular flood event, there are three main inputs: the flood conditions, the site conditions, and the soil properties. Site geometry and imperfections can greatly affect the performance of a levee system. Any low spots or potential seepage paths can concentrate the flow and be detrimental to the levee. The vegetative cover is the single most important condition at a site. As seen in the Brevator case, vegetative armor can prevent failure of a levee comprised of less resistant soils subjected to long periods of overtopping. Recommended grasses include: Switchgrass, Smooth Brome, Reed Canarygrass, and Tall Fescue. It is also recommended that grasses are kept at least 0.5 m tall during the flood season and to limit the presence of trees to 10 m beyond the levee toe. The erosion resistance of the materials comprising the levee is also important. From the correlations in this study, it was determined that erodibility is influenced by grain size, relative compaction, clay content, and activity. Devices like the Torvane and Pocket Erodometer can also be used to get a quick field estimate of erosion. While these correlations and field devices give insight into an erodibility value, they are no substitute for site specific analysis with laboratory equipment such as the Erosion Function Apparatus. Soil behavior is highly nonlinear and the entire erosion function is needed to get an accurate measure of the erodibility of a soil. By combining these properties in an erosion matrix, a prediction of whether a site will withstand a given flood event can be made.

Doctor of Philosophy / Department of Civil Engineering / Stacey E. Tucker-Kulesza / Surface soil erosion is a widespread problem that impacts the natural and built environment. Many disciplines, such as hydrology, soil science, agriculture, and geotechnical engineering, have investigated soil erosion. Although empirical equations to predict soil erosion exist, they are typically inaccurate, so several devices have been developed to quantify the erodibility of soil. The erosion function apparatus (EFA) was developed to predict the erosion potential of soil for evaluating bridge scour; however, it has been used for several other geotechnical applications. The main disadvantages of the EFA are that it is unable to directly measure the shear stress, it remains operator dependent, and it is time consuming as a standard test requires at least eight hours. Moreover, as erosion occurs, it affects the water quality and makes it difficult to observe the soil sample surface during the test, affecting the operator judgement. The research objective of this project is to instrument the EFA to address the limitations of the device. A stereo-photogrammetry system was developed to measure the soil surface roughness following an EFA test and reduce operator dependency. Turbidity sensors were added to provide a secondary measurement of erosion. The newly instrumented EFA was used to develop a new methodology for interpreting erosion results. Lastly, the new methodology and instrumentation were used to explore the influence of natural and engineered soil properties on soil erosion.

AL’érosion interne est l’une des principales causes d'instabilité des ouvrages de retenue hydrauliques tels que les digues, les levées et les barrages. Cette pathologie peut mener à la ruine de l’ouvrage avec des pertes humaines et d’importants dégâts matériels. Ce travail de thèse est consacré à la caractérisation de la suffusion dans les sols homogènes et hétérogènes, et participe aux études menées dans le cadre du projet national ERINOH (ERosion INterne des Ouvrages Hydrauliques). Les essais menés sur l’EFA ont été effectués sur des échantillons homogènes constitués de sables et de fines (Kaolinite, Illite ou Silt) reconstitués au laboratoire. Les résultats ont montré l’importance du type et du pourcentage des fines sur la résistance à l’érosion. Par la suite, les résultats de ces essais ont été comparés aux résultats obtenus avec les mêmes matériaux réalisés à l’IFFSTAR (Paris) avec le dispositif d’érosion de trou HET. Les résultats des classifications selon les deux dispositifs placent chaque matériau testé dans des catégories similaires. Les deux approches expérimentales (EFA et HET) peuvent donc être complémentaires pour la classification des sols vis-à-vis de l’érosion interne. L’utilisation de l’EFA se révèle être plus appropriée pour des sols à faible proportion de fines qui ne peuvent pas être testés au HET. Les essais réalisés en colonne ont été effectués sur deux types de matériaux : des sols homogènes et des sols hétérogènes. Les essais sur sols homogènes ont été menés sur des matériaux constitués de sables et de fines (Argiles et Limon) à différentes proportions. Les essais ont montré également l’influence du type et du pourcentage de fines sur l’initiation et la cinétique de l’érosion. Quant aux essais sur sols hétérogènes, ils sont répartis en trois catégories : les essais sur sol bi-couches, les essais sur sol ségrégé et les essais sur sol naturel. Les essais sur sol bi-couhes ont servi à montrer l’influence sur la suffusion d’une hétérogénéité géométrique créée par une discontinuité granulométrique sur l’érosion. Ces essais ont montré aussi qu’un sol ségrégé pouvait dans certaines conditions être légèrement plus résistant à l’érosion. Dans ces essais, l’étude de l’évolution de la perméabilité en cours d’essai et l'analyse granulométrique après essai montrent une redistribution granulaire au sein de l’échantillon, qui peut mener à une meilleure résistance à la suffusion. Les essais sur le sol naturel (graves du Rhin) ont montré que ce dernier présente une résistance à la suffusion sous les sollicitations hydrauliques, en raison de la propriété d’auto-filtration. Les mesures de pressions le long de l’échantillon ont permis de mettre en évidence la variation des gradients hydrauliques locaux, paramètres indirects de redistribution de fines dans l’échantillon avec un colmatage potentiel. / AInternal erosion is one of main causes of instabilities of hydraulic retaining structures such as dykes, levees and dams. This problem can lead to the collapse of the structure with considerable material damage and sometimes human losses. This study is devoted to characterisation of suffusion in homogeneous and heterogeneous soil. It also participates to other studies performed in the framework of the the national project ERINOH (INternal ERosion in Hydraulic Structures). Tests using the device EFA (Erosion Function Apparatus) were performed on homogeneous samples made of sand and fines (Kaolinite, Illite ou Silt) prepared in the laboratory. The results showed the importance of the type and the percentage of fines on the erosion resistance. Thereafter, these results were compared to other results obtained from similar samples and performed at IFFSTAR (Paris) using HET (Hole Erosion Test) device. This comparison showed important differences on estimating the hydraulic shear stress. Nevertheless, classification results for both devices place tested samples in similar categories. These two devices (EFA and HET) can be complementary in soil classification against internal erosion. The EFA showed that it can perform tests on samples containing lower percentage of fines which cannot be tested on the HET device. Tests on erosion columns were performed on two different kinds of soils : homogeneous et heterogeneous soils. Homogeneous soils were made of sand and fines (clays and Silt) at different fines contents in the whole composition. The results showed the importance of the type and the percentage of fines on the initiation and evolusion of the suffusion. Tests performed on heterogeneous soils were splitted into three different categories : Two-layers sample tests, segregated sample tests and tests carried out with natural soils. Test using two-layers sample showed the influence of a geometrical heterogeneity created by granulometric discontinuity on suffusion. Segregation tests showed that under fixed conditions segregated sample can be slightly more resistant against internal erosion. The observation of permeability and post-test grain size analysis showed redistribution of soil particles that can lead to better resistance against suffusion. Test performed on natural soil (Rhine gravels) showed substancial resistance against suffusion under hydraulic load due to auto-filtration properties. Pressure measurments along the sample showed the variation of local hydraulic gradients, indirect parameters of fines redistribution in the sample with partial clogging.