Variability in Earthen Levee Seismic Response Due to Time-History Selection

In seismic slope stability analyses the single most important input parameter is the ground motion. Time-history selection is a challenging engineering problem since the variability in ground motion characterization is in part due to the complexity of the mechanisms that result in a seismic event taking place and the path and soil conditions from the origin of the seismic event to the location of interest. In this study, the effect of key ground motion parameters to the dynamic response of earthen levees is investigated. Specifically, the effect on the induced cyclic shear stress ratio (CSR) and/or seismically induced Newmark-type, permanent displacements (U) for prescribed sliding surfaces is discussed. Results were obtained by performing 2-D equivalent linear finite element dynamic analyses for a total of 1,000 ground motions. The mean period, Tm, of the ground motion, and the peak ground velocity, PGV, are among the parameters identified by this study as being good indices for seismic levee response. Identifying the parameters that correlate best with the variability in response will allow the formulation of time-history selection criteria for the seismic response of earthen levees

Accuracy Analysis Comparison of Supervised Classification Methods for Anomaly Detection on Levees Using SAR Imagery

This paper analyzes the use of a synthetic aperture radar (SAR) imagery to support levee condition assessment by detecting potential slide areas in an efficient and cost-effective manner. Levees are prone to a failure in the form of internal erosion within the earthen structure and landslides (also called slough or slump slides). If not repaired, slough slides may lead to levee failures. In this paper, we compare the accuracy of the supervised classification methods minimum distance (MD) using Euclidean and Mahalanobis distance, support vector machine (SVM), and maximum likelihood (ML), using SAR technology to detect slough slides on earthen levees. In this work, the effectiveness of the algorithms was demonstrated using quad-polarimetric L-band SAR imagery from the NASA Jet Propulsion Laboratory’s (JPL’s) uninhabited aerial vehicle synthetic aperture radar (UAVSAR). The study area is a section of the lower Mississippi River valley in the Southern USA, where earthen flood control levees are maintained by the US Army Corps of Engineers

Effect of River Levee with Geosynthetic-Reinforced Soil against Overflow Erosion and Infiltration

Overflows from huge floods have caused levee breaches in a great number of places, including Japan. To prevent such destruction and thereby increase the resistance of armored levees to overflow erosion, in this study, we examined the performances of Geosynthetic-Reinforced Soil (GRS) levees against overflow erosion under various conditions, such as reinforcement, back slopes, and geo-grid layers. In addition, we investigated the effect of geo-grid layers on the infiltration of levees. The model tests revealed that 1) with scour protection in front of the toe of the back slope, the GRS levee exhibits much higher resistance against overflow erosion than the armored levee; 2) the armored levee with a steep back slope (= 1:0.5) collapsed faster than that with a normal slope (= 1:2). However, the GRS levee with a steep back slope of 1:0.5 maintained high resistance against overflow erosion after the target time. 3) The GRS levee with partial and full reinforcements had a comparably high resistance against overflow erosion. 4) The GRS levee using a small-sized geo-grid maintained a high residual ratio of the cross-sectional area over a long period. 5) The infiltration discharge of the GRS levee was lesser than that of the levee with no reinforcement due to the reduction in infiltration erosion in the GRS levee. These facts suggest that the GRS levee with partial reinforcement can be applied to the reinforcement of existing levees, and appropriately sized geo-grid layers should be selected

A Supervised Classification Method for Levee Slide Detection Using Complex Synthetic Aperture Radar Imagery

The dynamics of surface and sub-surface water events can lead to slope instability, resulting in anomalies such as slough slides on earthen levees. Early detection of these anomalies by a remote sensing approach could save time versus direct assessment. We have implemented a supervised Mahalanobis distance classification algorithm for the detection of slough slides on levees using complex polarimetric Synthetic Aperture Radar (polSAR) data. The classifier output was followed by a spatial majority filter post-processing step that improved the accuracy. The effectiveness of the algorithm is demonstrated using fully quad-polarimetric L-band Synthetic Aperture Radar (SAR) imagery from the NASA Jet Propulsion Laboratory’s (JPL’s) Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR). The study area is a section of the lower Mississippi River valley in the southern USA. Slide detection accuracy of up to 98 percent was achieved, although the number of available slides examples was small

A customized resistivity system for monitoring saturation and seepage in earthen levees: Installation and validation

This work is based on the assumption that a resistivity meter can effectively monitor water saturation in earth levees and can be used as a warning system when saturation exceeds the expected seasonal maxima. We performed time-lapse ERT measurements to assess the capability of this method to detect areas where seepage is critical. These measurements were also very useful to design a prototype monitoring system with remarkable savings by customizing the specifications according to field observations. The prototype consists of a remotely controlled low-power resistivity meter with a spread of 48 stainless steel 20 Ã 20 cm plate electrodes buried at half-meter depth. We deployed the newly-designed permanent monitoring system on a critical levee segment. A weather station and an ultrasonic water level sensor were also installed in order to analyse the correlation of resistivity with temperature, rainfalls and water level seasonal variations. The preliminary analysis of the monitoring data shows that the resistivity maps follow a very reasonable trend related with the saturation/drying cycle of the levee caused by the seasonal variations of the water level in the irrigation channel. Sharp water level changes cause delayed and smooth resistivity variations. Rainfalls and, to a lesser extent, temperature seem to have an influence on the collected data but effects are apparently negligible beyond 1 m depth. The system is currently operating and results are continuously monitored

Identifying the Vulnerability of Earthen Levees to Slump Slides using Geotechnical and Geomorphological Parameters

The main goal of this research is to investigate vulnerability of levees to future slump slides. In the first part, polarimetric synthetic aperture radar (PolSAR) imagery is used as input in an automated classification system for characterizing areas on the levee having anomalies. In addition, a set of in-situ soil data is collected to provide detailed soil properties over the study area. In-situ soil properties of different classes characterized by the classifier are analyzed to determine how similarities between different areas. The second part, a database including of 34 slump slides that occurred in the lower Mississippi River levee system over a period of two years is used. The impacts of rainfall as well as several spatial geometrical and geomorphological variables (including channel width, river sinuosity index, riverbank erosion, channel shape condition and distance to river) are analyzed and tested for significance and used for developing a logistic regression model

Modeling compound effects of earthquakes and flooding on the failure probability of earthen levees

Earthen levees are crucial components of a nation\u27s flood protection system. However, in some regions, these levees face the unique challenge of being subjected to both floods and earthquakes throughout their lifespan, an aspect that is relatively unexplored in the existing literature. The primary aim of this research is to examine earthquakes\u27 and floods\u27 effects on earthen levee failures. Using numerical simulations, the seepage, slope stability, and liquefaction potential of an earthen levee were modeled by considering compound of different floods and earthquakes scenarios. Elkhorn Levee in Sacramento, CA, was used as a representative case study for the simulations. The probability of levee failure and the extent of the breach caused by compound flood-earthquake scenarios are further determined by Fault Tree Method. The findings provide a practical approach to analyzing levee systems under multi-hazard conditions and enhancing levee resilience

Transient Seepage in a Variably Saturated Levee: Laboratory Testing, Field Monitoring and Numerical Modeling

Several hydraulic loadings impose earthen levees to time-dependent variably saturated seepage conditions. The main objective of this study is to improve the analysis of levees under transient seepage with the use of unsaturated soil mechanics. An extensive set of laboratory testing, field monitoring and numerical modeling are performed to analyze a silty sand setback levee located near Seattle, WA. In-situ data obtained from field monitoring are used to monitor suction and effective stress within the levee’s embankment and foundation over the past two years. Soil samples taken from the site are used to perform index, water retention, and unsaturated multi-stage triaxial tests in the laboratory. A finite element model of transient seepage under saturated-unsaturated conditions is then developed and calibrated to reasonably match the field data. The results highlight the need to consider unsaturated soil mechanics along with climatic variables and soil-atmosphere interaction when analyzing levees under transient seepage conditions