Slope Instability of the Earthen Levee in Boston, UK: Numerical Simulation and Sensor Data Analysis

The paper presents a slope stability analysis for a heterogeneous earthen levee in Boston, UK, which is prone to occasional slope failures under tidal loads. Dynamic behavior of the levee under tidal fluctuations was simulated using a finite element model of variably saturated linear elastic perfectly plastic soil. Hydraulic conductivities of the soil strata have been calibrated according to piezometers readings, in order to obtain correct range of hydraulic loads in tidal mode. Finite element simulation was complemented with series of limit equilibrium analyses. Stability analyses have shown that slope failure occurs with the development of a circular slip surface located in the soft clay layer. Both models (FEM and LEM) confirm that the least stable hydraulic condition is the combination of the minimum river levels at low tide with the maximal saturation of soil layers. FEM results indicate that in winter time the levee is almost at its limit state, at the margin of safety (strength reduction factor values are 1.03 and 1.04 for the low-tide and high-tide phases, respectively); these results agree with real-life observations. The stability analyses have been implemented as real-time components integrated into the UrbanFlood early warning system for flood protection

Energy efficient wireless sensor network protocols for monitoring and prognostics of large scale systems

In this work, energy-efficient protocols for wireless sensor networks (WSN) with applications to prognostics are investigated. Both analytical methods and verification are shown for the proposed methods via either hardware experiments or simulation. This work is presented in five papers. Energy-efficiency methods for WSN include distributed algorithms for i) optimal routing, ii) adaptive scheduling, iii) adaptive transmission power and data-rate control --Abstract, page iv

Applications of MASW and MHVSR Techniques for Infrastructure Evaluation with a Focus on the Effects of Different Transformation Techniques and Near-field Effects on Derived Dispersion Data

This dissertation is aimed at understanding two aspects of active surface wave methods to improve the accuracy and reliability of this method. These include (1) the performance of four common wavefield transformation methods for the multichannel analysis of surface wave (MASW) data processing and (2) near-field effects. Toward this end, extensive field measurements were conducted considering different factors affecting these two topics. The MASW and microtremor horizontal to vertical spectral ratio (MHVSR) were then employed to examine their efficiency for infrastructure health monitoring. Regarding the performance of the four common transformation techniques, it was observed that for sites with a very shallow and highly variable bedrock topography with a high-frequency point of curvature (\u3e20 Hz), the Phase Shift (PS) method leads to a very poor-resolution dispersion image compared to other transformation methods. For sites with a velocity reversal, the Slant Stack (p) method fails to resolve the dispersion image for frequencies associated with layers located below the velocity reversal layer. Overall, the cylindrical frequency domain beamformer (FDBF-cylindrical) method was determined to be the best method under most site conditions. This method allows for a stable, high-resolution dispersion image for different sites and noise conditions over a wide range of frequencies, and it mitigates the near-field effects by modeling a cylindrical wavefield. However, the FDBF-cylindrical was observed to be dominated by higher modes at complex sites. Therefore, the best practice is to use more than one transformation method (FDBF-cylindrical and FK methods) to enhance the data quality. Regarding the near-field effects for active surface wave methods, it was observed that near-field effects are independent of surface wave type (Rayleigh and Love) and depth to impedance contrast. For sites with a very shallow impedance contrast, the FDBF-cylindrical transformation technique outperforms others in terms of dispersion resolution by significantly mitigating near-field effects. It is also revealed that source type is an important parameter, influencing the normalized array center distance criteria required to mitigate near-field effects. The best practical criteria for near-field mitigation include a normalized array center distance of 1.0 or greater for low-output impulsive sources such as a sledgehammer and a normalized array center distance of 0.5 for high-output harmonic sources such as a vibroseis. These criteria should not be violated when using a limited number of source offsets (≤2). But, if the multiple source offset approach (≥3 source offsets) is used where some of the source offsets meet the criteria, the near-field criteria can be violated for other source offsets. Additionally, it is recommended to use the multiple source offset approach along with the FDBF-cylindrical for data processing to mitigate near-field effects. For health monitoring of earthen hydraulic infrastructures, MASW was determined to be effective for detecting weak zones of such structures. In this regard, it is very important to use the reference shear wave velocity profiles to avoid misinterpretation of the results. Additionally, the grid pattern MHVSR method was determined to very effective for landslide evaluations for sites with shallow and complex bedrock topography, where bedrock is a key feature in the slope stability model

Evaluating the Use of sUAS-Derived Imagery for Monitoring Flood Protection Infrastructure

In the US there are approximately 33,000 miles of levees. This includes 14,500 miles of levee systems associated with US Army Corps of Engineers programs and approximately 15,000 miles from other state and federal agencies. More than 14 million people live behind levees and associated flood prevention infrastructure. Monitoring and risk assessment are an on-going process, especially during times of flood conditions. The city of New Orleans was heavily impacted by Hurricane Katrina in 2005 by storm surges and intense rainfall. The impact of the hurricane was substantial enough to cause levee failure and I-wall toppling where many of the levees were breached and waters flooded the city. Subsidence and increasing population are likely to make flooding events more frequent and costly. As new technologies emerge, monitoring and risk assessment can benefit to increase community resiliency. In this research, I investigate the use of the structure from motion photogrammetric method to monitor positional changes in invariant objects such as levees, specifically, I-walls. This method uses conventional digital images from multiple view locations and angles by either a moving aerial platform or terrestrial photography. Using parallel coded software and accompanying hardware, 3D point clouds, digital surface models and orthophotos can be created. By providing comparisons of similar processing workflows with a variety of imaging acquisition criteria using commercially available unmanned aerial systems (UAS), we created multiple image sets of a simulated I-wall at various flight elevations, look angles, and effective overlap. The comparisons can be used for sensor selection and mission planning to improve the quality of the final product

Mapping and evaluating the condition of artificial levees

Artificial levees along alluvial rivers are major components of flood risk mitigation. This is especially true in the case of Hungary, where more than one-third of the country is threatened by floods and protected by an over 2940-km-long levee system. Most of the levees were built in the 19th century. Since then, several natural and anthropogenic processes, such as compaction, erosion, Etc., could contribute to these earth structures' slow but steady deformation. Meanwhile, as construction works were scarcely documented, the structure and composition of artificial levees are not well known. Therefore, the present analysis aimed to use different geophysical techniques to validate their efficiency in mapping structural differences, possible compositional deficiencies, potential defects and sections where elevation decrease and compare the compositional and structural variations of two very different levee sections along a 24 km section of the River Tisza and a 24 km section of the River Maros. Investigations were conducted by real-time kinematic GPS (RTK-GPS), Ground penetrating radar (GPR), Electrical Resistivity Tomography (ERT) and drillings. Onsite data acquisition was complemented with an analysis using a Persistent Scatterer Synthetic Aperture Radar (PSI) to assess general surface deformation. The higher frequency 200 MHz GPR data have shown that levee structures can significantly vary even in a few km on sections with the same construction history. Based on electrical resistivity tomography results with a precise analysis of grain size and their related physical parameters used for monitoring the materials of two different levee sections along the Tisza and Maros rivers, we noticed that the main components of investigated Tisza levee section are medium and fine silts, however, the situation of the investigated Maros levee section shows more variation of different materials which are fine, medium, and coarse silt, moreover, fine, medium, and coarse sand. The investigated section of the Tisza levee showed low resistivity values, indicating the fine-grained materials' conductivity. In contrast, the investigated section of the Maros levee showed high resistivity values, indicating the resistivity nature of higher grain size sediments forming this section, especially noticed on the protected side of the levee. It was possible to capture structural changes and resolving the thin layers by 1 m electrode spacing ERT profile. In turn, at a larger spacing it was possible to get information on the sedimentary base below the levee body. The selected levee section could be assessed in terms of its structure and composition and major units within the levee body and their composition could be resolved by the applied methods. In general, there is a similarity in the materials and their resistivity range which form the core of Tisza and Maros levees, however, the situation on their both sides is not the same. Regarding the analysis of different physical properties of the two levee systems like resistivity, porosity, density, water content, grain size, and saturated hydraulic conductivity, the materials of the Maros levee could be distinguished well and showed more variation when it is compared to the materials of Tisza levee. It means that the physical properties of levee materials are very important, and they are recommended when carrying out further levee investigations. From the physical properties mentioned above, it was found that some of them show a connection with resistivity except hydraulic conductivity parameter that did not show a direct connection, however the latter could exhibit the aquitard nature of Tisza levee materials and the non-aquitard nature of Maros levee materials which illustrates the difference in levee composition in terms of flood risk or flood safety. Based on height measurements, the mean elevation of the levee crown decreased by 8 cm in a 40-year time span. However, elevation decrease could reach up to 30 cm at some locations. Sections affected by structural anomalies, compositional changes, and increased surface subsidence are especially sensitive to floods when measurement results are compared to flood phenomena archives. GPR profiles showed several anomalies, including structural and compositional discontinuities and local features. They were classified into six types regarding to the flood risk; tensile cracks (enables piping, leading to levee breach or mass failure, cracks might close when the levee gets wet), remarkable changes in dielectric permittivity (enables seepage, leading to mass failure), animal burrows (enables piping, leading to levee breach or mass failure), layer deformation (results in height decrease, overtopping), paleo river channel (enables seepage below the levee, leading to water upwelling and the development of sand boils), sudden change in stratification or dipping layers (enables contour line seepage, leading to mass failure). The penetration dept

Levee Slide Detection using Synthetic Aperture Radar Magnitude and Phase

The objectives of this research are to support the development of state-of-the-art methods using remotely sensed data to detect slides or anomalies in an efficient and cost-effective manner based on the use of SAR technology. Slough or slump slides are slope failures along a levee, which leave areas of the levee vulnerable to seepage and failure during high water events. This work investigates the facility of detecting the slough slides on an earthen levee with different types of polarimetric Synthetic Aperture Radar (polSAR) imagery. The source SAR imagery is fully quad-polarimetric L-band data from the NASA Jet Propulsion Laboratory’s (JPL’s) Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR). The study area encompasses a portion of the levees of the lower Mississippi river, located in Mississippi, United States. The obtained classification results reveal that the polSAR data unsupervised classification with features extraction produces more appropriate results than the unsupervised classification with no features extraction. Obviously, supervised classification methods provide better classification results compared to the unsupervised methods. The anomaly identification is good with these results and was improved with the use of a majority filter. The classification accuracy is further improved with a morphology filter. The classification accuracy is significantly improved with the use of GLCM features. The classification results obtained for all three cases (magnitude, phase, and complex data), with classification accuracies for the complex data being higher, indicate that the use of synthetic aperture radar in combination with remote sensing imagery can effectively detect anomalies or slides on an earthen levee. For all the three samples it consistently shows that the accuracies for the complex data are higher when compared to those from the magnitude and phase data alone. The tests comparing complex data features to magnitude and phase data alone, and full complex data, and use of post-processing filter, all had very high accuracy. Hence we included more test samples to validate and distinguish results