Evaluation of soil-reinforcement composite interaction in geosynthetic-reinforced soil structures

Soil reinforcement has become a well-established technology, providing alternatives to an increasingly large number of critical geotechnical structures. While significant advances have been made to characterize the soil-reinforcement interaction of individual reinforcement layers, field evidence has been collected that suggests unaccounted benefits in structures where the vertical spacing between reinforcements is comparatively small. The nature of the complex interactions that may develop between contiguous reinforcement layers, possibly leading to a “composite” behavior of the reinforced soil mass, requires full characterization. The degree of interaction between adjacent reinforcement layers is expected to impact, perhaps significantly, the mechanical response of the reinforced soil mass. The added benefits from interaction among reinforcement layers would be particularly relevant for critical structures, such as reinforced soil bridge abutments and piers, reinforced soil pile platforms, and reinforced soil foundations. Accordingly, this study aims at assessing the effect of geosynthetic reinforcements on the behavior of the surrounding soil, contiguous reinforcements, and the geosynthetic-reinforced soil mass at large. The findings of this study on the behavior of soil-reinforcement interaction is expected to lead to practical implications such as the selection of the reinforcement vertical spacing in geosynthetic-reinforced soil (GRS) structures. The specific objectives of this research are to (1) evaluate mechanisms involved in soil-reinforcement interaction, (2) identify and characterize the shear zone of influence surrounding a reinforcement layer under tension, (3) evaluate the interaction that develops between a reinforcement and its neighboring reinforcement layers, and (4) understand and quantify the potential benefits of closely-spaced reinforcements in GRS structures. Significant information was initially gained by reevaluating data collected from other research studies in order to assess soil-reinforcement interaction with focus on the impact of reinforcement vertical spacing on GRS structures. Specifically, a detailed evaluation of data sources was conducted, including actual experimental and field monitoring data. The data sources reevaluated in this dissertation include (1) evaluation of the performance of large-scale experimental GRS structures, (2) analysis of soil arching in GRS structures, (3) evaluation of the performance of GRS structures using geotechnical centrifuge, and (4) assessment of the performance of the Founders/Meadows GRS bridge abutments. A state-of-the-art device was developed as part of this research to comprehensively assess the soil-reinforcement composite interaction under both working stress and failure conditions. The new equipment was able to assess the mechanical behavior of a geosynthetic-reinforced soil mass considering varying reinforcement vertical spacings. In addition, it allowed investigating the interface shear stress transfer mechanisms. The device provided suitable measurements of the strains developed in both actively tensioned and the adjacent reinforcement layers. It allowed direct visualization of the kinematic response of soil particles adjacent to the geosynthetic reinforcement layers, which facilitated evaluation of the soil displacement field via digital image analysis. Evaluation of the soil displacement field allowed quantification of the extent of the zone of shear influence around a tensioned reinforcement layer. Finally, the device allowed monitoring of dilatancy within the reinforced soil mass, providing additional insight into the effect of reinforcement vertical spacing on the reinforced soil mass. A comprehensive testing program was conducted using the newly developed experimental device. The testing program was tailored to evaluate the following aspects: (1) test repeatability; (2) effect of reinforced soil confinement on the soil-reinforcement composite interaction behavior; (3) effect of reinforcement vertical spacing on the soil-reinforcement composite interaction behavior; (4) effect of reinforcement properties on the soil-reinforcement composite interaction behavior; (5) effect of boundary type on the soil-reinforcement composite interaction behavior; and (6) effect of backfill properties on the soil-reinforcement composite interaction behavior. Analysis of the experimental results revealed that the existence of the zone of shear influence and its extent can be directly related to the interaction between contiguous reinforcement layers. In particular, for the uniform gravel evaluated in this study, the zone of shear measured from the soil-reinforcement interface ranged from 0.10 to 0.30 m for the normal stress range involved in this study. It was concluded that reducing the vertical spacing between reinforcement layers in a GRS mass increases the strain compatibility between the reinforcement layers and the soil mass in between.Civil, Architectural, and Environmental Engineerin

Toward Smart Moving Target Defense for Linux Container Resiliency

This paper presents ESCAPE, an informed moving target defense mechanism for cloud containers. ESCAPE models the interaction between attackers and their target containers as a "predator searching for a prey" search game. Live migration of Linux-containers (prey) is used to avoid attacks (predator) and failures. The entire process is guided by a novel host-based behavior-monitoring system that seamlessly monitors containers for indications of intrusions and attacks. To evaluate ESCAPE effectiveness, we simulated the attack avoidance process based on a mathematical model mimicking the prey-vs-predator search game. Simulation results show high container survival probabilities with minimal added overhead.Comment: Published version is available on IEEE Xplore at http://ieeexplore.ieee.org/document/779685

Efficient ECG Compression and QRS Detection for E-Health Applications

Current medical screening and diagnostic procedures have shifted toward recording longer electrocardiogram (ECG) signals, which have traditionally been processed on personal computers (PCs) with high-speed multi-core processors and efficient memory processing. Battery-driven devices are now more commonly used for the same purpose and thus exploring highly efficient, low-power alternatives for local ECG signal collection and processing is essential for efficient and convenient clinical use. Several ECG compression methods have been reported in the current literature with limited discussion on the performance of the compressed and the reconstructed ECG signals in terms of the QRS complex detection accuracy. This paper proposes and evaluates different compression methods based not only on the compression ratio (CR) and percentage root-mean-square difference (PRD), but also based on the accuracy of QRS detection. In this paper, we have developed a lossy method (Methods III) and compared them to the most current lossless and lossy ECG compression methods (Method I and Method II, respectively). The proposed lossy compression method (Method III) achieves CR of 4.5×, PRD of 0.53, as well as an overall sensitivity of 99.78% and positive predictivity of 99.92% are achieved (when coupled with an existing QRS detection algorithm) on the MIT-BIH Arrhythmia database and an overall sensitivity of 99.90% and positive predictivity of 99.84% on the QT database.This work was made possible by NPRP grant #7-684-1-127 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.Scopu

Cooperative Access in Cognitive Radio Networks: Stable Throughput and Delay Tradeoffs

In this paper, we study and analyze fundamental throughput-delay tradeoffs in cooperative multiple access for cognitive radio systems. We focus on the class of randomized cooperative policies, whereby the secondary user (SU) serves either the queue of its own data or the queue of the primary user (PU) relayed data with certain service probabilities. The proposed policy opens room for trading the PU delay for enhanced SU delay. Towards this objective, stability conditions for the queues involved in the system are derived. Furthermore, a moment generating function approach is employed to derive closed-form expressions for the average delay encountered by the packets of both users. Results reveal that cooperation expands the stable throughput region of the system and significantly reduces the delay at both users. Moreover, we quantify the gain obtained in terms of the SU delay under the proposed policy, over conventional relaying that gives strict priority to the relay queue.Comment: accepted for publication in IEEE 12th Intl. Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOpt), 201

Variation of surface properties of ceramic and composite nanostructures and their measurements by a novel approach using perichromic dyes

TiO2 as a model photocatalyst is gaining great interest due to good activity, stability, low toxicity and cost-effectiveness. The rapid recombination between the photogenerated electrons and the holes on the TiO2 surface can be diminished by using carbon-TiO2 composites, especially Graphene (G) and Graphene Oxide (GO), which improve the photocatalytic activity of TiO2 and stability under UV-visible light illumination. The determination of surface properties including surface acidity, polarity and surface area of photocatalysts allows the control and enhancement in the photocatalytic efficiency. This study aims at investigating the surface properties of TiO2-G and TiO2-GO nanocomposites using independent techniques, correlating these surface properties and photocatalytic activity and studying the effect of particle size and the amount of G and GO on these surface properties. TiO2 nanoparticles of different sizes were prepared using sol-gel methodology and varying the rate of hydrolysis of the TiO2 precursor. The as-prepared TiO2 nanoparticles were used to prepare TiO2-G and TiO2-GO nanocomposites by mixing followed by sonication and stirring. The variables in the prepared nanocomposites were the percentage of the added G or GO together with the different TiO2 particle size. Characterization of the formed nanocomposites and the blank samples was performed by using different techniques. The surface acidity was measured using perichromic dyes and NH3-TPD; both measurements are independent. Surface polarity and polarizability were investigated using perichromic dyes to study their impact on the photocatalytic activity. Textural properties were investigated by measuring the surface area and average pore diameter. The structural characteristics of the samples were evaluated using FTIR, Raman and XRD. DRS-UV was employed to measure the band gap energy change with the addition of G or GO. The photocatalytic degradation of methylene blue (MB) dye, as a model water pollutant, was used to evaluate the photocatalytic activity of the samples. The characterization results indicated that two methods of preparation gave two average sizes of 436 ±59 nm and 251 ±32 nm for the samples denoted TL and TS which corresponds to large particle size TiO2 and small particle size TiO2, respectively. Addition of G and GO affected the structure, surface properties and photocatalytic activity of the sample. The results for the photocatalytic activity of the prepared samples, exhibited superior activity over the unmodified TiO2 and the rate enhancement ranged from 9.2 to 69.2% for TS, and 18.8 to 237.5% for TL, showing the clear advantage of using nanocomposites as photocatalysts for pollutants. Photocatalytic activity of the samples is dependent on many factors such as surface acidity, surface area and, to a much lesser extent, the change in band gap energy and the overall effect is a complex combination of all these factors. The formation of Ti-O-C chemical bonds in the samples is evidenced by the Raman results and the addition of G or GO has no effect on the crystal structure of the sample as shown in XRD results. The increase in overall surface acidity in most samples is believed to be primarily due to Brønsted acidity as Lewis acidity is generally lower than the blank in most samples. However, possible stacking of G and GO at higher concentrations resulted in the decrease in overall acidity with the increase in G or GO contents in some of the samples. Surface polarizability, which measures primarily the van der Waals surface interactions, increased with the increase in G content as would be expected due to the hydrophobic nature of G. Further investigations are needed, however, to extend the use of perichromic probes for determination of surface polarizability of solid surfaces. The overall surface acidity of the TL containing samples is generally higher than the TS samples due to higher degree of cross-linking. In conclusion, TiO2-G and TiO2-GO nanocomposites prepared by mixing and sonication were studied for the effects of changing TiO2 particle size, and of the presence and amount of G and GO. It was found that smaller particle size and the presence of G or GO improved the photocatalytic activity of the samples through the change in sample surface properties. Increasing the amount of G or GO in the samples led to limitations in the enhancement of catalytic activity. This is believed to be primarily due to possible blockage of the photocatalytic active sites on the surface of TiO2