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Geosynthetics have been extensively used in pavement systems, either by placing the geosynthetic at the interface between the base and subbase layers or at the interface between the subbase and subgrade layers or within the unbound base course layer to enhance the performance of roadways under repeated traffic and environmental loads. Gaining a better understanding on the geosynthetic and soil-geosynthetic interaction properties along various directions is important for geosynthetics that are subjected to multi-directional loads. Previous studies have investigated the effect of geosynthetic orientation on the unconfined tensile properties of biaxial and triangualr geogrids, whether by using numerical software or by using analytical analysis. However, the effect of geosynthetic orientation on the soil-geosynthetic interaction properties has not extensively been studied. Furthremore, properties of geotextiles have also not extensively been studied along various directions. The objective of this research is to gain a better understanding of the impact of the geosynthetic orientation on the geosynthetic and soil-geosynthetic interaction properties. Two types of test were used to achieve the objective of this research: (1) Wide-width tensile tests, which were used to investigate the impact of geosynthetic orientation on the geosynthetic properties, and (2) Soil-geosynthetic interaction tests, which were used to study the impact of geosynthetic orientation on the soil-geosynthetic interaction properties. Three types of geosynthetics that have similar mass per unit area were used in this study. This included: a triangular geogrid, a biaxial geogrid, and a woven geotextile. Geosynthetic and soil-geosynthetic interaction properties were evaluated for each geosynthetic along various directions. Variation of these properties were also compared between the three products tested. Effect of various components of the experimental setup and the test design on the findings were also evaluated. Evaluation of the results obtained from the wide-width tensile tests indicated that the ultimate tensile strength and tensile stiffness of the geogrid with triangular aperture shapes, were comparatively uniform along all tested directions. However, the ultimate tensile strength and tensile stiffness of the woven geotextile and the geogrid with rectangular aperture shapes, were highly dependent on the direction of tensile load. When the tensile load was applied along the machine or the cross-machine directions, the ultimate tensile strength and tensile stiffness of the woven geotextile and the biaxial geogrid were noticeably high. However, when the tensile load was applied along other directions (i.e., 30˚, 45˚, and 60˚), the ultimate tensile strength and tensile stiffness were comparatively low. Evaluation of the results obtained from the soil-geosynthetic interaction tests indicated that the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) of the triangular geogrid were relatively uniform along all tested directions. However, the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) of the woven geotextile and the biaxial geogrid were highly dependent on the direction of tensile load. When the pullout load was applied along the machine or the cross-machine directions, the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) were found to be comparatively high. However, when the pullout load was applied along other directions (i.e., 30˚, 45˚, and 60˚), the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) were found to be comparatively low. Overall, findings from this study indicate that the triangular geogrid tested in this study provided an isotropic in-plane behavior both in-isolation and under confinement of soil. However, the in-isolation and under confinement responses of the biaxial geogrid and the woven geotextile evaluated in this study were found to be highly anisotropic. Specifically, although the biaxial geogrid and the woven geotextile were found to have high mechanical properties in the machine and cross-machine directions, their properties along other directions were found to be comparatively low.

Geosynthetics have been extensively used in pavement systems, either by placing the geosynthetic at the interface between the base and subbase layers or at the interface between the subbase and subgrade layers or within the unbound base course layer to enhance the performance of roadways under repeated traffic and environmental loads. Gaining a better understanding on the geosynthetic and soil-geosynthetic interaction properties along various directions is important for geosynthetics that are subjected to multi-directional loads. Previous studies have investigated the effect of geosynthetic orientation on the unconfined tensile properties of biaxial and triangualr geogrids, whether by using numerical software or by using analytical analysis. However, the effect of geosynthetic orientation on the soil-geosynthetic interaction properties has not extensively been studied. Furthremore, properties of geotextiles have also not extensively been studied along various directions. The objective of this research is to gain a better understanding of the impact of the geosynthetic orientation on the geosynthetic and soil-geosynthetic interaction properties. Two types of test were used to achieve the objective of this research: (1) Wide-width tensile tests, which were used to investigate the impact of geosynthetic orientation on the geosynthetic properties, and (2) Soil-geosynthetic interaction tests, which were used to study the impact of geosynthetic orientation on the soil-geosynthetic interaction properties. Three types of geosynthetics that have similar mass per unit area were used in this study. This included: a triangular geogrid, a biaxial geogrid, and a woven geotextile. Geosynthetic and soil-geosynthetic interaction properties were evaluated for each geosynthetic along various directions. Variation of these properties were also compared between the three products tested. Effect of various components of the experimental setup and the test design on the findings were also evaluated. Evaluation of the results obtained from the wide-width tensile tests indicated that the ultimate tensile strength and tensile stiffness of the geogrid with triangular aperture shapes, were comparatively uniform along all tested directions. However, the ultimate tensile strength and tensile stiffness of the woven geotextile and the geogrid with rectangular aperture shapes, were highly dependent on the direction of tensile load. When the tensile load was applied along the machine or the cross-machine directions, the ultimate tensile strength and tensile stiffness of the woven geotextile and the biaxial geogrid were noticeably high. However, when the tensile load was applied along other directions (i.e., 30˚, 45˚, and 60˚), the ultimate tensile strength and tensile stiffness were comparatively low. Evaluation of the results obtained from the soil-geosynthetic interaction tests indicated that the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) of the triangular geogrid were relatively uniform along all tested directions. However, the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) of the woven geotextile and the biaxial geogrid were highly dependent on the direction of tensile load. When the pullout load was applied along the machine or the cross-machine directions, the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) were found to be comparatively high. However, when the pullout load was applied along other directions (i.e., 30˚, 45˚, and 60˚), the ultimate pullout resistance and the stiffness of the soil-geosynthetic composite (KSGC) were found to be comparatively low. Overall, findings from this study indicate that the triangular geogrid tested in this study provided an isotropic in-plane behavior both in-isolation and under confinement of soil. However, the in-isolation and under confinement responses of the biaxial geogrid and the woven geotextile evaluated in this study were found to be highly anisotropic. Specifically, although the biaxial geogrid and the woven geotextile were found to have high mechanical properties in the machine and cross-machine directions, their properties along other directions were found to be comparatively low.

Structural health monitoring (SHM) and performance assessment are increasingly integrated to modern civil engineering projects in order to prevent and mitigate their catastrophic premature failures. Significant advancements in sensor and communication technologies during the last decades have boosted research on SHM and revolutionized its traditional and low-tech techniques. Inherent variability and uncertainties in soils arising from different sources (e.g. data insufficiency) pose significant challenges to the design of geosystems (e.g. geosynthetically-modified structures), but the increasing trend in using SHM and performance evaluation techniques could offer substantial help in counterbalancing the design uncertainties and to identify the impending failure of high-risk geosystems. Strain gauges, optical fibers and extensometers are current technologies to measure strains in geosynthetics where the sensing is achieved by attaching these devices to a geosynthetic layer in desirable positions. However, these devices require complex and expensive data acquisition systems to collect information. Also, strain gauges attached to a reinforcement material need to be calibrated against global strains from crosshead displacements in in-isolation tensile tests. However, the resulting calibration factors are typically not accurate when the reinforcement layer is embedded in soil due to the local stiffening effect of the bonding assembly, difference in the in-soil mechanical properties and other complications such as soil arching. During the last few years, a novel technique has been under development at the University of Oklahoma based on the strain sensitivity of polymer nanocomposites to measure the tensile strain in modified geosynthetics without the need for conventional instrumentation. In this technique, electrically-conductive fillers are used to induce conductivity in geosynthetics in order to produce sensor-enabled geosynthetics (SEG). The electrical conductivity of a SEG product with a prescribed concentration of a conductive filler is highly sensitive to the applied strain, affording the product the self-sensing function. As part of this long-term study to develop SEG materials, an interdisciplinary study was carried out as described in this dissertation to develop sensor-enabled geogrids (SEGG) through laboratory experiments and molecular-scale simulations. The study yielded several formulations and production processes in the laboratory to fabricate nanocomposites that would exhibit adequate mechanical and strain-sensitive electrical properties for SEGG applications. Molecular dynamics and Monte Carlo simulations were used to gain insight into the laboratory results on a more fundamental level. The molecular dynamics simulations were carried out to study the mechanical properties of the composites whereas Monte Carlo simulations were used to examine their electrical conductivity (i.e. percolation) behavior. Results showed that, contingent upon further development and addressing practical issues such as durability and protective measures for field installation, the SEGG technology holds promise to offer a practical and cost-effective alternative to the existing technologies for performance-monitoring of a wide range of geotechnical structures during and after construction.

Increasing quantities of dredged material (DM) from navigation waterways have led to a growing need to find alternative methods of disposal. Using this material in earthwork construction is a very attractive avenue, but poses concern of quality from a geotechnical standpoint. By blending DM with granular materials like industrial steel slag fines (SSF), studies have showed that the geotechnical properties of the mixture are greatly enhanced. If these materials can be proven to be competitive for use in earthwork construction, they would pose as an economically viable alternative, and would obviate the need for the relatively expensive conventional granular backfill. The scope of this project entailed the characterization of pullout interaction of SSF-DM blends in different proportions with Tensar uniaxial geogrids to determine an optimal combination for usage in earthwork construction. The media used for testing included the individual SSF and DM materials, and the 80/20, 50/50 and 20/80 blends mixed based on dry unit weights of the individual components. The SSF media comprised of particles smaller than 3/8 in. and classified as SW, while the DM was classified OH soil. Two Tensar uniaxial geogrids UX1400 and UX1700 were undertaken for the study. Pullout tests were conducted and performances of all the blends are compared with each geogrid at various normal pressures. Pullout loads and interaction coefficients give an idea of the quality of the interaction, and are studied in this thesis. Also, various variables that could potentially affect the pullout interaction are identified and investigated. Results show remarkably high pullout resistances for the 100% SSF and 80/20 SSF/DM media, and high interaction coefficients indicating excellent pullout interaction, even better than conventional sands. It was also clear that the dredged material exhibits very poor pullout interaction with geogrids. The 50/50 and the 20/80 SSF/DM media were significantly lower than the 80/20 SSF/DM blend in terms of quality of pullout interaction, but still higher than the 100% DM. The results observed with the 80/20 SSF/DM blend show that it is a suitable backfill material and also poses to be a very competitive and cost-effective alternative to be used in earthwork construction.

Increasing quantities of dredged material (DM) from navigation waterways have led to a growing need to find alternative methods of disposal. Using this material in earthwork construction is a very attractive avenue, but poses concern of quality from a geotechnical standpoint. By blending DM with granular materials like industrial steel slag fines (SSF), studies have showed that the geotechnical properties of the mixture are greatly enhanced. If these materials can be proven to be competitive for use in earthwork construction, they would pose as an economically viable alternative, and would obviate the need for the relatively expensive conventional granular backfill. The scope of this project entailed the characterization of pullout interaction of SSF-DM blends in different proportions with Tensar uniaxial geogrids to determine an optimal combination for usage in earthwork construction. The media used for testing included the individual SSF and DM materials, and the 80/20, 50/50 and 20/80 blends mixed based on dry unit weights of the individual components. The SSF media comprised of particles smaller than 3/8 in. and classified as SW, while the DM was classified OH soil. Two Tensar uniaxial geogrids UX1400 and UX1700 were undertaken for the study. Pullout tests were conducted and performances of all the blends are compared with each geogrid at various normal pressures. Pullout loads and interaction coefficients give an idea of the quality of the interaction, and are studied in this thesis. Also, various variables that could potentially affect the pullout interaction are identified and investigated. Results show remarkably high pullout resistances for the 100% SSF and 80/20 SSF/DM media, and high interaction coefficients indicating excellent pullout interaction, even better than conventional sands. It was also clear that the dredged material exhibits very poor pullout interaction with geogrids. The 50/50 and the 20/80 SSF/DM media were significantly lower than the 80/20 SSF/DM blend in terms of quality of pullout interaction, but still higher than the 100% DM. The results observed with the 80/20 SSF/DM blend show that it is a suitable backfill material and also poses to be a very competitive and cost-effective alternative to be used in earthwork construction.

With the ever increasing need for MSE walls, the study of the interaction between soil and geosynthetics has become increasingly relevant. New concepts are constantly being researched, including the use of industrial byproducts as alternative backfill materials. The idea that byproduct material could somehow be a suitable fill for these MSE walls may spark new opportunities. One such byproduct being researched is dredged material. The suitability of dredged material as a backfill would not only contribute to lower construction costs, but would also benefit local confined disposal facilities looking to reduce their already overflowing dredged material accumulation. This thesis further considers the use of dredged material by evaluating its interface shear strength with uniaxial geogrids. A series of laboratory pullout tests were conducted using two types of uniaxial geogrids (UX1400 and UX1700) embedded in three different soil types (Monterey Sand and two different dredged materials). The laboratory results are used to examine the effect on the coefficient of interaction of the various parameters governing the pullout resistance. The results of this study show that: (1) the presence of adhesion to characterize the soil-reinforcement interface shear strength causes a decrease in the coefficient of interaction with increasing normal stress, (2) the reinforcement length of the geogrid was found not to affect the coefficient of interaction; provided that boundary effects are minimized, (3) the dredged material, tested wet of optimum, showed a response consistent with an undrained behavior, which produced pullout resistances significantly lower than that of the Monterey Sand, (4) the coefficient of interaction for the UX1700 was comparatively higher than that for the UX1400; however the differences obtained when testing Monterey Sand were similar to those obtained when testing the dredged materials.

With the ever increasing need for MSE walls, the study of the interaction between soil and geosynthetics has become increasingly relevant. New concepts are constantly being researched, including the use of industrial byproducts as alternative backfill materials. The idea that byproduct material could somehow be a suitable fill for these MSE walls may spark new opportunities. One such byproduct being researched is dredged material. The suitability of dredged material as a backfill would not only contribute to lower construction costs, but would also benefit local confined disposal facilities looking to reduce their already overflowing dredged material accumulation. This thesis further considers the use of dredged material by evaluating its interface shear strength with uniaxial geogrids. A series of laboratory pullout tests were conducted using two types of uniaxial geogrids (UX1400 and UX1700) embedded in three different soil types (Monterey Sand and two different dredged materials). The laboratory results are used to examine the effect on the coefficient of interaction of the various parameters governing the pullout resistance. The results of this study show that: (1) the presence of adhesion to characterize the soil-reinforcement interface shear strength causes a decrease in the coefficient of interaction with increasing normal stress, (2) the reinforcement length of the geogrid was found not to affect the coefficient of interaction; provided that boundary effects are minimized, (3) the dredged material, tested wet of optimum, showed a response consistent with an undrained behavior, which produced pullout resistances significantly lower than that of the Monterey Sand, (4) the coefficient of interaction for the UX1700 was comparatively higher than that for the UX1400; however the differences obtained when testing Monterey Sand were similar to those obtained when testing the dredged materials.

Geogrids are polymer-based products which are commonly used to reinforce soil walls, steep slopes and roadway bases. Inclusion of geogrids as aggregate base reinforcement, with proper installation, has been shown to result in increased stiffness and service life of flexible pavements. It also results in reduced distress and deformations, improved performance and hence, reduced repair and maintenance costs of pavements. The relationship between the in-isolation and in-aggregate properties of a geogrid depends on several factors including the geogrid and aggregate properties, their frictional and interlocking interaction mechanisms and the overburden pressure.

Loaded wheel tester (LWT) is a common testing equipment usually used to test the permanent deformation and moisture susceptibility of asphalt mixtures by applying moving wheel loads on asphalt mixture specimens. It has been widely used in the United States since 1980s and practically each Department of Transportation or highway agency owns one or more LWT(s). Compared to other testing methods for pavement materials, LWT features movable wheel loads that allow more realistic situations existing on the actual pavement to be simulated in the laboratory. Due to its potential of creating a condition of repetitive loading, the concept of using LWT for characterizing the properties of pavement materials were promoted through four innovative or modified tests in this study. (1)   The first test focuses on evaluating the effect of geogrids in reinforcing pavement base courses. In this test, a base course specimen compacted in a testing box with or without geogrids reinforced was tested under cyclic loading provided by LWT. The results showed that LWT test was able to characterize the improvement of the pavement base courses with geogrids reinforcement. In addition, the results from this study were repeatable and generally in agreement with the results from another independent study conducted by the University of Kansas with similar testing method and base materials. (2)   A simple and efficient abrasion test was developed for characterizing the abrasion resistance of pervious concrete utilizing LWT. According to the abrading mechanisms for pervious concrete, some modifications were made to the loading system of LWT to achieve better simulations of the spalling/raveling actions on pervious concrete pavements. By comparing the results from LWT abrasion tests to Cantabro abrasion tests, LWT abrasion test was proved effective to differentiate the abrasion resistances for various pervious concretes. (3)   Two innovative LWT tests were developed for characterizing the viscoelastic and fatigue properties of asphalt mixtures in this study. In the test, asphalt beam specimens are subjected to the cyclic loads supplied by the moving wheels of LWT, and the tensile deformations of the beam specimens are measured by the LVDTs mounted on the bottom. According to the stress and strain, the parameters associated to the viscoelastic and fatigue properties of the asphalt mixture can be obtained through theoretical analyses. In order to validate the concepts associated with the above mentioned tests, corresponding conventional tests have also been conducted to the same materials in the study. According to the comparisons between the conventional and the LWT tests, the LWT tests proposed in this study provided satisfactory repeatability and efficiency.

Experimental and analytical investigations were performed to evaluate the comparative performance of pavements with and without geosynthetic stabilization. This was accomplished by the testing of a total of 18 pavement sections which could be classified into four different types: one which was constructed without geosynthetics and which served as a control, and three which were stabilized with one of two geotextiles or a geogrid. The pavement sections were constructed to model a typical secondary road in Virginia which is constructed over a silty sand subgrade material. Loading of the pavement sections was accomplished through the use of a computer-controlled pneumatic system which delivered 80 lb/in2 (552 kPa) through a rigid plate at a frequency of approximately one-half Hertz. The resulting displacement of the pavement surface was monitored by an array of linear variable displacement transducers (LVDTs). The performance of each pavement section was evaluated using the American Association of State Highway and Transportation Officials (AASHTO) flexible pavement design method. Models based on empirical and mechanistic relationships were considered. A theoretical pavement section was also analyzed to assess the influence of the stiffness of a wearing course layer. An economic study was performed to assess the potential cost benefit of geosynthetic stabilization and recommendations have been made for additional research.