Evaluation Of Geosynthetics Reinforcement In Flexible Pavement Structures Using Accelerated Pavement Testing
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Evaluation of Geosynthetic Reinforced Flexible Pavement Systems Using Two Pavement Test Facilities
| Author | : Steven W. Perkins |
| Publisher | : |
| Total Pages | : 120 |
| Release | : 2002 |
| Genre | : Geosynthetics |
| ISBN | : |
Montana State University has previously completed experimental test section, numerical modeling and design model development projects for the Montana Department of Transportation. Test section work has led to a fundamental understanding of mechanisms by which geosynthetics provide reinforcement when placed in the aggregate layer of flexible pavements. Finite element numerical models have relied upon this knowledge as their basis while design models derived from these numerical models have been calibrated against results from test sections. The test sections used for the development of these models were limited by the number of subgrade types, geosynthetic types and loading type employed. This project was initiated to provide additional test section data to better define the influence of traffic loading type and geosynthetic reinforcement type. The loading provided to the test sections forming the basis of the models described above consisted of a cyclic load applied to a stationary plate. In this project, four full scale test sections were constructed and loaded with a heavy vehicle simulator located at the U.S. Army Corps of Engineers facility in Hanover, NH. The four test sections used three geosynthetics identical to those used in previous test sections and pavement layer materials and thickness similar to previous sections. Additional test sections were constructed in the pavement test box used in previous studies to examine the influence of base aggregate type, base course thickness reduction levels and reinforcement type. A rounded pit run aggregate was used in test sections to evaluate the influence of geosynthetic aggregate shear interaction parameters on reinforcement benefit. The 1993 AASHTO Design Guide was used to backcalculate the base course thickness reduction from previous test section results where a traffic benefit ratio (extension of life) was known. Sections were built to this base course thickness reduction to see if equivalent life to an unreinforced section was obtained. Finally, six different geosynthetic products were used in test sections to evaluate the influence of reinforcement type on pavement performance.
Accelerated Load Testing of Geosynthetic Base Reinforced Unpaved and Pavement Test Sections
| Author | : Murad Yusuf Abu-Farsakh |
| Publisher | : |
| Total Pages | : 107 |
| Release | : 2019 |
| Genre | : TECHNOLOGY & ENGINEERING |
| ISBN | : |
This research study aims at evaluating the benefits of using geosynthetics to reinforce/stabilize base aggregate layer/subgrade in pavements under repeated loading test conditions. For this purpose, a total of six 80-ft. long and 13 ft. wide full-scale test lane sections were constructed, among which two sections were reinforced by one or two layers of triaxial geogrids, two sections were reinforced by one layer of high strength woven geotextile with different base layer thickness, and the remaining two sections were the control sections. The field test sections were instrumented by a variety of sensors to measure the load- and environment-associated pavement response and performance. Two series of tests, moving wheel load tests and cyclic plate load tests, were conducted to investigate the field performance of geosynthetic reinforced/stabilized paved roads and to identify the differences in pavement response to moving wheel and cyclic plate loads. In addition, six similar test sections were constructed inside a 6.5-ft. × 6.5-ft. × 5.5-ft. test box. The test box sections were also instrumented by a variety of sensors to measure the load-associated pavement response and performance. Laboratory cyclic plate load tests were then conducted. The results of accelerated load testing on the pavement test sections demonstrate the benefits of using geosynthetics in reducing the permanent deformation in the pavement structure. The adjusted traffic benefit ratio (TBRadj) associated with geosynthetic reinforcement can be increased up to 2.12 at a rut depth of 0.75 in. for pavement constructed using 18 in. thick base layer on top of weak subgrade soil using two layers of geogrid reinforcement. The inclusion of geosynthetics results in redistributing the applied load to a wider area, thus reducing the accumulated permanent deformation within the subgrade. The benefit of geosynthetics on reducing the maximum stress on top of subgrade is more appreciable at higher load levels. It was also found that the geosynthetics placed at the base-subgrade interface was able to improve the performance of both subgrade and base layers; by placing an additional layer of geogrid at the upper one-third of the base layer, the performance of the base layer was further enhanced. While geosynthetics showed appreciable benefit on reducing the permanent deformation of the subgrade layer, it showed less effect on the resilient properties of the subgrade layer. Drainage of the base layer has important effect on the performance of pavement structures for both unreinforced and reinforced lane sections. The life-cycle cost analysis (LCCA) demonstrated the cost savings of using geosynthetics in pavement as compared to the unreinforced/untreated sections. However, compared to the 12-in. cement/lime treated subgrade with the cement stabilized base pavement section, the LCCA showed it is more cost effective to use geosynthetics for base thickness less than 12 in. (or 15 in. of unreinforced aggregate base). The cost benefit becomes close for base thickness 12 in. between using a single geosynthetic layer and a 12-in. cement/lime treated subgrade with a cement stabilized base. Moreover, the cost benefit of using double geogrid layers exceeds the cost savings of a 12-in. treated subgrade with a cement stabilized base.
A Study of Geosynthetic Reinforced Flexible Pavement System
| Author | : Ranjiv Gupta |
| Publisher | : |
| Total Pages | : 562 |
| Release | : 2009 |
| Genre | : |
| ISBN | : |
The use of geosynthetics as reinforcement for the base layer of flexible pavement systems has grown steadily over the past thirty years. In spite of the evidence that geosynthetic reinforcements can lead to improved pavement performance, the specific conditions or mechanisms that enable and govern the reinforcement are unclear, largely remaining unidentified and unmeasured. The appropriate selection of design parameters for geosynthetics is complicated by the difficulty in associating their relevant properties to the improved pavement performance. In addition, pavement structures deteriorate under the combined effects of traffic loading and environmental conditions, such as moisture changes. However, these factors have not been studied together in the evaluation of the overall performance of pavement systems. Consequently, this research focused on the assessment of the effect of geosynthetics on the pavement structural section's ability to support traffic loads and to resist environmental changes. Accordingly, the primary objectives of this research were: (i) to determine the governing mechanisms and relevant properties of geosynthetics that contribute to the enhanced performance of pavement systems; (ii) to develop appropriate analytical, laboratory and field methods that are capable of quantifying the above properties for geosynthetics; and (iii) to enable the prediction of pavement performance depending on the various types of geosynthetics used. To fulfill these three objectives, an evaluative, laboratory and field study was performed. The improved performance of pavements due to addition of geosynthetics was attributed to the ability of geosynthetics to laterally restrain the base course material, thereby providing a confinement effect to the pavement. A parameter to quantify the soil-geosynthetic interaction at low displacement magnitudes based on the solution of an analytical model for geosynthetics confined in pullout box was proposed. The pullout tests were then conducted on various geosynthetics to obtain the proposed parameter for various geosynthetics. The quantitative magnitude of the parameter value from the laboratory tests was compared with the qualitative performance observed in the field test sections. Overall, a good agreement was obtained between the laboratory and field results, thereby providing confidence in the ability of the proposed analytical model to predict the governing mechanism for geosynthetic reinforced pavements.
Evaluation of Mechanisms Governing the Stabilization of Unbound Aggregate Bases by Geogrids in Flexible Pavements
| Author | : Subramanian Sankaranarayanan |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2023 |
| Genre | : |
| ISBN | : |
The benefits of using geosynthetics to stabilize the unbound aggregate layers in flexible pavements, in terms of improvement to pavement life or potential decrease in layer thickness, have been well documented. Early research focused on developing ratios such as the traffic benefit ratio (TBR) or the layer coefficient ratio (LCR) to quantify (empirically) the benefits of including geogrids, and for their use in the design of flexible pavements with those geogrids. However, the lack of a mechanistic understanding of geogrid-stabilization and the empirical nature of this data limited their use to the geogrids and pavement materials that were used to develop them. With the proliferation of different geogrid products and pavement materials, the scope of the early research has become limited and attempts to correlate the properties of the geogrids and pavement materials to the improvement in performance of the pavement have not been successful. This study aims to further the understanding of the mechanisms involved in geogrid-stabilization and to identify the mechanistically relevant properties that contribute to this stabilization. Accelerated pavement tests are conducted, using the model mobile load simulator (MLS11), on reduced-scale pavement test sections with and without geogrids for stabilization under controlled, laboratory conditions. The performance of the pavement sections is evaluated by monitoring the deformation of the surface, the internal particle displacements (within the base), and the dynamic increase in stress (within the pavement structure) for increasing traffic volume. The deformation of the surface is obtained by profiling the surface of the pavement at regular traffic intervals using a laser profilometer, designed and built in-house for this study. A unique cost-effective displacement measuring technique is developed and implemented to obtain the horizontal displacement data of particles in the base. The data from the dense array of the particle tracking sensors is used to generate the horizontal displacement field, horizontal normal strain field and shear transfer efficiency plots in the base. The vertical stress distribution is obtained from the earth pressure cells installed within the pavement structure that are monitored for dynamic stress responses with applied traffic. The inclusion of the stabilizing geogrid resulted in reduced rut development, reduced particle displacements within the base and a wider distribution of the applied load for similar traffic volumes in the control and stabilized sections. The improvement in pavement life due to the stabilization of the base by the geogrid is quantified as the traffic benefit ratio (TBR). The TBRs are determined for seven different geogrids from the accelerated pavement tests, and correlated with the most commonly used in-isolation properties of the geogrid (geometric and tensile properties), and interaction properties of the geogrid-base aggregate composite. The TBRs are found to be best correlated to the coefficients of soil-geosynthetic composite stiffness (K [subscript SGC]) obtained from the soil-geosynthetic interaction tests
Designing with Geosynthetics
| Author | : Robert M. Koerner |
| Publisher | : |
| Total Pages | : 680 |
| Release | : 1990 |
| Genre | : Technology & Engineering |
| ISBN | : |
Geosynthetic materials have entered the mainstream in the professional arena and are no longer considered new construction material. Professionals need to keep up with the nuances of how geosynthetics work. Emphasizes design by function; overviews all types of geosynthetics, with stand-alone units on particular materials. Uses S.I. units for all problems and examples. Expands coverage of containers and tubes in the geotextile chapter. Discusses walls and slope design, including seismic analysis, in the geogrid chapter. Treats wet landfills, agricultural waste, waste stability, and dam waterproofing in the geomembrane chapter. Discusses new products and related performances in the geosynthetic clay liner chapter. Discusses new products and related behavior, including fiber reinforcement and wall drainage, in the geocomposite chapter. Adds a completely new chapter on geofoam. A useful reference for transportation, geotechnical, environmental, and hydraulics professionals and engineers.
Evaluating the Effectiveness of a Hybrid Geosynthetic Reinforcement System to Mitigate Differential Heave on Flexible Pavement Due to Expansive Subgrades
| Author | : Mir Md Tamim |
| Publisher | : |
| Total Pages | : 127 |
| Release | : 2017 |
| Genre | : Geosynthetics |
| ISBN | : |
"Transportation industries encounter substantial challenges with respect to ride quality and serviceability when they deal with expansive soils underneath roadway structures. These soils exhibit swell-shrink behavior with moisture variations, which cause surficial heaving on the pavement structure and cost billions of dollars for the maintenance of pavements. For the past four decades, a particular stretch of US-95 (Oregon line to Elephant Butte) exhibited recurrent swelling distresses due to the underlying expansive soils. Despite remedial measures that exhibited satisfactory results for most of the sections, recurrent damage still continued in few sections. Further research indicated that the problematic soils were located at a depth below 1.82 m. Conventional chemical remediation methods typically performed at a depth no greater than 0.9 to 1.2 m. To be able to address the adverse effects of this swell-shrink behavior of soil at a deeper depth, hybrid geosynthetic systems were proposed. Hybrid geosynthetic systems were successfully used to mitigate expansive soil swelling in railroad applications. Hence, this research study explored this idea of using hybrid geosynthetic reinforcement systems (geocell-geogrid combination) to mitigate differential pavement heaving resulting from underlying expansive soils. To evaluate the use of hybrid geosynthetic systems in reducing differential heaving from expansive subgrades, a large-scale box test was developed to simulate a pavement section with a base course and expansive subgrade (asphalt overlay was ignored). The surficial heaving on the base course reinforced with geocell, geogrid and hybrid geosynthetic reinforced system (HGRS) were measured over time and compared with the unreinforced case. The large-scale box test results showed that the geosynthetic systems significantly reduced the maximum surficial heave along with the differential swelling on the pavement section. HGRS exhibited better performance than geocells and geogrids. Numerical analysis using the finite element approach was conducted to study the response of other soil types not tested in the box. The numerical model was first calibrated using using the box test results and the calibrated model was used to change soil properties for two other soil types with different swelling charecteristics. In the numerical model, swelling behavior of expansive soils was simulated using material models that incorporate volumetric swelling and suction as a function of moisture content. The modulus of the unreinforced base was determined using laboratory tests while the modulus that for the reinforced sections was calibrated using large scale test data. The calibration of control model was performed by controlling the moisture percolation through subgrade."--Boise State University ScholarWorks.
Efficient Transportation and Pavement Systems: Characterization, Mechanisms, Simulation, and Modeling
| Author | : Imad L. Al-Qadi |
| Publisher | : CRC Press |
| Total Pages | : 924 |
| Release | : 2008-11-01 |
| Genre | : Technology & Engineering |
| ISBN | : 0203881206 |
Internationally, significant attention is given to transport sustainability including planning, design, construction, evaluation, safety and durability of the road system. The 4th International Gulf Conference on Roads: Efficient Transportation and Pavement Systems - Characterization, Mechanisms, Simulation, and Modeling, hosted by the University o
Geosynthetic Reinforcement of Flexible Pavements
| Author | : Steven W. Perkins |
| Publisher | : |
| Total Pages | : 140 |
| Release | : 1999 |
| Genre | : Roads |
| ISBN | : |
Over the course of the last 17 years, approximately 12 different studies have shown the potential for the use of geosynthetic materials (geogrids and geotextiles) as a reinforcement inclusion in the base course aggregate layer of flexible pavements. The attraction of this application lies in the possibility of reducing the thickness of the base course layer such that a roadway of equal service life results or in extending the service life of the roadway. While several existing studies have provided data that aid in describing mechanisms of reinforcement, detailed information required to understand the mechanisms by which geosynthetics reinforce flexible pavements is lacking. In the absence of this information, it has historically been difficult to create mechanistic based models that adequately describe the process. As such, efforts to establish design solutions have been based largely on empirical data and considerations. Existing design solutions have not been met with open acceptance due to their inability to predict performance for conditions other than those established in the experiments for which the solution was based. This research was undertaken to provide experimental data that could be used to further establish the mechanisms of geosynthetic reinforcement that lead to enhanced pavement performance. Subsequent work will involve the use of these data in developing numerical models and design solutions for this application. Pavement test sections have been constructed in a laboratory based pavement test facility. The facility consists of a large concrete box in which field scale pavement layers can be constructed. Loading is provided through the application of a cyclic, 40 kN load applied to a stationary plate resting on the pavement surface. The test sections have been instrumented with an extensive series of stress and strain cells. Test section variables have included geosynthetic type (two biaxial geogrid products and one woven geotextile), subgrade type and strength, placement position of the geosynthetic in the base course layer and base course layer thickness. The results have shown that the inclusion of a geosynthetic provides a significant reinforcement effect. The geosynthetic is shown to have an influence on the amount of lateral spreading that occurs in both the bottom of the base course layer and in the top of the subgrade. Reinforcement is also seen to produce a more distributed vertical stress distribution on the top of the subgrade. As a result of these effects, reinforcement limits the vertical strain developed in the base and subgrade layers, leading to less surface deformation. Given that these mechanisms result from the development of shear interaction between the base and the geosynthetic, the combination of these effects is termed a mechanism of a shear resisting interface. These effects are seen to be most significant for a soft subgrade where substantial improvement in pavement performance has been observed. Geosynthetic type, strength, stiffness and placement position are also seen to influence observed improvement.
