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Experimental Evaluation of Geocell-Reinforced Bases Under Repeated Loading

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Experimental Evaluation of Geocell-Reinforced Bases Under Repeated Loading Accepted Manuscript Experimental Evaluation of Geocell-Reinforced Bases under Repeated Loading Sanat K. Pokharel, Jie Han, Dov Leshchinsky, Robert L. Parsons PII: S1996-6814(16)30194-8 DOI: http://dx.doi.org/10.1016/j.ijprt.2017.03.007 Reference: IJPRT 82 To appear in: International Journal of Pavement Research and Technology Received Date: 9 September 2016 Revised Date: 8 March 2017 Accepted Date: 12 March 2017 Please cite this article as: S.K. Pokharel, J. Han, D. Leshchinsky, R.L. Parsons, Experimental Evaluation of Geocell- Reinforced Bases under Repeated Loading, International Journal of Pavement Research and Technology (2017), doi: http://dx.doi.org/10.1016/j.ijprt.2017.03.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Experimental Evaluation of Geocell-Reinforced Bases under Repeated Loading Sanat K. Pokharel1, Jie Han2*, Dov Leshchinsky3, and Robert L. Parsons2 1 Stratum Logics Inc., St. Albert, Alberta, T8N 7L5, Canada. Tel +17808032359; fax +17804082259; email: [email protected] 2*Civil, Environmental, and Architectural Engineering Department, the University of Kansas, Lawrence, Kansas 66045, USA. Tel +17858643714; fax +17858645631; email: [email protected] 3 Emeritus professor, Department of Civil and Environmental Engineering, the University of Delaware, Newark, DE 19719, USA. Tel +13028312446; email: [email protected] *Corresponding author. Abstract Geocells, one type of geosynthetics manufactured in a form of three-dimensional interconnected cells, have been reported to effectively provide lateral confinement to infill material to increase the modulus and bearing capacity of base courses. Most studies so far have been focused on the behavior of geocell-reinforced bases under static loading. Geocells used for pavement applications are subjected to repeated loading. Limited studies have been conducted so far to investigate the performance of geocell-reinforced bases under repeated loading. In this study, single and multiple geocell-reinforced granular bases with three types of infill materials (Kansas River sand, quarry waste, and AB-3 aggregate) were tested and compared with the unreinforced bases under repeated loading. This study experimentally investigated the effect of the geocell reinforcement on the permanent deformation and percentage elastic deformation of 1 the granular bases. The test results showed that the geocell reinforcement reduced the permanent deformation and increased the percentage elastic deformation of the granular bases. Multiple geocell-reinforced sections demonstrated even better performance as compared with single geocell-reinforced sections. Keywords: Geosynthetic reinforcement, geocells, permanent deformation, elastic deformation, repeated loading, base course. Introduction Geosynthetic reinforcement, one of the established techniques of ground improvement for over 40 years, has been developed extensively to improve the performance of both paved and unpaved roads. Geosynthetic reinforcement has been used to increase bearing capacity and modulus, reduce required base thickness, extend the service life of the pavement, reduce operational cost, and minimize maintenance requirements [1, 2]. Therefore, it is considered as a sustainable option to overcome premature pavement failure. Majority of the research on geosynthetics for pavement applications so far, has focused on planar reinforcement, such as geogrid and geotextile, and has resulted in several design methods [1, 2, 3, 4, 5]. However, the three-dimensional forms of interconnected honeycomb geosynthetic cells, known as geocells, are not that commonly used as compared with geogrids and woven geotextiles. One major reason for this situation is that theories and design methods for geocells have been lagging far behind the applications in the field [6]. The idea of cellular confinement was first developed by the United States Army Corps of Engineers in 1970s [7]. The geocells then were made of paper soaked in phenolic water resistant 2 resin. Later metallic geocells were chosen to meet the strength requirements but they proved unfeasible because of handling difficulty and high cost. Cellular structures resembling geocells were also made from geogrids forming the sides and diaphragms [8, 9]. Geocells have also been made using geogrid sheets jointed by bodkin bars (for example, Carter and Dixon [10]). Commercially available geocells are now made of high-density polyethylene (HDPE) and novel polymeric alloy (NPA). NPA geocells are explained in the sections to follow. Geocells come in different shapes and sizes; however, the most common shape of geocell is nearly circular. Geocells provide enhanced confinement effect and impart apparent cohesion [11]; increase strength [12] and resilient modulus [13, 14]; and significantly improve the load- deformation and stress distribution characteristics of poorly-graded materials [15]. The extent of bearing capacity increase is correlated with the horizontal stiffness of the cell material [16] and the hoop stresses in the geocell wall are the most significant contributing factor towards resisting loads [17]. NPA geocell-reinforcement reduces the plastic deformation and increase the percent of elastic deformation under repeated loading [18, 19]. A series of static plate load tests conducted by Pokharel et al. [20] showed that the shape of geocell layout, the stiffness and type of geocell material, and the property of infill material all played vital roles in the behavior of geocell-reinforced bases under static loading. Pokharel et al. [20] recommended a near circular shape of geocell layout as the most efficient one. Pavement failure is often caused by insufficient stiffness and strength of the pavement structure including subgrade, base, and asphalt or concrete surface, under heavy and repeated traffic loading. Al-Qadi and Hughes [21] reported an increase of the resilient moduli of aggregate layers by about two times due to the installation of geocells within an asphalt paved road construction. Field tests with industrial by-products as the infill material in the geocell over 3 a period of12-month was also found to achieve all the essential performance requirements [22]. Han et al. [23] and Thakur et al. [24] studied recycled asphalt pavement (RAP) materials used as infill materials while in the Pokharel et al. [25] study three different infill materials were used including Aggregate Base Type 3 (AB-3), quarry waste (QW), and RAP. Both studies showed the benefits of geocell reinforcement in reducing ruts if unreinforced and reinforced sections are equally compacted. Under static loading, Pokharel et al. [20] found the modulus of the single geocell-reinforced bases improved by up to two times that of the unreinforced bases while the bearing capacities of the single geocell-reinforced bases were improved by up to 2.5 times those of the unreinforced bases. Thakur et al. [24] investigated the effect of geocell confinement on the creep deformation on RAP base material and they found that the geocell confinement significantly reduced the creep deformation of the RAP base material. Although a summary of the above-mentioned past studies on geocell reinforcement confirms that the geocell can provide confinement and increase the modulus and strength of infill material, geocell-reinforced bases under repeated loading have not been well investigated. In this study, repeated load tests on single and multiple geocell-reinforced bases were carried out using three different infill materials. In addition, NPA geocells manufactured using a new manufacture technology than HDPE were used in this study. This paper presents the results of an experimental study conducted to with NPA geocells. Repeated plate load tests were carried out on unreinforced, single geocell-reinforced, and multiple geocell-reinforced bases in-filled with poorly-graded Kansas River sand (KR sand), QW, and well-graded AB-3. The influences of both single and multiple geocell reinforcements with different infill materials are compared and evaluated in terms of permanent deformation, traffic benefit ratio (TBR), and percentage elastic deformation. 4 Material and Test Equipment Geocell type and characteristics Geocell made of novel polymeric alloy (NPA) was used for the tests in this study. NPA is a nano-composite alloy of polyester/polyamide nano-fibers dispersed in polyethylene matrix and characterized by flexibility at low temperatures similar to HDPE with elastic behavior similar to engineering thermoplastic. NPA geocells have a lower thermal expansion coefficient and higher tensile stiffness and strength than HDPE geocells. The coefficient of thermal expansion (CTE) of the Neoloy element used to make the geocell, measured using ASTME831 was less than 80 ppm/0C in the measurement range from -300C to +300C. The geocell used in the experiments had the tensile strength of 19.1 MPa and the elastic modulus of 355 MPa at 2% strain. 2% strain was chosen to characterize the stress-strain of geocell because the field studies have shown that the measured strains in geosynthetics are typically within 2%. Almost identical test results on wide-width
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