Sanat K. Pokharel

Performance of Geocell-Reinforced RAP Bases over Weak Subgrade under Full-Scale Moving Wheel Loads

Recycled asphalt pavement (RAP) has been increasingly used as an energy efficient and environmentally friendly paving material and is currently the most reused and recycled material in the United States. RAP has been used in new hot mix asphalt (HMA) mixtures and in base courses for pavement construction. When RAP is used as a base course material, the presence of asphalt in RAP may cause excessive deformation under traffic loading. Geocell, three-dimensional (3D) polymeric geosynthetic cells, was proposed in this study to minimize the deformation by confining the RAP material. Full-scale accelerated pavement tests were conducted to evaluate the effect of geocell reinforcement on RAP base courses over weak subgrade. Two types of RAP were used and a total of seven geocell-reinforced and unreinforced RAP sections were tested under full-scale traffic loads. The road sections were excavated and examined after each moving wheel test. The benefits of geocell reinforcement were evaluated in rut depths for a specific number of passes of the wheel load and the angle of stress distribution from the surface to the base course-subgrade interface. The test results demonstrated that the novel polymeric alloy geocell reinforcement improved the performance of unpaved RAP sections by widening the stress distribution angle and reducing the rut depth if the base courses were equally compacted in unreinforced and reinforced sections.

Performance of Triangular Aperture Geogrid-Reinforced Base Courses over Weak Subgrade under Cyclic Loading

AbstractGeogrid (uniaxial or biaxial) is one type of geosynthetics that has been successfully used in slopes, walls, roads, and other applications. The main application of biaxial geogrid is to stabilize soft subgrade and reinforce weak base courses by providing lateral confinement. The confinement due to the interaction between aggregates and the ribs of biaxial geogrid depends on the geometry properties of the geogrid, such as rib shape and apertures size, the stiffness of the ribs, and the properties of aggregates. Research has shown that biaxial geogrid cannot provide uniform tensile resistance in all directions. To overcome this problem, a geogrid product with triangular apertures was developed and introduced into the market. Recent studies showed that the triangular aperture geogrid can provide nearly uniform tensile resistance in all directions and is more efficient in improving the performance of reinforced bases as compared with biaxial geogrid. However, the performance of triangular aperture geo...

Accelerated Pavement Testing of Geocell-Reinforced Unpaved Roads over Weak Subgrade

Full-scale trafficking tests were conducted to evaluate the effect of novel polymeric-alloy geocell reinforcement on base courses for low-volume unpaved roads over weak subgrade. Three types of in-fill materials—crushed limestone (AB-3) aggregate, quarry waste (QW), and recycled asphalt pavement (RAP)—were used for the base courses over a weak subgrade layer consisting of A-7-6 clay. Four unpaved sections that included one unreinforced control section of AB-3 aggregate 30 cm thick and three 17-cm novel polymeric-alloy geocell-reinforced sections were tested under a single-axle dual-tire wheel loading. The road sections were exhumed and examined after the moving-wheel test. The benefits of novel polymeric-alloy geocell reinforcement were evaluated in relation to rut depths for a specific number of passes of the wheel load and the angle of stress distribution from the surface to the base course–subgrade interface. The test results demonstrated that the novel polymeric-alloy geocell reinforcement improved the performance of unpaved AB-3 and RAP sections. The QW section also showed better performance in relation to stress distribution angle.

Stress Analysis on Triangular-Aperture Geogrid-Reinforced Bases over Weak Subgrade Under Cyclic Loading: An Experimental Study

Geogrids have been successfully used to improve soft subgrade and reinforce weak base courses for low-volume roads by providing lateral confinement. However, uniaxial and biaxial geogrids with rectangular or square apertures cannot provide uniform resistance in all directions. A new geogrid product with triangular apertures was developed and introduced into the market to overcome this problem. The triangular-aperture geogrid has a more stable grid structure and can provide uniform resistance in all directions compared with uniaxial and biaxial geogrids. However, the performance of triangular-aperture geogrid-reinforced bases has not been well evaluated. In this study, unreinforced and triangular-aperture geogrid-reinforced bases over a weak subgrade were constructed in a large geotechnical testing box (2 × 2.2 × 2 m) at the University of Kansas and tested under cyclic loading. During the tests, surface deformations and vertical stresses at the interface between the base and the subgrade were monitored. The test results showed that triangular-aperture geogrids reduced permanent surface deformations and vertical stresses at the interface compared with an unreinforced base. The benefit became more pronounced when a heavier-duty geogrid was used. The backcalculations from the measured vertical stresses at the interface between base and subgrade showed that the stress distribution angle and the modulus ratio of base course to subgrade decreased with an increase in the number of cycles. The rates of reduction in the stress distribution angle and the modulus ratio for the unreinforced base were faster than those for the reinforced bases. This paper focuses on the stress analysis of the test sections under cyclic loading.

Behavior of Geocell-Reinforced Granular Bases under Static and Repeated Loads

Geosynthetics have been used for base reinforcement since 1970s. Numerous research has already been carried out for planar geosynthetic reinforcement but limited research has been conducted for three-dimensional geocell reinforcement. Literature review has also demonstrated a significant gap between the applications and theories of geocell reinforcement outlining the need for more research. This study was to investigate the behavior of reinforced bases using a single geocell under static and repeated loads on a loading plate. The experimental results show that the single geocell could increase the stiffness by approximately 50% and the maximum load by 100% as compared with those of the unreinforced base. The repeated test shows that the geocell-reinforced base had the percentage of elastic deformation increase with the number of cycles of the repeated load up to 95%.

A Large Test Box Study on Geocell-Reinforced Recycled Asphalt Pavement (RAP) Bases over Weak Subgrade under Cyclic Loading

Currently, great emphasis is placed on sustainable construction and infrastructure with green technologies. As a result, the demand for sustainable and environmental friendly roads is increasing day by day. More technologies for sustainable roadway construction are needed. One way to construct environmentally sound roads is through the use of recycled asphalt pavement (RAP) materials as a base course. However, limited research has been done to quantify its structural capacity with engineering properties. It is expected that RAP base courses may have excessive deformation under traffic loading due to the existence of asphalt in RAP. It is believed that geocell confinement can reduce the permanent deformation and improve the performance of RAP bases. In this study, three-dimensional novel polymeric alloy (NPA) geocell was used to confine RAP bases. To investigate the effect of geocell confinement on the performance of road bases, unreinforced and geocell-reinforced RAP bases were constructed over weak subgrade (target California bearing ratio of 2%) in a large geotechnical test box (2 m x 2.2 m x 2 m high) and tested under cyclic loading. The test results showed that geocell confinement reduced the permanent deformation and vertical stress distribution at the interface between base and subgrade, and increased percentage of elastic deformation as compared with the unreinforced base.

Experimental Study on Triaxial Geogrid-Reinforced Bases over Weak Subgrade under Cyclic Loading

Geogrids have been successfully used to improve soft subgrade and reinforce weak base course by providing lateral confinement. However, uniaxial and biaxial geogrids cannot provide uniform resistance in all directions. A new product termed “Triaxial geogrid” was developed to overcome this limitation. The triaxial geogrid is expected to have a more stable grid structure to provide uniform resistance in all directions as compared with uniaxial and biaxial geogrids. However, the effects of the triaxial geogrids on the performance of reinforced bases have not been well evaluated. In this study, unreinforced and triaxial geogrid-reinforced bases over a weak subgrade were constructed in a large geotechnical testing box (2m x 2.2m x 2m high) at the University of Kansas and tested under cyclic loading. During the tests, the surface deformations and the vertical stresses at the interface between the base and the subgrade were monitored. The test results showed that triaxial geogrids increased percentage of resilient displacement and reduced permanent displacement and vertical stresses at the interface as compared with the unreinforced base.

Determination of Resilient Modulus of Subgrade Using Cyclic Plate Loading Tests

Resilient modulus of subgrade is often necessary for pavement design and determined by cyclic triaxial tests or correlation with other laboratory or insitu test results (such as CBR and DCP data). Cyclic plate loading tests were conducted in this study to determine the resilient modulus of a weak subgrade. The weak subgrade was made of 75% Kansas River sand and 25% kaolin and compacted at wet of optimum in a large geotechnical testing box (2m × 2.2m × 2m). This subgrade was first evaluated by DCP tests and then tested under a 30-cm diameter rigid plate at four different magnitudes of cyclic loading. During the tests, the deformations of the plate and the subgrade surface were monitored. The test results showed that the plate deformation increased with the number of cycles. An elastic solution was used based on the rebound deformation of the plate to calculate the resilient modulus of the subgrade. The calculated resilient modulus of the subgrade decreased and approached a stable value with the number of cycles under different magnitudes of cyclic loading. The calculated resilient modulus from the cyclic plate loading tests was compared with that determined based on the correlation with the CBR value of the subgrade.