Evaluation of Granular Fill Layer Underlain by Soft Clay Soil Using Large Scale Cyclic Plate Loading Tests

In general, granular fill materials are widely used to construct new pavement and rehabilitate old pavement. For pavement design, it is essential to know the basic characteristics, such as the permanent deformation behavior of these materials. Considering this phenomenon, this study aims to explain the performance of granular fill layers in pavement systems using cyclic plate load tests. For this purpose, a large-scale cyclic plate load test facility, also known as pavement model testing (PMT), was developed to investigate the permanent deformation characteristics of the pavement structure. To conduct experiments, a standard pavement structure was built with granular fill layers on top of a soft clay subgrade and a geotextile between the subgrade and the base layer. The PMT was used to apply a 40 kN cyclic load through a steel plate with a 305 mm diameter for up to 10,000 cycles after the pavement structure was built. A total of four tests were carried out to evaluate the effects of the granular fill layer's thickness on the pavement's permanent deformation. Furthermore, an analytical solution was developed for the fill layer thickness using the test results. Additionally, the outcomes of some previous studies in the literature were compared to the ones that were obtained. The results of this study indicate that the permanent deformations of the pavement structure and the subgrade increased with the number of load cycles. The permanent deformations began to limit at 3000 cycles when the fill layer thickness was 20 cm, but it was observed that deformations did not limit at 3000 cycles when the fill layer thickness increased to 45 cm. Also, the permanent deformations decreased by two times when the granular fill layer thickness doubled appropriately.