Research on feasibility of plate loading testing on highway pavement layers

Plate loading tests are used abroad in evaluation and design of flexible pavements by several organisations such as Illinois Department of Transportation (IDOT), Colorado Department of Transportation, Minnesota Road Project (MnROAD), ... etc. In Turkey, there are few organisations that use plate loading tests. California bearing ratio tests (CBR) and in recent years the falling weight deflectometer tests (FWD) are used in soil layer mechanistic evaluations. FWD tests are very expensive and can give misleading results for thin pavement layers. The plate loading test is important such that it gives the reaction coefficient value, k, of the layer.In this study, the reliability of the plate load test on highway pavements is researched by focusing on the test device dimensions and load applied during the test procedure. The ANSYS finite element modelling was utilized to determine the stress distributions through the pavement layers. It was found that the plate thickness does not have significant effects on the results based on the stress variation through the layers. The diameter of the plate indicated significant effects on the results. Plate diameters above 100 cm are suggested to obtain proper results. More importantly, the applied load has the highest impact on the test results. It is computed that the peak force on the plate should be less than 10 kN during the test. Otherwise it is possible that the plate load testing might be measuring the below sublayers characteristics.