Falling Weight Deflectometre And Plate Load Test: Direct And Indirect Comparative Testing

Plate load test is a widely used method in Latvia both in quality control and in road design process. This test is performed according to the standard DIN 18134. Such test usually takes at least 30 minutes and requires certain load weight. Considering the relatively long time needed for this test, alternatives were sought and a potential alternative was defined to perform testing with Falling Weight Deflectometre (FWD). In order to check this assumption both direct and indirect testing was performed and correlation between the results of both tests was defined. In the first case the test was performed in the same location with both pieces of equipment on a surface of unbound pavement. In the second case the test with Falling Weight Deflectometre was performed on the surface of bituminous pavement but plate load test was performed in the same location on the surface of base course with prior demolition of bituminous layers. In order to compare the results of indirect comparative testing, the backcalculation for the data acquired with Falling Weight Deflectometre was performed according to German calculation method. Results acquired with direct testing showed that the testing with Falling Weight Deflectometre and plate load test are interchangeable if no characterization of the layer compaction is required. The German method of backcalculation (FGSV, 2014) is very simple. Despite positive references from other specialists this method in comparative testing did not show sufficiently good correlation with the results acquired in plate load test.