ABSTRACT
The plate load test is commonly used to determine the bearing capacity of unbound granular materials. It is widely used in road construction, and the test is mandatory as final documentation of compaction quality of unbound layers of pavements in Norway. The test is sensitive to field conditions and test execution, and several Norwegian contractors struggle to meet requirements for the test results despite repeated compaction efforts. This paper aims to assess the effects of in-situ road conditions, the superstructure materials and the test procedure and calculation method on the results of plate load tests. A case study and a field test were conducted. The case study compared four different road construction sites in Norway based on results from semi-structured interviews, collected results of plate load tests and field observations. Additional interviews and plate load test results from other road construction sites were also considered, although not for direct comparison in the case study. The field test applied two test procedures (Norwegian and Swedish) and two plate sizes (300 and 600 mm) on three superstructure layers (frost protection, subbase, and interlocking layers). The results of all tests were calculated using three calculation methods; the Swedish method, the Norwegian method, and a modified Norwegian method. The interview results indicate that crushed asphalt and/or insulation materials in the superstructure, moisture content and time from compaction to testing are the most influential factors on the plate load test results, although this should be verified with further testing. The field test results suggest that the interlocking material is important to fulfil the requirements for the E2/E1 value. The use of different test procedures and calculation methods showed significantly different results in some but not all cases and should therefore be investigated further. Other comparisons were largely inconclusive, likely due to limited number of tests.
