Utvärdering av bärighetskrav i totalentreprenader

Sammanfattning: To achieve maximum benefit with both resources and money, the Swedish Transport Administration want to set requirements regarding the bearing capacity in design and construct contracts to ensure a long lifetime of roads. A falling weight deflectometer test is to be carried out for the final inspection of the road and the results will tell the Swedish Transport Administration whether the contractor has met the demands regarding bearing capacity or not. The objective of setting these requirements is to make the contractor more thorough with the compaction work and make them identify and address weaker sections in the subgrade early in the construction process. This master thesis is about different measurements of bearing capacity that are described by the Swedish Transport Administration. A comparative study between these measurements is carried out, partly based on calculations from falling weight deflection data, and partly based on semi structured interviews with representatives within the field of road engineering. Important aspects regarding FWD, such as temperature, moisture content and time of loading has been discussed during the interviews, both when it comes to performing the tests and to analyze the data. Measurements of the stress tension at the bottom of the asphalt layer can be corrected for varying temperatures. However, research show that for road constructions with a thinner asphalt layer <75 mm such as cycle paths, different kinds of measurements should be used. The results are to be assessed with care since the Swedish Transport Administration’s computing models are not designed for thin asphalt layers. This thesis show that temperature correction for thin asphalt layers is possible to perform, but the accuracy of results will vary greatly depending on what correction methods that are used. More research should be carried out to be able to correct measured deflections or calculated stiffness modulus due to varying moisture content in the unbound granular layers. The conclusion from this thesis is that different measurements of bearing capacity should be used (surface modulus for cycle paths and bearing capacity class for normal Swedish roads). Depending on the type of road that is constructed (normal road or cycle path) the requirements are to be presented as low percentile values instead of mean values. The reason for this is to avoid that weaker sections are overlooked at the final inspection.