Styvhetsanalys av vägkonstruktioner
Sammanfattning: In order to measure the stiffness properties of a soil, a method called the plate loading test is used. Based on this test a modulus called Ev2 [Pa] is obtained among others. When building a road construction there are different requirements for this Ev2-modulus for different layers in the road. According to the Swedish Transport Administration regulatory document TRVK Väg and the dimensioning category 2, the thickness of the unbounded layers in the road construction are not allowed to be less than 500 mm, which leads to that there are no defined Ev2-requirements for constructions where the thickness of unbound layers is less than this. When coarse-grained and composite soils, which are included in material type 2 and 3B, have a good bearing capacity, road structures built on these soils easily, from a bearing capacity standpoint, could have been constructed with a thickness of the unbound layers that is thinner than 500 mm. When these soils are found in the south of Sweden the ground frost would not be a problem, especially due to the low frost susceptibility of the soil. By using numerical analyses in COMSOL Multiphysics a relationship between Young's modulus E of a soil and the measured Ev2 is established. Using this result it is investigated for which values of Ev2 a subgrade consisting of coarse-grained and composite soils should have for making it acceptable to reduce the thickness of the unbound layers below 500 mm. The evaluation is based on the strain- and bearing capacity requirements defined by the Swedish Transport Administration with help of PMS Objekt and COMSOL Multiphysics and plate loading tests on the mentioned type of subgrades. Results from analyses show a linear relationship between Young's modulus E of a soil and measured Ev2-modulus. Based on this, exponential required Ev2-relationships are derived for subgrades consisting of coarse-grained and composite soils which depend on the thicknesses of the unbound layers and the traffic load. These new recommended requirements appear to be properly aligned with the existing ones.
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