The design methodology of a flexible pavement structures is extremely laborious and complex requiring several work steps. Thus initially are required conducting field studies on the composition
and volume of traffic, geotechnical characteristics of subgrade soil, hydrological regime of pavement system. Then follow the itself design of the pavement structure which involves the following steps: establishing the calculation traffic, determining the bearing capacity
of the road bed, the choice of an embodiment of the pavement structure, pavement structure analysis at the standard axle loading, establishing the pavement structure behaviour under the traffic. In general, in the pavement design practice is considered that the choice of a pavement structure embodiment with thicknesses as great for pavement layers and constituent materials as best ensures a good behaviour of in service pavement structure. Unfortunately is overlook the variation of the subgrade soil bearing capacity during a year due to variations n environmental conditions (humidity, temperature, freeze-thaw) specific for the road site. This paper aims to highlight the magnitude of the subgrade bearing capacity influence on the flexible pavement structures behaviour. In the study it will be shown that the stress and strain state in the pavement structure is a very sensitive indicator of the importance of road bed soil condition and quality, and as such, it is very important to take this aspect into account in
order to have not surprises during the pavement exploatation.

flexible pavement structures, subgrade soil, bearing capacity