5. Conditions of use for subgrade materials

According to the definition proposed by the GTR, a subgrade is a structure that adapts the random and dispersed characteristics of the backfill or excavated material to the permanent characteristics required in the pavement design.

Calculation and selection of the pavement structure are based on an economic study of the earthworks, subgrade and pavement package, carried out to optimize the project. This study must be validated in the field, using geotechnical surveys and test beds.

The subgrade is a support layer for the pavement. It is important to stress that its design is inseparable from the characteristics of the layer constituted by the upper part of the earthworks (PST).