How to Determine the Stiffness of the Pavement's Upper Layer (Base) Based on the Overall Stiffness and the Stiffness of the Lower Layer (Subgrade)

In road construction, it is important to estimate difficult-measure stiffness of the pavement’s upper layer based the easier-to-measure overall stiffness and the stiffness of the lower layer. In situations when the overall stiffness is not yet sufficient, it is also important to estimate how much more we need to add to the upper layer to reach the desired overall stiffness. In this paper, for the cases when a linear approximation is sufficient, we provide analytical formulas for the desired estimations. 1 Formulation of the Problems Need for multiple-layer pavements. Usually, the soil is not stiff enough to serve as a base for the road. Two ideas are used to reach the desired stiffness: • first, the soil is compacted, to increase it stiffness; • second, on top of the compacted soil – which now serves as a subgrade – a stiffer layer of another material (“base”) is placed (and then compacted too). How to characterize stiffness. Stiffness describes how much the pavement is displaced under the external force: the smaller the resulting displacement, the