Verification of stiffness modulus of road bases and sub-bases

Resumen

The results of a study on the development and applicability of the Light Weight
Deflectometer (LWD) and Falling Weight Deflectometer (FWD) for the verification of the
quality of bearing capacity of road bases and sub-bases are presented. Relationships have
been developed between the bearing capacity and stiffness moduli of base courses and subbases
and the stage of completion of the road. In any pavement design assumptions are made
for the stiffness moduli of all constituent layers. The stiffness of a sand sub-base for example
may be set to a value of 100 MPa. After construction of this sand sub-base an LWD test may
provide data on the stiffness of the layer. This stiffness will be lower than used in the
pavement design. Differences in load spreading and confinement in each construction stage
may be the predominant causes. A model has been developed to assess how the lower seated
layers stiffen with each extra layer, both due to overburden stress and changes of load
spreading. The model is easy-to-use and does not require complicated stress dependency
characteristics although these characteristics have been used in the development of the tool.
The model can be used to assess the current stiffness modulus but also to predict whether the
targeted design stiffness will be achieved. The paper addresses the development of the tool,
the use of it in quality control and the predictive accuracy.