Back-calculating structural pavement parameters

In pavement evaluation surveys, the structural condition is deduced from Falling Weight Deflection response. The recorded deflections are converted into a pavement model to assess the dynamic pavement performance.

Pavement Modelling using Surface Deflections

FWD enables pavement engineers to determine feasible maintenance and rehabilitation measures. The FWD-field survey results can be analysed within the back-calculation suite of PAVERS ®. The structural pavement parameters is determined by comparing measured deflections with calculated deflections using the mathematical models. The structural pavement parameters e.g. the concrete slab and its foundation characteristics and the elastic moduli of distinct pavement layers in flexible pavements are derived from an iterative computer based technique in which a deflection bowl is calculated from assumed combinations of input values. The structural parameters are adjusted until the computed deflections and SCI under a given load agree closely with the corresponding measured deflections and surface curvature index (SCI). If the calculated deflection at each point matches the measured values to within a fit of say 2%, no further refinement is required. The structural parameters obtained this way are considered representative for the pavement structure under consideration.

The program allows for back-calculating flexible and rigid pavement. The tool has an automatic back-calculation routine for flexible pavements. Deflection basins and construction data can directly be read from Excel files. For rigid pavement, the user can either back-calculate deflections at the slab interior or at the slab’s joint. For the latter, the deflection transfer across the joint is required as an additional input value. The friction between two layers and the layer thickness can either be fixed or set variable in the back-calculation routine.