OVERLAY DESIGN BASED ON FALLING WEIGHT DEFLECTOMETER MEASUREMENTS

The technique used for measuring deflections in an asphalt pavement by means of a falling weight deflectometer is described in some detail. Two models of the deflectometer that have different force ranges have been developed at Koninklijke/Shell-Laboratorium, Amsterdam. The deflectometer is used for the routine evaluation of pavements. The data it produces are of sufficient quantity and quality to serve as input for an analytical method of overlay design. The validity of the data and the interpretation method has been verified by wave-propagation measurements. The basic principles of the new Shell design method are outlined, with specific reference to the determination of overlay thicknesses. It is shown that the required thickness of an overlay depends on one of two criteria, subgrade strain and asphalt-fatigue strain, and that all designs must be checked to determine which of the two criteria is the limiting one. To illustrate this, several examples are given. Some possible refinements to the basic overlay design procedure are discussed, such as the incorporation of various mix characteristics and the procedure for use if the type of mix to be used for the overlay differs significantly from that of the existing pavement. /Author/