More and more highway agencies are obtaining and using highway pavement deflection measuring equipment to infer the elastic modulus of paving materials for design purposes. Layered elastic theory is used in the analysis to arrive at the moduli for individual pavement layers. It is possible under certain conditions to arrive at erroneous values of the elastic moduli, particularly when a rigid layer exists below the subgrade unbeknownst to the engineer. A theoretical study was performed, for flexible pavements, to determine the sensitivity of backcalculated moduli to the existence of this rigid layer. It was found that a rigid layer will adversely affect the accuracy ofthe backcalculated pavement moduli if the actual depth of the layeris equal to or less than half its assumed depth with respect to thesurface of the pavement. These types of errors will result in unconservative pavement evaluations and designs for rehabilitation and reconstruction--leading to early pavement failure. This paper appears in transportation research record no. 1227, Rigid and flexible pavement design and analysis: unbound granular materials, tire pressures, backcalculation, and design methods.
Abstract