NEW SCENARIO FOR BACKCALCULATION OF LAYER MODULI OF FLEXIBLE PAVEMENTS

Abstract

A new backcalculation scenario that uses falling weight deflectometer (FWD) deflection bowl data to directly backcalculate subgrade modulus and overall pavement modulus and predict effective structural number of the pavement is presented. The procedure allows for decomposing measured maximum deflection into two components: subgrade deflection and pavement deflection. Execution of the scenario accounts for conditions when thickness data are not available, not reliable, or not representative. The scenario depends on a concept that is not related to selection of seed values. The concept is that there is a unique location on the surface of the pavement at a radial distance r sub x from the loading center that deflects with a value D sub x exactly equal to the deflection of the point on the top of subgrade underneath the loading center. The scenario was field tested using FWD deflection measurements representing newly constructed roads, roads with considerable deterioration, top of compacted subgrade, top of subbase, top of base, and top of wearing surface. General observations on field applications and a field testing example are introduced.