STRUCTURAL ANALYSIS ASPHALT PAVEMENT BY FWD AND BACKCALCULATION OF ELASTIC LAYERED MODEL . THIRD INTERNATIONAL CONFERENCE ON BEARING CAPACITY OF ROADS AND AIRFIELDS. PROCEEDINGS, NORWEGIAN INSTITUTE OF TECHNOLOGY, TRONDHEIM, NORWAY, JULY 3-5 1990. VOLUMES 1-2

This article describes a method of asphalt pavement structural analysis using falling weight deflectometer (FWD) measurements and the backcalculation of an elastic layered model. A non destructive testing method using a two mass type falling weight deflectometer mounted on a survey vehicle was used to obtain the deflection data. A backcalculation method was developed and a good relationship between layer modulus and equivalent layer coefficient was formulated. Elastic multi layer theory was adopted as a model of pavement structure. The backcalculation method minimises the errors between the measured FWD deflections and the calculated deflections and is based on the concept of non linear least square method. This method finds the set of layer moduli which corresponds best to the measured FWD deflections for various traffic classifications. In applying this system to in service pavement sections, the influence of errors in deflection measurement, layer thickness, and Poisson's ratio upon the estimated value must be taken into account. The number of FWD measurements which will provide an acceptable confidence level and which will yield a set of estimates within permissable ranges is examined. The results show that this method can effectively evaluate existing pavement condition and provide a reasonable rehabilitation design method. (TRRL)