BOUSDEF: A BACKCALCULATION PROGRAM FOR DETERMINING MODULI OF A PAVEMENT STRUCTURE

Highway and transportation agencies have an increasing responsibility for the maintenance, rehabilitation, and management of highways, particularly with regard to asphaltic concrete pavements. Efficient and economical methods are required for determining the structural properties of existing flexible pavements. Nondestructive testing (NDT) of pavements is one of the most useful and cost-effective methods for evaluating the structural adequacy of pavements. With the wide use of NDT, in particular the deflection test, a large amount of test data can be obtained. One common use of deflection data is to determine the pavement layer moduli through backcalculation. The microcomputer program BOUSDEF for backcalculating the moduli of a pavement structure using deflection basin data is presented. The solution techniques for use in developing the program are described, including the use of the method of equivalent thicknesses, Boussinesq theory, consideration of nonlinearity of pavement materials, and consideration of overburden pressure on stress calculation. Evaluation of the program was performed by two approaches: (a) comparing the backcalculated moduli with theoretical moduli, and (b) comparing the backcalculated moduli with results from other developed backcalculation programs. The evaluation shows that the moduli backcalculated using the BOUSDEF program compare well with the theoretical moduli and also are compatible with those from other developed programs. The BOUSDEF program runs fast compared with other backcalculation programs; therefore, the program can be effectively used as a tool to make initial evaluations of deflection testing data for determining pavement layer moduli.