Backcalculation of pavement layer properties from deflection data

A computer program named MICHBACK has been developed for the backcalculation of pavement layer properties. The program uses a modified Newton algorithm to backcalculate pavement layer moduli and thicknesses from measured surface deflections. It is shown that the newly developed algorithm to predict the roadbed soil modulus at the cost of only a single call to a mechanistic analysis program is accurate. An iterative modified Newton method to calculate the stiff layer depth from deflection data is presented and its accuracy is discussed. The ability of MICHBACK to predict any one of the layer thicknesses along with layer moduli from deflection data is presented. An extensive sensitivity analysis of the backcalculated results to the initial seed moduli is included. Some of the user-friendly features of the MICHBACK program are also presented.;The program has been extensively tested using theoretical deflection basins generated by using a multilayer linear elastic program, as well as field data obtained by using a falling weight deflectometer (FWD). The results of these tests which validate the accuracy and robustness of the program are included. The sensitivity of the results to many factors known to affect the backcalculation results are also explored. The capabilities of the program have been compared with other leading backcalculation programs and the results indicate the superiority of the MICHBACK program in many aspects. The effect of temperature on the backcalculated layer moduli has also been examined.