None of the existing backcalculation procedures is guaranteed to give a reasonable, effective elastic layer modulus for every deflection basin measured. The differences of results among various backcalculation programs are magnified by the differences of distinct analysts using the same program but applying different input parameters. A more experienced analyst often may obtain better results. Some of the difficulties, such as the deviation of pavement material properties from the linear elastic, isotropic, and homogeneous assumptions, the uncertainty of input parameters (for example, the deflection measurement), and the limitation of basin matching techniques, may only be dealt with by informed engineering judgement. A knowledge-based expert system approach as described in this paper may be used to generate more consistent and better estimations of in situ pavement material properties by combining numerical computations with a pavement expert's knowledge and judgement. A knowledge base which serves as an intelligent pre- and postprocessor to the backcalculation program is developed. The knowledge base may be revised easily as better understanding emerges.

The proceedings of June 1993 international symposium held in Atlanta, Georgia, called specifically to develop and standardized evaluation procedures for non-destructive methods of testing pavements. The 29 papers discuss analytical models and techniques, measurement and calculation techniques in the field and laboratory, problems and errors associated with backcalculation methods and design parameters, and testing for other pavement uses. Also includes a history of the quest for a standard and the status of that effort. Reproduced from typescripts. Annotation copyright by Book News, Inc., Portland, OR

As with the previous two symposia, the 32 papers from the June/July, 1999, Seattle symposium present advances in the nondestructive testing of pavements using conventional falling weight deflectometer techniques and other promising techniques such as ground penetrating radar, rolling weight deflecto