ABSTRACT
Deflection data from a falling weight deflectometer (FWD), a nondestructive impact test, are used to backcalculate subgrade layer modulus values. It has been proved to be a very effective method of testing if good estimates of layer thickness data are used for backcalculation. Unfortunately, most of the available backcalculation programs are developed to analyze FWD deflection data collected on existing or constructed pavements. The data from a dynamic cone penetrometer (DCP), a destructive impact test, can be related to the subgrade soil material stiffness. These methods are faster and cheaper compared to the laboratory resilient modulus testing of soils. This paper introduces the newly developed FWDSOIL program (for subgrade and base sections) and the UMPED programs (for asphalt sections). These programs are used to backcalculate the modulus values of different pavement layers and subgrade. A new program DCPAN, developed for automatic reading and interpreting Automated DCP road test data files, is also described. These programs were used to analyze the test data collected on a recent research study that involved Automated DCP and FWD side-by-side testing on compacted subgrade at 12 selected pavement construction sites in Mississippi. The modulus results from the DCPAN and FWD tests agree reasonably with the laboratory resilient modulus values for the bottom subgrade layer, which is important for pavement thickness design. Effects of seasonal variability are investigated using the DCP and FWD tests conducted over summer, winter, spring, and next summer seasons. Both stabilized base and top lime-treated subgrade layers gained significantly in their Young's modulus values.
