IN SITU SUBGRADE MATERIAL CHARACTERIZATION USING DCP AND FWD DATA

This paper gives results from Automated Dynamic Cone Penetrometer (DCP) and Falling Weight Deflectometer (FWD) testing on compacted subgrade at 12 selected pavement construction sites in Mississippi. The primary aim of this study was the development of a simple computerized procedure to determine resilient modulus of subgrade soils from DCP data files for designing pavements. The study sites covered fine- and coarse-grained roadbed soils, undisturbed sampling, and lab resilient modulus testing. Subsequently, additional FWD and DCP tests were conducted after the lime stabilization of 152.4 mm (6 in.) of subgrade soils, after the construction of 152.4 mm (6 in.) Lime Fly Ash (LFA) base, and after asphalt paving. Analysis of this FWD data shows the effects of constructed layers on in situ subgrade modulus. Modulus backcalculation using deflection data collected on the top of the subgrade was a real challenge in this study because of abnormally high deflections of sensor 1 and sometimes extremely low deflections at sensor 7. The newly developed FWDSOIL backcalculation program uses only sensors 2 through 6 deflections to determine Youngs moduli of soil layers. The DCPAN program, developed herein, automatically plots penetration data and DCP index (DCPI), assigns layer thicknesses, and generates average Youngs modulus profile at each location. This offers a simplified automatic procedure to characterize subgrade soil layers and their modulus values from DCP data for routine pavement designs.