Evaluation of nondestructive testing data using AASHTO and WESDEF backcalculation approaches

This paper presents an evaluation of the falling weight deflectometer "FWD" testing data using the AASHTO and WESDEF backcalculation procedures. The backcalculated layer moduli and effective structural number "SN_eff" of an existing flexible pavement were determined from both procedures. The subgrade modulus of resilient "MR" obtained from WESDEF was found to be about 0.7 to 0.9 the value obtained from AASHTO with factor "C" of 1.0. Modulus values obtained based on CBR tests indicated that AASHTO gives more realistic MR values when the factor "C" is set to 0.33, as recommended by AASHTO for this factor. The analysis also suggests that a similar factor, about 0.43, should be considered with WESDEF to produce M_R values comparable with CBR related modulus values. Using WESDEF results without adjustment has led to higher estimate of the SN_eff value compared with AASHTO. The difference in SN _eff values was examined at various reliability levels and found not to be significant at the 5% significance level when a reliability level up to 90% is considered. Beyond this level of reliability, the WESDEF produced SN _eff difference that is significantly high, reaching up to 0.44 and 0.66 for reliability levels of 95 and 99%, respectively. Based upon this study, AASHTO may be recommended for design of heavy trafficked facilities whereas WESDEF would be suitable for less trafficked projects but in the latter case AASHTO would still be usable.