Selection of suitable backcalculation technique and prediction of laboratory resilient modulus from NDT devices

This study aims to analyse the backcalculated cohesive subgrade moduli using various backcalculation approaches. A series of in situ and laboratory investigations have been carried out on 190 test locations from 30 pavement sections of cohesive soils using Falling Weight Deflectometer (FWD), Light Weight Deflectometer (LWD), and Repeated Load Triaxial to determine backcalculated resilient moduli (MR_back), composite resilient moduli (MR_comp), and laboratory resilient modulus (MR_lab). The comparative analysis was performed for MR_back by LWD (MR_back_LWD), MR_comp by LWD on subgrade (MR_comp_LWD), and MR_back by FWD (MR_back_FWD) with MR_lab values to assess the level of agreement. MR_back_FWD and MR_back_LWD values of different soils by using Artificial Neural Network and Support Vector Machine techniques have shown the mean percentage variation (1.16–59.63%), correlation in terms of R2 value (0.628–0.824), and RMSE value (0.51–20.49%) with MR_lab values. In contrast, MR_comp_LWD values have shown good agreement with MR_lab values among MR_back_LWD and MR_comp_LWD. This study also suggested adjustment factors (0.308–0.974) for predicting MR_lab values from MR_back_FWD and MR_back_LWD for cohesive soils. Thus, this study recommends an appropriate backcalculation technique and suggests adjustment factors to the cohesive type of soils for realistic prediction of resilient characteristics of subgrade.