A Study on FWD Deflection Bowl Parameters for Structural Evaluation of Flexible Pavement

Abstract

The application of falling weight deflectometer (FWD) is to evaluate structural condition of the pavement. The exercise of backcalculation is required to identify the modulus of elasticity of existing in service pavement. The process of backcalculation required in depth field experience for the input of range of modulus of elasticity of bituminous, granular and subgrade layer, and its required number of trial to find such matching moduli with the observed FWD deflection on the field. The study carried out at Barnala-Mansa State Highway, length 20 km at Punjab state using FWD before and after overlay; the deflections obtained at 0 on the load cell, 300, 600, 900,1200, 1500 and 1800 mm interval from the load cell. The seven deflection results are used to calculate deflection bowl parameter such as Surface Curvature Index (SCI), Middle layer Index (MLI) and Lower layer index (LLI). This SCI, MLI and LLI indices are useful to predict the structural performance of in service pavement layers and also useful to identify homogeneous section for condition assessment. The study shows that the limiting value of SCI is found 240 micron above this value the structural condition of pavement is to be considered as poor and below 100 micron it is considered as very good. The MLI values found in the range of 140 and 100 micron for old and new pavement, respectively; in both cases middle layer condition is good and it also correlates with backcalculated moduli value of middle layer. The average LLI values are found in 20 for old and 14 for new pavement; in both the cases lower layer condition is good and it also correlates with backcalculated moduli values of lower layer.