DETERMINATION OF THE STIFFNESS MODULUS AND DENSITY OF A PAVEMENT FOUNDATION USING FALLING WEIGHT DEFLECTOMETER DURING PAVEMENT CONSTRUCTION

The in-situ stiffness modulus and the density of the subgrade play an important part in the performance of the pavement structure. The subgrade stiffness modulus is seldom determined during pavement construction. The need for an accurate and reliable subgrade characterisation is obvious to ensure adequate quality control on compaction has been realized during the construction of the subgrade layer. This paper presents a research study where the falling weight deflectometer was used to backcalculate the in-situ subgrade modulus after compaction to confirm whether the design assumptions adopted in the mechanistic-based pavement design have been achieved. The falling weight deflectometer was also used to record the subgrade deflections which can be used to indicate the subgrade uniformity and may also serve as a construction acceptance criterion for the pavement subgrade during construction. In this manner, the non-compliance sections of the subgrade layer can be detected by the deflection test and thus the subgrade construction quality and uniformity can be ensured. In the research study, a mathematical relationship has been developed between the backcalculated stiffness modulus of subgrade and the FWD deflection sensor number 1, df1. The study also indicated that the deflection parameter, df1, is significantly influenced by the densification of the pavement foundation and a unique relationship can also be established between the density of the engineered subgrade layer and the deflection parameter. A comparison was made between the FWD derived stiffness modulus and the results obtained from the Dynamic Cone Penetrometer(DCP) and the comparison indicated that consistent results were derived from both field testing devices. (a) For the covering entry of this conference, please see ITRD abstract no. E204151.