Comparative Analysis of Using Laboratory Testing and Nondestructive Testing to Obtain Subgrade Resilient Moduli

Pavement subgrade characterization in terms of resilient modulus (M_R) is essential for pavement design. This paper presented a new methodology to monitor and evaluate seasonal variation of subgrade resilient modulus. First, a kind of typical cohesive subgrade soil was tested to determine the relationship between tension (Ts) and saturation degree (Sr) utilizing soil tensiometer in laboratory, as well as the relationship between resilient modulus and saturation degree based on repeated triaxial test. The majority of the analyses had R2 values above 0.98, which indicated that a good correlation exists between tension, saturation degree and resilient modulus. Thus it is allowed to predict the resilient modulus of cohesive soil from the tension. In addition, a road section was instrumented, coupled with Falling Weight Deflectometer (FWD) deflection tests monthly over a period of a year. Further, AASHTO equation method and MODULUS program were both used to back-calculate the subgrade modulus based on the FWD deflection data. Finally, a corrective coefficient was suggested for pavement design when using the MODULUS program to back-calculate the sub grade modulus. A comparative analysis was conducted throughout the above process.