Monitoring Stiffness of Gravel Surfaced Roads during Spring Thaw Using a Portable Falling Weight Deflectometer

Modulus (stiffness) is one of the primary inputs to mechanistic pavement design procedures and provides insight into long term pavement performance. Despite the importance of modulus, some aspects of pavement construction and management are still based on measurement of parameters that are not directly connected with long-term performance or on empirical based judgments. The goal of this research was to evaluate the effectiveness of the portable falling weight deflectometer (PFWD) in evaluating the support capacity of pavements during spring thaw. The performances of ten low volume roads, three of which were gravel surfaced, were evaluated through spring thaw and recovery. Instrumentation was used to measure frost penetration in the test sections on days when measurements were made. Comparisons were made to the traditional falling weight deflectometer (FWD). It was shown that the PFWD was able to follow seasonal stiffness variations and compared well with FWD derived moduli on gravel surfaces. Recommendations were made for using a PFWD to determine when to place and remove seasonal load restrictions.