Volume 23, Issue 3 (May 1995)
Characterization of Base/Subbase Materials under Repetitive Loading
Testing of granular materials for evaluation of Resilient Modulus (MR) suffers from the lack of a standardized test method. Although AASHTO over the past six years (1986 to 1992) has proposed three different testing procedures (T274-86, T292-91I, and T294-92I), some state transportation departments have adopted their own MR testing procedures. In this study, the factors affecting the measurement of MR such as the testing method used and stress applied and its sequence are investigated. In addition, the updated methodologies proposed by various agencies for MR of granular materials and the MR values obtained are reviewed and evaluated. It is found that the applied stress sequence has some effects on MR of granular materials. For the two aggregate types investigated in this study, with the same location of LVDT and dynamic waveform, the T294-92I testing procedure yields higher MR than that obtained by using the T292-91I testing procedure. The stress sequence in T294-92I infers a stiffening and strengthening effect on the specimen structure as the stress level increases from low to high. The variation of MR values due to testing procedure is found to be higher than those due to the aggregate source. The MR values obtained in this study are found to be lower than those reported in the literature. Furthermore, with the updated testing procedure for MR, the correlation between the structural layer coefficients and MR of granular base and subbase proposed by the AASHTO needs to be modified accordingly.