Experimental study on the resilient behavior of unbound granular materials and the evaluation of prediction model

The resilient modulus ( M r ) serves as a key indicator for evaluating the stiffness of road subgrade and pavement base/subbase layers under long-term traffic loading. Although there have been many laboratory studies on the resilient behavior of road unbound granular materials (UGMs), and many models to predict M r have been proposed; however, the relative roles of various factors on M r and its prediction model are not clearly clarified. This study conducted a series of cyclic tests on UGMs based on a large-scale triaxial apparatus, in which various factors including the fines content, moisture content and oversized soil particle, confining pressure and initial deviatoric stress, amplitude, frequency, and waveform of cyclic stress were involved. Test results show that the effects of fines content and oversized soil particle on the resilient modulus are limited. The initial stresses are the primary factors influencing the resilient behavior, and the impact of initial deviatoric stress on M r is much smaller compared to confining pressure. Both the amplitude and frequency of cyclic stress have significant effects on M r , while the influence of loading waveform is relatively small. The prediction model of M r recommended by JTG D50-2017 is employed to fit the test results, and it is found that the loading frequency is the predominant factor influencing the regression coefficients, the initial deviatoric stress, and loading waveform are moderate factors, while the fines content and oversized soil particle are minor factors. A model involving the factor of loading frequency is proposed based on the model recommended by JTG D50-2017, and its accuracy and application upon various factors are evaluated. Based on the test results, some advice is given for the application of UGMs on road subgrade and pavement base/subbase.