Backbone curves of subgrade silty filler under intermittent train-induced loading

Abstract

The loading intermittence duo to the time interval between adjacent passing trains is conducive to improving the dynamic stability of railway subgrade, but this intermittence effect is always ignored in existing experimental studies on the dynamic characteristics of subgrade fillers in which a continuous cyclic loading method was adopted to simulate the long-term train-induced loading on subgrade. This paper aims to study the backbone curves of subgrade silty filler under intermittent train-induced loading, considering the time interval between adjacent passing trains. By conducting a series of intermittent cyclic triaxial tests on silty filler, the backbone curves of each loading stage were constructed, and the effects of loading intermittence on the backbone curves were elaborated. The experiment results indicate that the loading intermittence enhances the resistance of subgrade silty filler to the dynamic loading and is conducive to the upward deviation of the backbone curves. The loading intermittence could effectively increase the ultimate value of dynamic stress amplitude that the silty filler could bear under cyclic loading, but has little effect on the maximum/initial resilient modulus. The backbone curves increase approximately linear under the states of plastic shakedown and plastic creep, but show significant nonlinearity after including the incremental collapse samples. Hyperbolic models for backbone curves such as H-D model and its improvement model could be adopted to characterize the backbone curves of silty filler under intermittent loading, and the normalization of H-D model was also discussed to integrate the influencing factors (i.e., moisture content and confining pressure) of the backbone curves.