Probabilistic method for evaluating the permanent strain of unbound granular materials under cyclic traffic loading

Abstract In this study, a series of large-scale cyclic triaxial tests with different water contents (w), confining pressures (σ3), and dynamic deviatoric stresses (σd) is performed to investigate the accumulative permanent strain (ep) behavior of an unbound granular material (UGM) used in the construction of railway subgrade beds. Results indicate that an increase in confining pressure effectively inhibits the development rate of ep, and the ep behavior of stable specimens can be categorized into an initial rapidly increasing stage and a subsequent gradual stabilization stage, with different causes of material strain at each stage. The permanent strain accumulated from the first loading cycle, i.e., the model parameter a, demonstrates a power function relationship with the dynamic-static deviatoric stress ratio (η), and the model parameter b, which implies the increasing rate of ep, is strongly correlated with η and w. A probabilistic method based on a semi-logarithmic prediction model and probabilistic failure theory is proposed to evaluate the development range of ep of UGMs while considering the effects of the confining pressure, dynamic deviatoric stress, static failure deviatoric stress, and water content. Applications of the proposed method indicate that the developed probabilistic model can yield acceptable ep predictions of UGMs.