Abstract
The constitutive model is the crucial part for the finite element analyses. To study the elasto-plastic properties of unbound granular materials (UGMs) under repeated vehicular loads, an elasto-plastic constitutive model called revised spatially mobilized plane (SMP) was proposed and validated. In this study, the revised SMP model was used for the plastic strain analyses of a typical three-layer pavement structure. To make comparisons, the Mohr-Coulomb and Druck-Prager models were employed for the numerical computation. The results show that plastic tensile and compressive strains in the horizontal and vertical directions appear on the top surface of UGM using the revised SMP model, but no plastic strains are produced by the Mohr-Coulomb and Druck-Prager models. The distribution of plastic strains in the revised SMP model had a good relationship with the actual loading areas under the vehicular loading, which related to the rutting. With the Mohr-Coulomb and Druck-Prage models, a great plastic strain was produced during the first several loading cycles and hardly increased in the following loading cycles, while the plastic strain in the revised SMP model presented an obvious increasing tendency with increased loading cycles. The predicted permanent deformations of the revised SMP, Mohr-Coulomb and Druck-Prage models were 0.557 mm, 0.78 mm and 0.155 mm, respectively. Our work reveals that the Mohr-Coulomb model may over-predict and Druck-Prage model may under-predict the rutting of pavement in early loading stage and the results proved that the revised SMP model had advantages in the description of the plastic strain of UMG under repeated loads.
Highlights
Unbound granular materials (UGMs), which are commonly used as the base or subbase courses in flexible pavements, have excellent adaptability for different conditions.UGMs have some disadvantages affecting their usage in pavement
Druck-Prage model may under-predict the rutting of pavement in early loading stage and the results proved that the revised spatially mobilized plane (SMP) model had advantages in the description of the plastic strain of UMG
The nominal tensile strain occurred under the loading area, resulting in the lateral movement of particles, and a nominal compressive strain appears on both sides of the loading area
Summary
Unbound granular materials (UGMs), which are commonly used as the base or subbase courses in flexible pavements, have excellent adaptability for different conditions. Aiming at studying the stress-dependency of UGMs, non-linear and anisotropic models were frequently used to describe the mechanical properties of UGM in the laboratory and field [6,12,13,14,15] This kind of model was mostly used for the computation without considering the characteristics of plasticity. Compared with the nonlinear anisotropic elastic model, the NAEP model gave similar fatigue life results but predicted greater rutting in the pavement [6] This model took full account of the characteristics of UGMs, avoiding the complicated hardening law. Based on shakedown theory and the Drucker-Prager criterion, Chazallon et al established an elasto-plastic model of UGMs using a simplified model which employed the linear kinematic hardening assumption and a non-associated flow rule [3,4]. Considering the relationship among the SMP, Mohr-Coulomb and Druck-Prager criteria, these three models were used in this work for the computation of pavement analyses
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