Permanent Deformation and Its Unified Model of Coal Gangue Subgrade Filler under Traffic Cyclic Loading

Abstract

Using coal gangue as subgrade filler can not only solve the environmental problems of coal mine waste accumulation but also decrease the subgrade cost, which has important theoretical and practical significance. A series of cyclic triaxial tests was carried out using the large-scale dynamic and static triaxial apparatus (LSDSTA) to investigate the permanent deformation (ε) of coal gangue subgrade filler (CGSF) under cyclic loading. Experimental grading was designed by using the fractal model grading equation (FMGE), and then well-grading limits of CGSF were captured. The relationship curve between ε and the numbers of cyclic loading (N) can be divided into three stages, i.e., the rapid growth phase, the deceleration growth phase, and the approaching stability phase. N = 1000 can be used as the criterion for reaching the stable stage of CGSF. The effect of confining pressure (σ3′) on ε is related to the level of σ3′. The effect of σ3′ on ε is significant when σ3′ is smaller, whereas the influence of σ3′ on ε is smaller when σ3′ is larger. Furthermore, the influence of grading (Df) on ε of coal gangue samples is significant. With the increase of Df, ε first increases and then decreases, reflecting that there is an obvious optimal grading for coal gangue samples under cyclic loading. Moreover, the effect of compaction degree (Dc) on ε of CGSF depends on the level of Dc. ε is hardly affected when Dc is smaller, whereas increasing Dc has a significant effect on restraining ε when Dc is bigger. In addition, according to the analysis of the permanent deformation curve for CGSF, the unified calculation model of permanent deformation for CGSF under cyclic loading is established. Compared with the existing permanent deformation models, the proposed model in this paper can better describe the permanent deformation of CGSF under cyclic loading. Finally, the model parameters are analyzed, and the model is verified.