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 ($\epsilon$) 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 $\epsilon$ 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 (${\sigma }_3^{\prime }$) on $\epsilon$ is related to the level of ${\sigma }_3^{\prime }$. The effect of ${\sigma }_3^{\prime }$ on $\epsilon$ is significant when ${\sigma }_3^{\prime }$ is smaller, whereas the influence of ${\sigma }_3^{\prime }$ on $\epsilon$ is smaller when ${\sigma }_3^{\prime }$ is larger. Furthermore, the influence of grading ($D_f$) on $\epsilon$ of coal gangue samples is significant. With the increase of $D_f$, $\epsilon$ 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 ($D_c$) on $\epsilon$ of CGSF depends on the level of $D_c$. $\epsilon$ is hardly affected when $D_c$ is smaller, whereas increasing $D_c$ has a significant effect on restraining $\epsilon$ when $D_c$ 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.

Coal gangue, as a subgrade filler, is of great significance for the sustainable development of the economy, society, and environment. Particle crushing tests were conducted on coal gangue coarse-grained subgrade filler (CGSF) under uniaxial compression conditions, and the relationships between load and displacement, crushing strength, failure pattern, and gradation after crushing were analyzed. A new visual analysis method for the crushing patterns of particles was provided through image analysis, and a new gradation equation based on the traditional fractal model was proposed to describe the crushed particles. The results indicate that as the particles are gradually compressed the sharp corners of particles are gradually crushed and fall off, causing the relationship curve between load and displacement to fluctuate and grow, and particle splitting failure leads to the approximately linear growth curve. Moreover, the distribution of particle crushing strength for coal gangue is between 3.02 and 11.11 MPa, and the crushing probability and the applied load well satisfy the Weibull distribution function. Furthermore, as the particle size decreases, the shapes of crushed coal gangue particles are block, flaky, acicular, and powder, and the particles with a size greater than 5 mm are mainly flaky. In addition, comparative analysis shows that the new gradation equation can better describe the gradation of coal gangue fragments after crushing.

The accumulation and discharge amount of coal gangue are substantial, occupying significant land resources over time. Utilizing coal gangue as subgrade filler can generate notable economic and social benefits. Coal gangue coarse-grained soil (CGSF) was used to conduct a series of large-scale vibration compaction tests and large-scale triaxial tests. The results indicate that the maximum dry density of CGSF initially increases and then decreases with the increase in fractal dimension. The stress–strain curves of the samples exhibit a distinct nonlinear growth pattern. Analysis of the compaction effect suggests that the compaction degree of CGSF should not be lower than 93%. As the confining pressure increases, the extent of failure strength improvement due to increased compaction decreases. Additionally, the failure strength of samples initially increases and then decreases with the increase in coarse particle content. A modified quadratic polynomial fractal model gradation equation was proposed to describe the gradation of samples after particle breakage. Based on this, a new quantitative index for particle breakage was established. Analysis of particle breakage in samples revealed that higher confining pressure and greater coarse particle content lead to increased particle breakage. The breakage exhibited a significant size effect, and the impact of particle gradation on sample breakage was greater than that of confining pressure. The stress–strain relationship of CGSF was analyzed by using a logarithmic constitutive model, and the correlation between model parameters and the newly derived particle breakage index was generated. A constitutive model incorporating particle breakage for CGSF was established, and its accuracy was validated.

Soil–rock mixture (S–RM) is a heterogeneous granular material commonly used in engineering applications, but achieving uniform particle mixing is challenging. This study investigated the effect of mixing homogeneity on the compaction of S–RM using the discrete element method (DEM). Specimens with varying degrees of mixing were modeled under realistic vibration loading. The results showed that a higher degree of mixing resulted in a smaller void ratio after compaction. The analysis of particle motion and energy dissipation revealed that not all particle motion during vibration compaction was aligned with the direction of the particle system. However, rotation was more prevalent and contributed to densification. Dashpot energy dissipation did not solely promote changes in the void ratio, while slip energy dissipation did lead to changes in the void ratio, but not entirely towards compaction. Rolling slip energy dissipation primarily occurred during the stage of void ratio changes and significantly promoted compaction. The change in strain energy aligned with the trend of the void ratio but did not directly contribute to its promotion.

Prolonged drought can induce shrinkage cracking in near-surface clay foundations, leaving persistent defects that may affect the uplift safety of underground structures before subsequent rainfall events. This study investigates how burial depth regulates the influence of two pre-existing surface cracks on the uplift bearing capacity and failure mechanism of a horizontal strip anchor plate in red clay. A two-dimensional plane-strain model was established in Optum G2 and validated against laboratory pull-out tests under crack-free conditions. Two burial-depth ratios, H/B = 3 and 8, were examined, and 360 cases were generated by varying normalized crack depth (h/B = 0.25–3), spacing (s/B = 0.25–3), and horizontal offset (d/B = 0–6). Under shallow burial, cracks readily intersect the potential sliding zone and the maximum capacity reduction reaches 81.6%, with pronounced transitions around s/B = 1 and d/B = 1. Under deep burial, the principal failure surface remains predominantly a deep elliptical arc and capacity reduction is generally below 15%. Burial depth therefore controls the spatial overlap between the environmentally damaged zone and the anchor-bearing zone. The results provide a mechanical basis for post-drought crack inspection, uplift-safety reassessment, and burial-depth selection. Hydraulic infiltration, suction, moisture evolution, and rainfall intensity are outside the present model.