Zong-Tang Zhang

Roadway cross-sectional geometry dominates surrounding rock deformation and failure, yet most existing numerical studies adopt oversimplified ideal cavities rather than practical coal mine roadway profiles, lacking systematic comparisons of real engineering section shapes. This work aims to reveal how practical cavity geometries alter rock mechanical behaviors and fracture mechanisms under uniaxial compression. Twelve equal-area cavity models corresponding to four common underground coal mine roadway types (circular, arched, rectangular, trapezoidal) were constructed, and two-dimensional discrete element method (DEM) uniaxial compression simulations were performed. The results indicate that uniaxial compressive strength and elastic modulus continuously decrease as cavity shapes shift from smooth circular arcs to angular asymmetric profiles, with degradation aggravated by increasing sharp corners; cavity geometry exerts limited influence on Poisson’s ratio but enlarges surrounding rock radial displacement at sharp edges. Angular cavities trigger severe coupled tensile–compressive–shear stress concentration, advance microcrack nucleation and expansion, and generate broader X-type conjugate shear bands, significantly weakening rock bearing capacity. This study clarifies the mesoscopic stress evolution law of rock around roadways, offering theoretical support for roadway section optimization and surrounding rock disaster prevention in underground engineering.

Accurate identification and risk assessment of hidden defects in urban roads are essential for preventing road collapse and ensuring infrastructure safety. Based on a large-scale investigation of urban roads in Hunan Province, China, this study proposed a multi-scale collaborative detection framework integrating three-dimensional ground-penetrating radar (3D GPR) wide-area screening, manual interpretation, two-dimensional (2D) multi-frequency verification, and borehole endoscopic validation. Typical electromagnetic response characteristics of cavity, void, and loose-zone defects were summarized, and qualitative recognition criteria for different defect types were established. A total of 153 endoscopically validated defect cases, including 115 loose zones, 28 voids, and 10 cavities, were analyzed to investigate defect distribution and associated formation factors. The results show that underground pipeline damage, engineering disturbance, and inadequate backfill compaction are the main factors associated with defect development. Inadequate backfill compaction accounts for approximately 70% of all detected defects and is mainly related to early-stage defects, whereas pipeline damage is associated with nearly 90% of cavity cases despite accounting for only 30% of all cases. Risk assessment results show that cavities and voids are mostly high-risk defects, while loose zones are mainly moderate- to low-risk defects. The proposed framework provides a practical basis for subsurface defect identification, risk warning, targeted remediation, and preventive maintenance of urban roads.

This paper investigates the mechanical behavior of fiber-sand mixtures (FSM) by comprehensively examining the effects of fiber volumetric content (FC) and fiber length (FL) from both macroscopic and microscopic perspectives using the discrete element method (DEM). A hybrid digital photogrammetry and deep learning approach integrating YOLOv5 and U-Net is developed to rapidly identify particle contours and construct realistic shape databases for fibers and sand grains. Based on these databases, numerical biaxial compression tests are conducted on FSM samples with different FC and FL. The results show that increasing FC and FL significantly enhances the peak and residual stress ratios, leading to increases in peak and residual friction angles of up to 8.5% and 6.2%, respectively. Higher FC values also promote volumetric shrinkage, while longer fibers delay volume contraction by providing additional bridging and rotational restraint. Microscopic analysis reveals that increasing FC reduces sand-sand coordination numbers and increases sand-fiber contacts, while longer fibers contribute to a higher sliding contact ratio and improve internal stability by restricting particle rearrangement. The findings elucidate the micro-mechanisms governing strength improvement and deformation behavior in FSM and provide guidance for optimizing fiber reinforcement strategies in geotechnical engineering applications.

Due to the widespread prevalence of respiratory diseases such as COVID-19 and H1N1, the use of disposable masks has increased significantly. Consequently, the environmental issues arising from their accumulation have become increasingly severe. This study, therefore, aims to investigate the potential of using masks as soil reinforcement materials. This study conducted triaxial and seepage tests on mask–calcareous sand mixtures with varying ratios to examine the effects of mask content on the strength, modulus, particle fragmentation, and permeability coefficient of calcareous sand, as well as the influence of different mask sizes on shear strength and shear dilation. The results demonstrate that with an increase in mask content, the peak stress ratio of the mask–calcareous sand mixture increases by 4% per level, and the internal friction angle rises by approximately 1.6% per level. Conversely, water permeability and shear swelling are reduced, and particle loss decreases by over 70%. The reinforcing effect of the mask is attributed to the high friction between the mask and the calcareous sand at the contact interface, which restricts the movement of soil particles during deformation, thereby enhancing the overall strength of the mixture. Among the three mask sizes, the smallest mask–calcareous sand mixture exhibited the greatest improvement in shear strength, and the shear shrinkage effect was more pronounced. This indicates that particle size also significantly influences the mechanical properties of the mixtures. The reinforcing effect of the mask on the soil results from the high friction at the interface between the mask and the calcareous sand. When the soil deforms, the mask enhances the overall strength of the mixture by restricting the movement of soil particles. Considering the impact of masks on the performance of calcareous sand, it can be concluded that the optimal mass content of masks is 0.3%. This study offers a new perspective on the reuse of discarded masks in civil engineering applications.

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.

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.

Traffic cyclic loading is the key factor that leads to the deterioration of the long-term service behavior of subgrade. A series of cyclic triaxial tests was carried out by the large-scale dynamic and static triaxial apparatus (LSDSTA) to study the dynamic behaviors of coal gangue subgrade filler (CGSF) under multi-step cyclic loading using the morphological characteristics of hysteretic curves (MCHC). MCHC was quantitatively characterized by four parameters, i.e., the unclosed degree (ε_phl), inclination of long axis degree (k_hl), area (S_hl) and fullness degree (α_hl). With the increase of dynamic strain, ε_phl increases exponentially. k_hl of the coal gangue sample first decreases and then shows an increasing trend with the increasing dynamic strain. The values of S_hl are close to each other, and the energy dissipation in the sample is small. However, with the increase of dynamic strain, the specimen failure degree is increased, S_hl increases exponentially, and the damping ratio increases. With the increase of dynamic strain, α_hl increases approximately linearly. Confining pressure has a certain effect on the four parameters. There parameters can be recommended and used for quantitative analysis the dynamic behaviors of subgrade filler under traffic cyclic loading.