Qinli Zhang

The stability of slice drifts is critical to the safety and sustainability of mining operations. In underhand cemented backfill mining, slice drifts may be subjected to a special condition in which both the roof and sidewalls are composed of cemented backfill. Therefore, evaluating their long-term stability is of significant engineering importance. To analyze the time-dependent deformation of this special structure, the roof and sidewalls were idealized as a fixed-end beam and a fixed-end wall, respectively. Burgers creep compliance was then incorporated to derive time-dependent expressions for roof subsidence and sidewall convergence. The effects of slice-drift width, in situ stress conditions, and creep influence range on deformation were then analyzed. Subsequently, a three-dimensional FLAC3D 6.0 model incorporating the actual excavation, backfilling, and creep processes was established. The Mohr–Coulomb and Burgers constitutive models were used to investigate the evolution of stress and deformation in slice drifts with different widths. The results show that increasing the slice-drift width significantly increases the roof tensile stress and sidewall convergence rate. Under the extreme condition in which four adjacent drifts on both sides are excavated simultaneously, roof tensile stress concentration and drift deformation are further intensified. Considering both the roof tensile stress and the allowable convergence rate during the stable creep stage of the sidewalls, a slice-drift width of 5.0 m is recommended. Finally, field convergence monitoring was conducted at eight monitoring points in two slice drifts with widths of 4.8–5.08 m. The monitoring results show that the average convergence rates within this width range were lower than 0.25 mm/d, satisfying the stability requirement. These observations support the reasonableness of the numerical results and the recommended slice-drift width. The findings provide a reference for long-term stability assessment and width design of backfill-formed slice drifts in underhand backfill mining.

To address the issues of severe goaf collapse, difficulties in secondary extraction, and insufficient pillar stability encountered during the mining of high stopes north of Line 60 at the Dongguashan Copper Mine, this paper takes these high stopes as the research object. Based on an analysis of the engineering geological conditions, goaf failure characteristics, and current mining status in this area, a study on pillar stability and the mechanical behavior of combined mining is conducted. Given the susceptibility of pillars with high aspect ratios to bending instability, the secondary extraction pillar is simplified as a rod with fixed ends. A mechanical model for the triangular pillar’s stability is established, the critical instability equation is derived, and the influence of the reserved width on the pillar’s critical stress and safety factor is analyzed. Subsequently, based on the critical instability equation, the relationship between the reserved pillar width and critical stress is obtained to optimize the pillar dimensions. Simultaneously, to mitigate the adverse effects of primary stope collapse on secondary extraction, optimized schemes such as three-stope combined mining and two-stope combined mining are proposed. A mechanical model for combined mining is established based on the Protodyakonov’s arch theory to analyze the stress distribution characteristics of the surrounding rock in the goaf under different mining schemes. The calculated stress of the original rectangular pillar is 29.01 MPa. When the reserved width exceeds 4 m, the pillar safety factor becomes greater than 1.6, satisfying the stability requirement. In addition, three combined mining schemes were compared using Protodyakonov’s arch theory. The goaf spans of the three schemes are 40 m, 26.6 m, and 36 m, respectively. The results indicate that the two-stope combined mining scheme transfers the main roof load to the adjacent ore body and backfill, reducing the load borne by the barrier pillar and providing a better balance between safety and production efficiency. The proposed framework, integrating field goaf detection, pillar buckling analysis, reserved-width optimization, and combined mining comparison, provides a practical method for the stability control and secondary recovery of deep high stopes.

With mining operations worldwide comprehensively advancing the development of intelligent mines, mine digitalization has become an inevitable trend in the evolution of the mining industry. In this context, efficient and high-precision fracture identification has emerged as a critical prerequisite technology for achieving digital transformation in intelligent mining systems. However, severe environmental noise in deep mines and the limitations of standard pixel-wise loss functions, which ignore the geomechanical continuity of fractures, often lead to fragmented segmentation results. To address this, we introduce the existing SCSegamba architecture as an efficient feature extraction backbone and propose a novel Fracture Orientation Consistency Loss (FOCL) as our core optimization objective. By penalizing directional discrepancies between predicted and actual fracture networks, FOCL explicitly enforces geometric and topological continuity. We evaluated our framework on a custom dataset of 600 high-resolution images from deep underground roadways. The results demonstrate that the SCSegamba-FOCL framework effectively bridges discontinuous fine cracks in low-contrast zones. It achieves a superior Mean Intersection over Union (mIoU) of 85.67% and an F1-Score of 0.869, while maintaining a real-time inference speed of 38 frames per second (FPS) on edge hardware.

Tailings backfilling (TB) is widely recognized as an environmentally friendly and engineering safe technique to enhance mining efficiency. However, the heterogeneous particle distribution in TB slurry, also-named the segregation phenomenon, can significantly affect the mechanical strength of the backfill, especially under high goaf conditions. Therefore, elucidating the spatial distribution characteristics of particles during high-goaf filling has become a crucial research focus for improving the mechanical behavior of tailings backfill. A systematic experimental investigation was conducted in this study, incorporating the similarity principle, to analyze the migration behavior of backfill slurry particles and to clarify how the different backfill heights influence the spatial distribution of fine, medium, and coarse particles. The results indicate a clear vertical variation in PSD. Based on statistical analysis of samples collected from different backfill height experiments, coarse particle content increased progressively from the upper to lower layers (median: 16.2%, 23.6%, and 25.0%), while medium-sized particles remained relatively stable (37.0%, 37.3%, 37.0%). Fine particles dominated overall but decreased with layers (45.6%, 38.8%, 38.3%). Coarse particles tended to settle downward due to gravitational forces, whereas fine particles migrated upward. The distribution of medium-sized particles remained largely homogeneous. Fine and coarse particles were subjected to opposing driving forces. Meanwhile, particles maintained an approximately symmetrical distribution in the horizontal direction. Moreover, when the backfill height exceeded 800 mm, a notable intensification of stratification occurred, indicating a strong height-dependent transition in segregation behavior. In contrast, in the horizontal direction, the PSD showed no clear dependence on backfill height. These findings provide new insights into the mechanisms of particle segregation within backfill materials, offering a theoretical foundation and experimental support for optimizing PSD within the backfill body and elucidating the collapse mechanisms of high goafs.

With the depletion of shallow resources, the transition from open-pit to underground mining has become an inevitable trend in the mining industry. Although the vertical longhole stage fill mining method is efficient and safe, its second-step stoping blasting is prone to damaging the underlying strategic rare orebody. To quantify the protective effect of the protective layer, this study established a three-dimensional fluid–structure interaction (FSI) numerical model for explosives-rock-backfill interactions using the ANSYS/LS-DYNA platform, based on the case of a large polymetallic mine. Systematic simulations were performed for six protective layer thicknesses ranging from 0.5 to 3.0 m, analyzing the cross-media propagation and attenuation characteristics of blasting stress waves and their dynamic damage mechanism to the underlying orebody.The results indicate that the protective layer thickness is a core parameter controlling damage, showing a significant negative correlation with the peak stress and displacement of the orebody. When the thickness is less than 1.5 m, the orebody response exceeds its damage threshold, leading to irreversible failure. When the thickness is ≥ 1.5 m, the peak stress can be reduced below the orebody’s ultimate compressive strength (74.871 MPa), and the displacement response is confined within the slight influence range (0.1–0.3 mm), achieving effective protection. The study innovatively applied the "Post Line Contour Mode" post-processing technique in LS-PrePost to achieve precise quantification of stress gradients and accurate localization of damage boundaries, validating the critical protective thickness of 1.5 m. This research clarifies the buffering mechanism and protection standards of the protective layer, providing a theoretical basis and design reference for safe and efficient coordinated mining of mineral resources under similar conditions.

Phosphogypsum-based cemented paste backfill (PCPB) represents an effective solution for managing substantial accumulations of PG. However, its practical application is limited by excessive fluoride content and insufficient strength. To systematically investigate the influence of initial fluoride content on the hydration behavior, microstructures, and strength development of PCPB specimens, synthetic phosphogypsum was prepared using CaSO₄·2H₂O and NaF to eliminate impurity interference in this study. A series of specimens was designed with varying initial fluoride content (5–70 mg/L), sand-to-cement ratios (1:6, 1:8, 1:10), and concentrations (63 wt%, 65 wt%). Setting time, unconfined compressive strength, isothermal calorimetry, X-ray diffraction, and scanning electron microscopy were employed to elucidate the effects and underlying mechanisms of fluoride on PCPB performance. The results indicate that higher initial fluoride content markedly delayed setting and reduced early strength. Calorimetric analysis confirmed that fluoride postponed the exothermic peak and extended the induction period, primarily due to the formation of the CaF₂ layer on clinker particle surfaces, which hindered nucleation and hydration. The microscopic results further revealed that high fluoride content suppressed the formation of ettringite and C-S-H gels, resulting in more porous and loosely bonded microstructures. Leaching tests indicated that fluoride immobilization in PCPB specimens occurred mainly through CaF₂ precipitation, physical encapsulation, and ion exchange. These findings provide theoretical support for the fluoride thresholds in PG below which the adverse effects on cement hydration and strength development can be minimized, contributing to the sustainable goals of waste reduction, harmless disposal, and resource recovery in the phosphate industry.

Red mud (RM) is a strongly alkaline waste residue produced during alumina production, and its high alkali and fine particle characteristics are prone to cause soil, water, and air pollution. Phosphogypsum (PG), as a by-product of the wet process phosphoric acid industry, poses a significant risk of fluorine leaching and threatens the ecological environment and human health due to its high fluorine content and strong acidic properties. In this study, RM-based cemented paste backfill (RCPB) based on the synergistic curing of PG and ordinary Portland cement (OPC) was proposed, aiming to achieve a synergistic enhancement of the material’s mechanical properties and fluorine fixation efficacy by optimizing the slurry concentration (63–69%). Experimental results demonstrated that increasing slurry concentration significantly improved unconfined compressive strength (UCS). The 67% concentration group achieved a UCS of 3.60 MPa after 28 days, while the 63%, 65%, and 69% groups reached 2.50 MPa, 3.20 MPa, and 3.40 MPa, respectively. Fluoride leaching concentrations for all groups were below the Class I groundwater standard (≤1.0 mg/L), with the 67% concentration exhibiting the lowest leaching value (0.6076 mg/L). The dual immobilization mechanism of fluoride ions was revealed by XRD, TGA, and SEM-EDS characterization: (1) Ca²⁺ and F⁻ to generate CaF₂ precipitation; (2) hydration products (C-S-H gel and calixarenes) immobilized F⁻ by physical adsorption and chemical bonding, where the alkaline component of the RM (Na₂O) further promotes the formation of sodium hexafluoroaluminate (Na₃AlF₆) precipitation. The system pH stabilized at 9.0 ± 0.3 after 28 days, mitigating alkalinity risks. High slurry concentrations (67–69%) reduced material porosity by 40–60%, enhancing mechanical performance. It was confirmed that the synergistic effect of RM and PG in the RCPB system could effectively neutralize the alkaline environment and optimize the hydration environment, and, at the same time, form CaF₂ as well as complexes encapsulating and adsorbing fluoride ions, thus significantly reducing the risk of fluorine migration. The aim is to improve the mechanical properties of materials and the fluorine-fixing efficiency by optimizing the slurry concentration (63–69%). The results provide a theoretical basis for the efficient resource utilization of PG and RM and open up a new way for the development of environmentally friendly building materials.

Tunnel faces in underground mines, as the front line of mining, play an important role in both mine safety and mining intelligence. However, the engineering quality of tunnel faces is still evaluated based on visual observations by technicians, which cannot guarantee safety and real-time performance. Therefore, there is an urgent need for a more effective method to detect the quality of tunnel face engineering. In this study, a high-performance and accurate tunnel face segmentation model was developed by applying the YOLOv5-seg computer vision model to an underground mine. By optimizing a classic Chinese underground mine image dataset through Sobel preprocessing and improving the network structure of the YOLOv5-seg model using the SimAM module, good predictive performance was achieved for tunnel face segmentation, with values of 0.97, 0.89, 0.80, and 0.78, respectively, achieved for the pixel accuracy, Dice coefficient, mask intersection over union (IOU), and box IOU on the test set. And the performance of this model outperforms all YOLOv5 models and U-net in the same task of tunnel face segmentation. Model interpretation and visualization further demonstrated the positive effect of the SimAM module on the model, and, finally, the segmentation results were used to evaluate the tunnel face engineering. Overall, this study’s results provide a feasible, safe, and real-time method for accurately segmenting tunnel faces in underground mines and provide a reliable approach for data-driven applications of intelligent technology in mines in the future.

This study conducts a simulation analysis of the stability of tall and collapse-prone stopes at the Dongguashan copper mine, using the FLAC3D-3.0 software to investigate the stress distribution and deformation behavior of geological materials under different working conditions, providing an effective means of addressing complex mechanical issues in geotechnical engineering. In this paper, the stability of the tall stopes in the Dongguashan mining area was analyzed through numerical simulations using the FLAC3D finite difference method. First, a three-dimensional numerical model of the tall stopes was established based on the actual conditions of the mining area, simulating the mining conditions and environment. Next, the stress distribution, displacement variation, and potential instability zones under different mining schemes were studied, with a comparative analysis conducted between traditional mining methods and optimized schemes to clarify their respective advantages and disadvantages. Finally, based on the simulation results, the most suitable mining scheme for the area was identified, aimed at reducing the risk of stope collapse and improving the overall stability and safety of the mine. The findings provide technical support for the design and support of tall stopes in deep deposits and offer important reference points for mine safety management.