Baoliang Zhang

1. Coal-bearing strata commonly comprise alternating coal and rock layers, including coal–rock and rock–coal–rock composite structures. Their mechanical integrity is strongly affected by bedding pl...

Traditional underground backfill mining generally faces persistent bottlenecks such as insufficient filling material supply, high transportation costs and low filling efficiency. As an emerging green mining technology realizing in situ backfill material self-sufficiency, cut-and-fill mining provides an effective solution to the above problems, but the influence mechanism of its key geometric parameters on engineering performance remains unclear, restricting standardized parameter design and field promotion. Taking a shallow-buried coal mine in Ordos as the engineering background, this study carries out physical similarity simulation tests to systematically investigate the evolution laws of overburden displacement and stress distribution under three controlled scenarios: a baseline condition (4 m mining thickness, 10 m filling width), reduced mining thickness (2 m, 10 m), and increased filling width (2 m, 15 m). The results show that mining thickness acts as the dominant factor governing the strata control effect: when mining thickness is reduced from 4 m to 2 m, the maximum vertical displacement at the 10 m survey line decreases by 53.8%, the coal pillar stress concentration factor drops significantly, and the main roof maintains structural integrity without large-scale fracture. Increasing filling width enhances the bearing capacity of gangue pillars and restores filling zone stress closer to the in situ level, but tends to induce separation fractures in higher strata. Overall, the strata behavior of cut-and-fill mining presents distinct zoning characteristics, with high-position strata movement transitioning to coordinated integral deformation instead of severe separation and fracture. The findings provide an experimental basis and design reference for geometric-parameter optimization and engineering application of gangue backfill materials in underground mining.

In this study, a dual-activated ternary composite material was prepared using red mud, fly ash and cement as the main cementitious components under a high red mud content to expand the resource utilization pathways of red mud and achieve improved performance of red mud–fly ash–cement-based geopolymers. The resulting workability, mechanical properties, and microstructural evolution for the developed composites were systematically investigated. The results show that Ca2+ and OH⁻ released from cement hydration increased the alkalinity of the cementitious matrix, while the chemical activator further promoted the dissolution of reactive Si and Al from red mud and fly ash, facilitating the formation of abundant C-(A)-S-H gels, thereby developing a continuous and dense cementitious network. The early strength was mainly provided by cement hydration, whereas the middle- and late-age strengths were governed by the pozzolanic reaction of fly ash, the continued hydration of residual cement clinker, and the formation of gel, crystalline, and particulate reaction products. When the cement content was reduced to 17.6% in the dual-activation system, the resulting composite had a slump of 213 mm, indicating good flowability for pumping. Also, the 3-day and 28-day compressive strengths reached 1.73 MPa and 3.01 MPa, respectively, satisfying the application requirements of filling materials with relatively high strength grades. When the cement content was reduced to 14.7%, the composite achieved a 28-day compressive strength of 2.16 MPa, indicating its potential suitability for low-strength non-structural filling and backfilling applications rather than load-bearing structural applications. Microstructural analyses further confirmed that the dual-activation system could promote the extensive formation of reactive C-(A)-S-H gels, with relatively uniform elemental distribution within the gel phase and a denser microstructure. This study provides a new approach for the large-scale utilization of red mud and proposes a composite mix design with the advantages of solid-waste recycling and low cement consumption, while promising engineering applicability.

Laser powder bed fusion (LPBF)-fabricated 316L stainless steel (316L SS) is constrained by its single γ phase structure, which limits further improvements in yield strength (YS). In this study, Ti and Al were introduced into 316L SS powder through in situ alloying. Taking advantage of the ultrafast solidification characteristics of LPBF, a multiscale hierarchical heterogeneous dual-phase structure was constructed, consisting of ultrafine α phase, network-like γ phase, and dispersed nanoparticles. The effects of the Ti/Al ratio on phase constitution, grain morphology, and mechanical properties were systematically investigated. The results show that the synergistic addition of Ti and Al profoundly alters the solidification pathway. As strong ferrite stabilizers, Ti and Al promote the γ to α phase transformation. In addition, Ti facilitates the columnar-to-equiaxed transition by forming nanoscale Ti(C, N) particles and suppresses grain growth through solute drag, resulting in significant grain refinement. By optimizing the Ti/Al ratio, the 1.6Ti7Al alloy developed a hierarchical heterogeneous structure in which the ultrafine α phase serves as a strengthening skeleton and the network-like γ phase provides ductile deformation pathways. During deformation, this architecture induces a pronounced hetero-deformation-induced strengthening effect. Together with grain-boundary strengthening and nanoparticle strengthening, the alloy achieves an excellent combination of mechanical properties, including a YS of 1102 MPa, an ultimate tensile strength of 1200 MPa, and a fracture elongation of 25.5%. This study provides a new design paradigm for developing high-performance hierarchical heterogeneous metallic materials using additive manufacturing.

Vertically loaded anchors (VLAs) are widely used as mooring foundations in marine environments. Their working conditions typically involve deep-sea seabed, frequently subjected to cyclic loads induced by wind, waves, and currents. Therefore, understanding the mechanical properties of VLAs under cyclic loading is essential for ensuring the safety of mooring systems. This paper summarizes the current research status on the mechanical properties of VLAs under cyclic loading, analyzing the mechanisms by which cyclic loads affect these properties. Additionally, it reviews and summarizes the research methods applied to studying VLAs under cyclic loading, discussing the issues inherent in various methodologies. Finally, it provides an outlook on future research into VLAs under cyclic loading, laying the groundwork for subsequent studies on the bearing mechanisms of novel VLAs, such as the double-plate vertically loaded anchor (DVLA), under cyclic loading.

Jinan City in China is known for its abundant spring water, and the protection of underground spring water transport channels is a key issue that needs to be paid attention to in Jinan subway construction. In areas where underground spring water transport channels are easily disturbed, when the shield tunnel passes through a composite formation with a permeable layer in the middle and an impermeable layer in the upper and lower parts, the underground spring water transportation channel is blocked, the spring veins are damaged, and the underground spring water is blocked in the upstream, resulting in an increase in the water pressure difference on both sides of the tunnel. In this paper, based on the working principle of a new type of pipe segment with a diversion function, a diversion function pipe model test box is designed and fabricated. Using this model box, the working state of the diversion function pipe segments is simulated. An earth pressure box and pore water pressure gauges are embedded in the model box to measure the earth pressure and pore pressure around the pipe under seepage unsymmetrical pressure. Strain gauges are attached in a circular shape on the inner side of the pipe to measure and calculate the strain and stress of the pipe. Through model tests, the effective repair of the diversion pipe on blocking groundwater flow and the relief effect of the unsymmetrical pressure of the pipe are verified.

This study employs similar simulation testing and discrete element simulation coupling to analyze the failure and deformation processes of a model coal seam's roof. The caving area of the overburden rock is divided into three zones: the delamination fracture zone, broken fracture zone, and compaction zone. The caving and fracture zones' heights are approximately 110 m above the coal seam, with a maximum subsidence of 11 m. The delamination fracture zone's porosity range is between 0.2 and 0.3, while the remainder of the roof predominantly exhibits a porosity of less than 0.1. In addition, the numerical model's stress analysis revealed that the overburden rock's displacement zone forms an 'arch-beam' structure starting from 160 m, with the maximum and minimum stress values decreasing as the distance of advancement increases. In the stress beam interval of the overburden rock, the maximum value changes periodically as the advancement distance increases. Based on a comparative analysis between observable data from on-site work and numerical simulation results, the stress data from the numerical simulation are essentially consistent with the actual results detected on-site, indicating the validity of the numerical simulation results.

Various methods of longwall full mining with partial filling have been extensively researched to satisfy the specific mining needs of pressurized-coal and residual-coal resources. This study introduces three longwall partial-filling-mining techniques: room–pillar filling mining, parallel-strip filling mining, and vertical-strip filling mining. Numerical simulations are employed to evaluate the efficacy of these methods. The findings indicate that vertical-strip filling mining results in minimal surface deformation and a more uniform distribution of displacements. In practical operations, the effectiveness of filling largely depends on the choice of filling technology and materials. The research further includes an optimization analysis of the filling technology, emphasizing the composition of the coal-gangue-paste filling system and the refinement of its components. Additionally, the study aims to explore the optimization analysis of filling materials, specifically focusing on performance-optimization methods. The experimental results illustrate that optimizing the filling materials can enhance the performance of filling paste, improving both early-stage and long-term compressive strength. Moreover, the paper examines the quantitative characterization of paste-filling-mining subsidence at various stages in conjunction with theoretical knowledge. Subsequently, mining-subsidence-control measures are recommended to address the primary deformation factors across different stages. Through an in-depth examination of filling-method designs, enhancements in filling technology, and predictions regarding filling-mining subsidence, this research offers valuable insights for optimizing longwall partial-filling-mining methods.