Bingchao Zhao

Traditional coal mining methods have led to prominent issues of coal resource waste and large-scale solid waste emissions. The integrated “excavation–backfilling–retention” mining technology for inter-section coal pillars and gate roads is one of the key technologies to solve these problems. However, the excavation and mining process associated with this technology imposes higher requirements on the ventilation system. Aiming at addressing the ventilation challenges existing during the implementation of the “excavation–backfilling–retention” method, research on ventilation safety assurance technology for inter-section coal pillars was carried out. Using COMSOL5.5 software, a full-stage ventilation system design model was constructed, adopting a ventilation mode that combines full-air-pressure ventilation with auxiliary local ventilation. The dynamic variation characteristics of the ventilation system under the “excavation–backfilling–retention” method and its capability to prevent and control the risks of O₂ and CO gas accumulation and coal spontaneous combustion were studied. The results show that during the bypass excavation period, the air supply from the auxiliary fan is sufficient, and during the excavation period for the two gate roads, due to the increased ventilation distance, insufficient airflow occurs near the heading face, accompanied by temperature rise, O₂ concentration decrease, and local CO accumulation, posing risks of coal spontaneous combustion and toxic gas accumulation. During the inter-section coal pillar excavation period and the cyclic operation period, after the full-air-pressure ventilation system is established, the airflow becomes stable, ventilation resistance decreases, and both temperature and gas concentrations are controlled within safe limits. However, in the corner areas, auxiliary local ventilation measures are still required due to insufficient O₂ and CO accumulation. The study verifies the feasibility and safety of the integrated “excavation–backfilling–retention” ventilation system, providing a safe ventilation approach for the integrated mining method and supporting the green mining of coal mines and the synergistic development of coal-based solid waste resource utilization.

Given the severe water hazard in the coal seam roof of the Binchang mining area, existing research methods still primarily rely on traditional approaches such as empirical formula and numerical simulation—resulting in insufficient accuracy and convenience in predicting the height of the water-conducting fracture zone (WCFZ). By comprehensively considering three influencing factors—mining thickness, mining depth, and working face length—a data-driven approach was employed to construct a multiple nonlinear regression prediction model and a Convolutional Neural Network (CNN) prediction model based on 27 sets of measured data. Both models were subsequently applied to the ZF1403 and ZF1405 working faces in the Yadian coal mine. The results indicate that when considering only single factor of mining thickness, the coefficient of determination (R²) value of the multiple nonlinear regression model was 0.64. When considering all influencing factors, R² improved to 0.84. The mean absolute percentage error (MAPE) of multiple nonlinear regression model was 7.52%. The established CNN model achieved a R² of 0.97, a root mean square error (RMSE) of 9.78, and a MAPE of 4.67%. Compared to the Back Propagation Neural Network model, the prediction accuracy of the CNN model was significantly improved. The relative prediction errors of the developed height of WCFZ in the ZF1403 and ZF1405 working faces at Yadian mine were 6.30% and 2.54% for the multiple nonlinear regression model, respectively, and 0.97% and 3.15% for the CNN model, respectively. Both models met practical engineering requirements. This paper can provide reliable technical support for the prediction of water-conducting fracture zone height under mining conditions similar to the Binchang mining area.

Transmission towers located above mined-out areas may experience collapse or instability due to mining-induced ground subsidence and deformation, which poses significant risks to the safe operation of power transmission lines. To clearly evaluate the deformation resistance and failure threshold of transmission towers under mining-induced ground deformation, this article examines a typical 220 kV self-supporting transmission tower located in a mining area of Northern Shaanxi Province through a detailed three-dimensional finite element model constructed and simulated using ANSYS 2022. The mechanical response and failure process of the tower structure were systematically simulated under five typical deformation conditions: tilt, horizontal compression, horizontal tension, tilt–compression, and tilt–tension. The results indicate that under individual deformation conditions, the critical deformation values of the tower are 35 mm/m for tilt, 10 mm/m for horizontal compression, and 8 mm/m for horizontal tension, demonstrating that the structure is most sensitive to horizontal tensile deformation. Under combined deformation conditions, the critical deformation values for the combined tilt–compression and tilt–tension conditions exhibited a marked reduction, reaching 8 mm/m and 6 mm/m. Compared to individual deformation conditions, transmission towers demonstrate a significantly higher susceptibility to structural failure under combined deformation conditions. The displacement at the tower head and the tower tilt angle exhibit a linear positive correlation with the values of ground surface deformation. Under individual deformation conditions, the tilt of the tower was approximately 0.903 times the tilt deformation value and 0.089 times the values of horizontal compression and tension deformation, indicating that tilt deformation exerts a more pronounced influence on the inclination of the tower. Under combined deformation conditions, the tilt of the tower reached approximately 0.981 times that of the tilt–compression deformation value and 0.829 times that of the tilt–tension deformation value. Compared to the tower tilt induced individually by horizontal compression or tension deformation, the tilt under combined deformation conditions demonstrated a significantly greater value. Under mining-induced ground deformation, a redistribution of support reactions occurs, exhibiting either nonlinear or linear increasing trends depending on the type of deformation. The findings of this article provide a theoretical basis and data support for disaster prevention and control, safety evaluation, and structural design of transmission lines in mining areas.

Compared with single coal seam mining, the stratum damage induced by shallow multi-seam mining is more severe and poses a risk of mine disasters that threaten the safety of coal mine personnel. In order to reveal the characteristics and mechanism of strata damage, in this paper, field measurement, numerical simulation and mechanical analysis are used to study the development characteristics and dynamic evolution laws of overburden and explain the dynamic evolution mechanism of a water-conducting fracture zone (WCFZ) and surface cracks. The height of the WCFZ to the mining height exceeds 31.68, which is higher than the empirical value of the study area. There are self-healing and activation laws for overburden fissures in shallow multi-seam mining, which is related to the hinge rotation of overburden and the deflection of the inclined structure. However, the maximum subsidence coefficient and crack angle of the surface induced by shallow multi-seam mining does not alter, but the complexity of surface crack activity increases. The dynamic development law of WCFZ is closely related to the breaking of key strata, while the dynamic evolution of surface crack is controlled by the form of surface block fracture instability and topography. In addition, a shallow multi-seam horizontal staggered mining model that is conductive to reducing surface damage is constructed, and a method has been proposed to lessen the risk of landslides brought on by surface cracks.

Fly ash–cement composite backfill slurry, prepared by partially replacing cement with fly ash, has been demonstrated to effectively reduce the mine backfill costs and carbon emissions associated with cement production. However, the use of fly ash often results in insufficient early and medium-term strength of the backfill material. To address the demand for high medium-term strength in backfill materials under continuous mining and backfilling conditions, this study developed a silica fume–fly ash–cement composite backfill slurry. The effects of varying silica fume contents on the slurry’s flowability, uniaxial compressive strength, microstructure, and pore characteristics were systematically investigated. The results showed that increasing the silica fume content significantly reduced the slurry’s flowability. However, at a silica fume content of 5%, the slurry achieved optimal medium-term strength, with a 14-day uniaxial compressive strength of 3.98 MPa, representing a 25% improvement compared to the control group. A microstructural analysis revealed that a moderate silica fume content promoted the formation of calcium silicate hydrate gel, filled micropores, and optimized the pore structure, thereby enhancing the overall strength and durability of the material. Conversely, an excessive silica fume content above 5% led to a marked decrease in both flowability and strength. Based on a comprehensive evaluation of silica fume’s effects on the flowability, strength, and microstructure, the optimal silica fume content was determined to be 5%. This study provides a theoretical basis and practical guidance for improving the efficiency of continuous mining and backfilling operations, and for designing high-performance backfill materials suitable for continuous mining and filling conditions.

This paper presents our study of the deformation and failure characteristics surrounding rock in roadways with super-large sections during the integrated coal pillar excavation, filling and retention process between coalfaces. Based on the theory of complex variable function, the mapping accuracy of conformal transformation is improved, and an analytical solution for surrounding rock stress in super-large sections of roadway is derived. The stress distribution law of the surrounding rock of rectangular roadways is analyzed, and numerical simulation software is used for supplementary analysis and verification. According to the research findings, the compressive stresses on two sides and the tensile stress on the roof of a rectangular roadway with super-large sections decreased with the increase in the side-pressure coefficient; however, when the side-pressure coefficient increased to a certain point, those two sides changed from a pressure-bearing status to a tensile force-bearing status, while the roof changed from a tensile force-bearing status to a pressure-bearing status. In these stress changes, all the stresses upon the surrounding rock of roadways were compressive stresses and the two critical side-pressure coefficient values were λ_up and λ_down. As the aspect ratio of the roadway increased from 1 to 9, its λup increased from 1.823 to 5.865 and its λdown increased from 0.549 to 0.888. When those side-pressure coefficients in the environment where a roadway is located exceed their critical values, tensile stress will take place on the roadway boundary and result in tensile failure, thus leading to instability in the roadway super-large section. The impact of the side-pressure coefficient upon the plastic zone range of roadway surrounding rock is greater than the impact of the roadway width. In order to secure stability in the surrounding rock of roadways with super-large sections during the excavation process, the side-pressure coefficient should remain around 1; in this situation, the plastic zone covers the smallest range and the relevant support work is the easiest. These research findings provide theoretical references for the excavation and support of roadways with super-large sections.

This paper aims to evaluate the severities and causes of ground surface building and cropland damages after coal mining in a better way, and to clarify the correlation between the damage assessment indexes that influence mining. Against the backdrop of multi-seam mining in certain coal mines in China, the estimated results of each displacement and deformation were analyzed using GIS technology. The damage range determined for each deformation index is divided according to the displacement and deformation combined with the virtue of damage judgment threshold. The damage ranges on the ground surface based on the comprehensive value of each displacement and deformation index were obtained through superimposing those ranges delineated by each displacement and deformation index, and the law on influence from displacement indexes upon various levels of damage was analyzed in a quantitative manner accordingly. The results showed that coal mining destroyed 14 buildings and a cropland area of 11.96 hm²; among them, building damage was only associated with displacement indexes E (horizontal deformation) and T (inclined deformation). Seven buildings were solely destroyed by T alone; five buildings were solely damaged by E; two buildings were damaged jointly by E and T; and, moreover, with the aggravation in building damage level, the proportion of building damage due to E decreased while the proportion of building damage under the same level due to T increased. Regarding cropland destruction, the damage due to T accounted for 33.48% while the damage jointly caused by W (Subsidence), E and T accounted for 30.45%. Moreover, the proportion of damaged cropland area due to inclined deformation T was positively correlated with cropland damage level. These findings can provide a reference for rational judgment regarding civilian building and cropland destruction on the ground surface after coal mining.

How to quantitatively characterise the impact of underground coal mining on the stability and slippage of loess slopes is a key problem in the evaluation of mining damage under loess slopes, but it is more difficult to study this problem under the impact of the particular mechanical properties and topographical features of loess slopes. In order to clarify the impact of underground coal seam mining on the stability and slippage of the loess slope, theoretical analysis, numerical simulation and physical similarity simulation experiments are used to address the problem based on the theory of slope stability and strata movement. The results show that the stability coefficient of a mining slope (K_ms) is introduced to quantitatively characterise the stability of a mining loess slope, and to measure the degree of landslide risk. Due to the superposition of slope movement caused by mining subsidence and slope sliding tendency, the slope is more unstable when mining along the slope than when mining against the slope. The slope angle and slope height are the most important factors influencing the K_ms. The ratio of rock stratum thickness to mining height and the ratio of rock stratum thickness to soil stratum thickness are positively correlated with K_ms, and the correlation is relatively strong. The range of variation of the volume weight, internal friction angle and cohesion of the loess is small, and the influence on K_ms is relatively weak. Probability integral theory is used to construct the relationship between stability and slippage of mining loess slopes. Taking the mining of a working face under the loess slope of Ningtiaota Coal Mine (China) as an example, the predicted results of the slope movement and deformation theory are in good agreement with the similar simulation test results, reaching 93.57~97.97%.

This study proposes a novel idea of the use of coal gangue (CG) activation and preheated decarburized activated coal CG-based cemented paste backfill material (PCCPB) to realize green mining. PCCPB was prepared with preheated decarburized coal CG (PCG), FA, activator, low-dose cement, and water. This idea realized scale disposal and resource utilization of coal CG solid waste. Decarbonization and activation of CG crushed the material to less than 8 mm by preheated combustion technology at a combustion temperature of 900 °C and a decarbonization activation time of 4 min. The mechanism of the effect of different Na₂SO₄ dosages on the performance of PCCPB was investigated using comprehensive tests (including mechanical property tests, microscopic tests, and leaching toxicity tests). The results show that the uniaxial compressive strength (UCS) of C-S2, C-S3, and C-S4 can meet the requirements of backfill mining, among which the UCS of C-S3 with a curing time of 3 d and 28 d were 0.545 MPa and 4.312 MPa, respectively. Na₂SO₄ excites PCCPB at different curing time, and the UCS of PCCPB increases and then decreases with the increase in Na₂SO₄ dosage, and 3% of Na₂SO₄ had the best excitation effect on the late strength (28 d) of PCCPB. All groups’ (control and CS1-CS4 groups) leachate heavy metal ions met the requirements of groundwater class III standard, and PCCPB had a positive effect on the stabilization/coagulation of heavy metal ions (Mn, Zn, As, Cd, Hg, Pb, Cr, Ba, Se, Mo, and Co). Finally, the microstructure of PCCPB was analyzed using FTIR, TG/DTG, XRD, and SEM. The research is of great significance to promote the resource utilization of coal CG residual carbon and realize the sustainable consumption of coal CG activation on a large scale.