Despite its abundance and technological maturity, coal imposes severe environmental and geological impacts during traditional extraction and use, including land subsidence, waste generation, and large CO₂ emissions that challenge sustainable development. Carbon-fixing backfill technology, integrating mineral carbonation with cemented gangue backfill, offers a promising pathway to emission reduction, carbon fixation, ecological restoration, and hazard mitigation. However, the mechanical performance and geological compatibility of carbon-fixing backfill, along with the carbon fixation capacity of the cementitious system have been overlooked, limiting practical implementation and development. Given its resource endowment, China relies on coal as its primary energy source and has set dual-carbon targets to ensure both energy security and emission reduction. As one of the world’s largest CO₂ emitters, the country faces substantial pressure to curb carbon emissions. We propose an in-situ conversion mining and carbon-fixing backfill approach, enabled by an intelligent unmanned mining machine, to achieve simultaneous CO₂ sequestration and large-scale disposal of coal-derived solid waste. Tailored formulations for varying gangue contents deliver tunable compressive strength (1.2–24.1 MPa), adequate fluidity, and net-negative carbon emissions of up to 145 kg CO₂/t. Life-cycle assessment and national scenario modeling show a sequestration potential of 133–315 Mt CO₂/yr and utilization of 191 Mt waste/yr. By targeting the core mining regions, this framework delivers a viable solution for low-carbon resource conversion, directly addressing the dual challenges of carbon mitigation and waste disposal.

Mining-induced seismicity is a distinct category of anthropogenic earthquakes, with their incidence increasing with mining depth. This study is grounded in mining-induced seismic data and technical solutions from typical mines in China. Mining-induced seismicity is defined as all detectable surface seismic motions within mining areas due to deep mining. This study first delves into the mechanisms of overburden breaking-type and fault slip-type mining-induced seismicity. The driving force is regional stress redistribution and concentration in the overlying strata. An integrated underground-surface monitoring network based on 4G/5G and GPS synchronisation is presented. The system’s data volume increased by 55.65%, and its validity increased by 198.29%. A hybrid algorithm integrating genetic algorithms with the Powell algorithm is developed to address challenges in source localisation. An evaluation model for monitoring efficiency is established, based on the Improved Non-Dominated Sorting Genetic Algorithm II. The evaluation of prevention technologies indicates that deep-hole blasting achieves significant efficacy by "replacing one major event with multiple minor events”. Overburden separation grouting has limited impact on energy release, and hydraulic fracturing remains inconsistent due to uncontrollable flow behaviour. This study contributes to an in-depth understanding of mining-induced seismicity, thus providing valuable references in the field of coal mine dynamic disasters.

To investigate the evolution of pore-fracture structure (PFS) in coal under stress constraints, real-time nuclear magnetic resonance tests were conducted on coal samples subjected to four stress paths (SP-I to IV). The PFS evolution, fractal characteristics, failure morphology, and permeability contribution were analyzed using T₂ spectra, nuclear magnetic resonance images (NMRIs), and fractal theory. The results show that stress paths significantly influence pore compaction, dilation, and fracture development. SP-III exhibits the most significant promotion of pore dilation before coal failure, followed by SP-IV and SP-II, whereas SP-I suppresses pore dilation. Confining pressure unloading promotes pore dilation, whereas the effect of axial loading depends on the confining pressure reduction. Coal failure significantly reduces pore heterogeneity, accompanied by a decrease in the pore fractal dimension (D_b). Multifractal parameters Da and A_c were associated with pore compression, dilation and microfracture nucleation, while H_c served as a robust index of pore connectivity. The failure mode of SP-I was shear-dominant, while the remaining stress paths manifested a combined tensile-shear failure. The failure zone of SP-III exhibited the highest morphological complexity, followed by SP-IV, SP-II, and SP-I. The stress path significantly influenced the permeability contribution of PFS within the 100–1000 ms, highlighting distinct permeability responses under different stress paths. These findings provide valuable insights into the mechanisms governing gas migration in coal seams.

Blasting remains the dominant rock fracturing method, yet its use is increasingly constrained by safety and environmental concerns. Soundless chemical demolition agents (SCDAs) offer a non-explosive alternative, yet conventional products are costly, rely on non-renewable raw materials, and require long fracturing times. Here, this study explored the use of two industrial wastes, calcium carbide residue (CCR) and drinking water sludge (DWS), to synthesize sustainable SCDAs (CCR-DWS SCDAs). CCR, which is rich in Ca-bearing phases, served as the precursor for CaO, the primary expansive component, whereas DWS provided Al-, Fe-, and S-bearing constituents that helped regulate the reaction process and improved the expansion performance. Results demonstrated that the optimal formulation (6% DWS and 30% water content) reached 37.11±1.42 MPa at 4 h and 50.45±2.55 MPa at 24 h, outperforming four commercial SCDAs. Microstructural characterization identified portlandite as the dominant phase responsible for crystallization-induced expansion. An appropriate DWS addition enhanced the expansive pressure by regulating the hydration kinetics, whereas excessive DWS suppressed the hydration reaction and impaired pressure development. Granite fracturing experiments further confirmed the superior efficiency, showing that the optimal CCR-DWS SCDA achieved crack penetration much earlier, within only 1.4 h at a borehole diameter-to-side length ratio of 1:5 and 8.8 h at 1:10, compared with 10.8 h and 18.8 h for the commercial SCDA. Fracture-surface characterization further revealed that the higher loading rate induced by the CCR-DWS SCDA produced smoother macroscopic fracture planes, supporting more controlled and predictable directional fracture propagation. Overall, this work establishes a waste-to-performance pathway for producing high-efficiency SCDAs with clear sustainability and engineering benefits.

This study investigates fluid injection-induced fault slip under true triaxial stress, focusing on cases where injection boreholes are either hydraulically connected or disconnected from the fault. Through stress and displacement monitoring, acoustic emission analysis, spectral and source mechanism inversion, and CT scanning, three stages of fluid injection-induced fault slip were identified: injection-induced disturbance, hydraulic fracturing, and pore pressure buildup within the fault zone. The results reveal the dynamic evolution of fracture initiation, pressure accumulation, and fracture propagation leading to fault slip, and show that the fault slip state significantly influences pressure buildup. The observations confirmed a poroelastic coupling mechanism: as pore pressure within the fault zone rises, slip velocity initially increases with the injection rate and subsequently decreases. Source mechanism analysis indicates that fault slip is dominated by compressive-shear motion, whereas hydraulic fracturing exhibits tensile-shear characteristics. Rock mechanical strength, permeability, and stress field evolution analyses showed that fault reactivation precedes hydraulic fracturing of surrounding rock in hard rocks, whereas hydraulic fracturing occurs before fault slip in soft rock. In addition, for low-permeability faults, direct fluid injection is more effective in controlling slip than that for high-permeability faults.

How inter-drawbell spacing dictates three-dimensional flow interactions and the formation of stagnant pillars under uneven drawdown remains a critical, unquantified challenge in block caving. To resolve this scientific problem, a multi-scale kinematic framework was established. Large-scale (1:33) physical drawing tests were conducted and utilized to rigorously calibrate a Discrete Element Method (DEM) model, analyzing granular flow dynamics across varying drawbell spacings (4, 6, and 8 m). To quantitatively decode complex spatial interactions, a novel data-driven framework based on the DBSCAN-a-shape algorithm was introduced, enabling the precise 3D morphological reconstruction of the Isolated Extraction Zone (IEZ). The integrated analysis revealed that the mass of stagnant pillars increases quadratically with spacing, governed by a determinable static equilibrium limit. Furthermore, the non-linear morphological evolution of the IEZ was strictly quantified, transitioning from an initial constrained ellipsoid to an unconfined "inverted trumpet” geometry. Based on the site-specific fragmentation profile (predominant 200–300 mm in-situ fragment size), a 6 m spacing was quantitatively identified as the optimal configuration to balance maximum flow efficiency with pillar stability. This research provides a new analytical paradigm and precise design criteria for multi-drawbell extraction.

To reveal the mechanical response characteristics of deep rock masses under the complete engineering disturbance chain of "stress loading, excavation unloading, support reinforcement, and cyclic disturbance,” this study employed a true triaxial testing system combined with acoustic emission monitoring to conduct rock mass failure tests under coupled loading–unloading-support-disturbance actions. Results indicate that unloading is the dominant factor inducing rock mass damage and degradation, reducing strength by 31.57% compared to static loading. The superimposed disturbance effect further decreases the strength by 17.40%. Support partially restored rock strength and stiffness, increasing them by 7.29% and 10.37%, respectively, compared with pure unloading. Unloading increased dissipated energy per stress increment, and support achieved a dual effect of "energy dissipation and damage suppression” by inhibiting repeated crack reopening. Along the undisturbed path, damage accumulated slowly early and then exhibits a concentrated late-stage jump. Under disturbance, damage followed an "increase during loading, gradual change during unloading, and sharp surge at failure” pattern, with a markedly smaller rise in the damage variable at final instability than under the undisturbed path. Under disturbed conditions, intact rock showed the Kaiser effect, whereas unloaded rock subsequently exhibited the Felicity effect, supporting delayed Felicity onset, enhancing stress memory and disturbance resistance.

To study the tensile failure mechanism of roof rock strata in deep water-rich mines, this paper conducts water immersion treatment and Brazilian splitting AE (acoustic emission) experiments on sandstone. Energy evolution characteristics, AE characteristics, and the constitutive relationship of sandstone are explored. During the loading process, the energy conversion of rock samples shows a stepwise evolution characteristic. In the initial loading stage, stable accumulation of elastic strain energy is accompanied by primary crack closure. It causes small fluctuations in dissipated strain energy. In the middle loading stage, stored energy keeps growing, and micro-crack adjustment makes the dissipated strain energy become stable. In the later loading stage, explosive expansion of new cracks leads to a sharp rise in dissipated energy in the stage, which is dominated by plastic deformation. When elastic strain energy approaches the storage limit, energy quickly releases through crack expansion and the kinetic energy of fragments. It causes overall instability of the samples. Water penetration remarkably changes the mechanical response mechanism of the samples. Mineral cementation weakening and particle interface loosening lead to a decrease in energy storage limit. Under water–rock interaction, expansion, and dissolution of clay materials lead to crack generation. Then, cracks make the rock’s energy storage capacity continuously decline with increasing immersion time. Besides, affected by water–rock interaction, the sample failure process shows a slower energy release rate. Meanwhile, their failure mode changes from brittle transgranular splitting to ductile intergranular splitting. This indicates that crack path adjustment, which is induced by water, effectively disperses local energy accumulation. It shows ductile failure features macroscopically. Dynamic evolution of AE signals and damage accumulation form a coupled response. In the initial stage, low-frequency signals are excited by particle friction and primary crack activities. Moreover, low-frequency signals become inactive as the energy-releasing rate slows down in the middle loading stage. Moreover, secondary crack penetration in the later loading stage triggers a sharp increase in high-frequency signals. For water-immersed samples, the crack expansion threshold decreases due to pore water pressure. Meanwhile, AE intensity weakens significantly. It reveals an internal mechanism that the water softening effect inhibits the generation of high-intensity pulses by reconstructing the energy release path. A constitutive model is proposed and verified by experiments. The proposed constitutive model can respond well to the mechanical behavior of water-immersed softening and the mechanical damage of the samples. Meanwhile, it can accurately predict the critical failure stress of samples. This study provides a theoretical basis for the stability evaluation of mine roof under complex hydrogeological conditions.

The split Hopkinson pressure bar (SHPB) technique is widely used to test the dynamic mechanical properties of materials. However, conventional three-wave and two-wave methods for processing SHPB data introduce reconstruction errors in the stress-strain curve due to the incomplete satisfaction of the uniform stress assumption, affecting accuracy, especially for materials like rock and concrete. This paper proposes a mean stress-based SHPB data processing method (MS method) that avoids these reconstruction errors. First, by analyzing the stress-strain formulations in conventional models using one-dimensional elastic wave theory, a novel stress-strain reconstruction model (MS model) is developed. Then, the theoretical self-consistency and reconstruction errors of the three models are evaluated, revealing the causes of reconstruction errors in the conventional models and the advantages of the MS model. Finally, a data processing method is then proposed by combining the MS model with an algorithm to estimate the specimen’s mean stress. Applying the MS method to the concrete specimen SHPB data processing not only reveals the reconstruction errors inherent in the conventional methods but also demonstrates the significant value of replacing them with the MS method in improving the accuracy and applicability of SHPB technique.

Rockbursts frequently occur during deep mining. They are catastrophic failures of the coal-rock composite (CRC); however, identifying their precursory signals remains challenging. This study presents a principal component analysis (PCA)-density-based spatial clustering of applications with noise (DBSCAN)-assisted workflow for warning-time analysis of CRCs. Conventional uniaxial and cyclic loading-unloading tests were conducted on CRC with four different roof rock lithologies. PCA was used to reduce redundancy among multiple acoustic emission (AE) parameters, and DBSCAN was used to organize AE samples in the reduced feature space for subsequent warning-time analysis. The results indicate an inflection point in the axial strain rate before failure, which may reflect a transition in the deformation state of the composite near the critical stage. AE signal evolution shows distinct stages, with AE count and AE energy rising sharply near failure. The PCA-DBSCAN-assisted workflow identifies different warning-related patterns: responses in the coal body are more dispersed and appear earlier, whereas responses in the roof rock are more concentrated closer to failure. The workflow provides a structured basis for organizing correlated AE responses and comparatively analyzing warning-related evolution in the coal body and the roof rock. Importantly, warning time is affected by roof lithology and generally appears earlier in the coal body than in the roof rock. These findings provide a laboratory-scale basis for comparative warning analysis of CRCs under different lithological conditions.

The microfine ilmenite generated during ilmenite beneficiation is challenging to separate from gangue. As a result, it is often discarded directly into tailings, causing wastage of titanium resources. In this study, 2-(hydroxycarbamoyl) decanoic acid (CBHA), a bifunctional collector with strong selectivity and high collecting capacity, was synthesized for the recovery of microfine ilmenite from tailings. When CBHA was used at a low dosage of 800 g/t, the concentrate with a grade of 47.70% and a recovery of 65.74% was achieved. Moreover, the adsorption mechanism was revealed by quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM), and density functional theory (DFT). The results showed that the adsorption amount of CBHA on the ilmenite surface reached 510.27 ng/cm² and the maximum adhesion force between ilmenite particles reached 22.62 nN, which were more than those on the forsterite surface. This is because the oxygen atoms of CBHA contributed electrons to match with three Ti or Fe sites on the ilmenite surface, resulting in a bicyclic adsorption configuration with an inner ternary ring and an outer polycyclic. In contrast, CBHA adsorbed on the forsterite surface via a single bond or monocyclic structure. In summary, this method promotes sustainable utilization of ilmenite and achieves economic benefits.