Taoying Liu

Deep mining operations in metal mines face escalating challenges from high in situ stress environments, where conventional single-method ground control approaches often prove insufficient. This study proposes an innovative combined protection technology integrating four synergistic components: (i) prestressed rock bolt and plate support for immediate roadway reinforcement, (ii) hydraulic fracturing-based shielding to create fracture zones isolating the orebody from surrounding high-stress regimes, (iii) destress blasting at the orebody crown to form a stress-transfer barrier, and (iv) subsequent cemented paste backfill to provide long-term regional stability. Theoretical formulations are derived for each component: a bolt–rock composite bearing model quantifies the confinement provided by prestressed support; a fracture mechanics-based model characterizes the stress-shielding efficiency of hydraulic fracture networks; controlled blasting theory predicts the stress redistribution achieved through crown destressing; and a backfill arching model evaluates the long-term load-bearing capacity of cemented paste fill. A three-dimensional FLAC3D numerical model was established to simulate six working conditions: no protection, support-only, shield-only, pressure relief-only, backfilling-only, and the integrated four-component system combining support, shield, pressure relief and backfilling. The numerical results reveal that the integrated composite protection system reduces roadway subsidence by 86%. Furthermore, the synergistic effect among all components exceeds the sum of individual contributions, which verifies the necessity of adopting the comprehensive protection strategy under deep high in situ stress conditions. The research findings provide theoretical basis and engineering design references for safe and efficient mining in deep metal mines.

1. Freeze–thaw damage constitutes a pervasive threat to engineering infrastructure in cold regions across the globe, particularly at high latitudes and altitudes. The climatic conditions in these a...

Acoustic emission (AE) and digital image correlation (DIC) techniques enable real-time capture of damage signals and full-field deformation at anchored rock–concrete interfaces under shear loading, which is critical for quantitatively characterizing freeze–thaw (F-T) degradation and preventing geological disasters in cold regions. This study synchronously monitored full-shear-process AE signals using a broadband AE system (150 kHz resonant frequency, 5 MS/s sampling) and captured high-precision full-field deformation via a 5-megapixel monocular DIC system (25 fps). F-T cycle and direct shear tests were conducted on sandstone–concrete anchored specimens with varying F-T cycles and anchor depths to investigate their effects on shear mechanical properties, AE characteristics and failure modes. Results show that AE peak ring count first decreases by 44.9% then increases by 56.5%, while cumulative ring count exhibits a three-stage evolution. Shear crack proportion first decreases then increases, with tensile failure remaining dominant throughout. DIC reveals that F-T cycles shift failure from crack propagation to surface delamination and interface slip, while different anchor depths induce distinct failure patterns. This study confirms that AE and DIC can accurately characterize F-T degradation, providing a reliable non-destructive monitoring method for cold-region anchorage engineering.

To investigate the effects of freeze–thaw (F-T) action on the mechanical properties, pore structure, internal progressive damage evolution laws, and failure characteristics of initially damaged limestone, intact limestone specimens were subjected to different initial damage states and numbers of F-T cycles. Subsequently, the porosity and T₂ spectrum distribution of the specimens were tested using nuclear magnetic resonance (NMR). Finally, uniaxial compression tests were performed while monitoring the acoustic emission system. The test results showed that, as the number of F-T cycles increased or the initial degree of damage intensified, the peak strength of the limestone decreased, and the porosity increased. The higher the number of F-T cycles of limestone, the wider the distribution range of ringing counts in the middle and later stages of loading. As the number of F-T cycles increased, the proportion of tensile cracks in the limestone interior gradually increased and became dominant. The b-value evolution curves generally showed a sudden drop in the later loading stage. The damage variable of limestone did not show regular changes with an increase in the F-T cycles. This results from the superposition of the initial damage and the F-T cycles.

Conventional structural analysis of hinged precast frame beams (HPFB) often relies on a simplified load distribution method that may not fully account for deformation compatibility, potentially affecting result accuracy. To address this limitation, this paper develops a rigorous analytical framework based on the Winkler foundation model. The framework explicitly incorporates soil-structure interaction (SSI) and enforces static equilibrium and deformation compatibility at all structural nodes and hinges, thereby enabling a mechanically consistent prediction of structural responses. A comprehensive comparative analysis with a traditional frame beam (TFB) reveals the unique mechanical behavior of the HPFB system. Key findings demonstrate the HPFB configuration achieves a drastic reduction in maximum negative bending moment (63.5–83.5%) and shear force (7.8–22.8%), while increasing the maximum positive bending moment by 46–62%. This fundamental shift in internal forces occurs in conjunction with a characteristic segmented deflection profile. Sensitivity analysis further indicates that while the subgrade reaction coefficient significantly influences deflection patterns, its effect on bending moments and shear forces remains marginal. The proposed framework provides designers with a robust and theoretically sound tool for the analysis and design of HPFB structures, ensuring performance reliability while addressing limitations observed in current analytical approaches.

This study addresses the reliance on empirical methods in the structural analysis of hinged prefabricated frame beam (HPFM) structures by proposing a theoretically rigorous analytical framework based on the Winkler foundation model. The proposed analytical framework comprises three main steps: (a) The HPFB structure is discretized into individual beam segments supported on a Winkler foundation, based on the locations of anchorage points and hinge connections; (b) A system of linear equations is formulated using static equilibrium and deformation compatibility conditions at both anchorage points and hinge joints. Solving this system yields the distribution of concentrated loads—applied perpendicular to the slope surface at anchorage points—among horizontal and longitudinal beam segments of the cross beams, and simultaneously determines the shear forces transferred through hinge joints to adjacent beam ends; and (c) The deflection and internal forces for each Winkler-supported beam segment are evaluated using the computed loads and beam-end shear forces obtained in the previous step. To evaluate the validity and practical applicability of the proposed framework, a simplified HPFB structure was analyzed in terms of load distribution, beam-end shear forces, deflections, and internal forces. The results were compared with those from a traditional frame beam (TFB) structure under identical conditions to assess differences in mechanical behavior between the two structures. Deformation analysis at both the anchorage points and hinge joints indicates that the proposed analytical framework inherently satisfies deformation compatibility conditions at the anchorage points and hinge joints. Consequently, the results demonstrate improved accuracy compared to those derived from empirical methods. Comparative analysis reveals that, relative to the TFB structure, the HPFB structure exhibits larger deflections near the beam ends and smaller deflections in regions farther away from the beam ends, along with a reduced maximum negative bending moment, an increased maximum positive bending moment, and lower maximum shear forces. These results suggest that the HPFB structure offers improved mechanical performance. A sensitivity analysis was further performed to quantify the influence of the subgrade reaction coefficient on the mechanical behavior of the HPFB structure. As the subgrade reaction coefficient increases multiplicatively, the concentrated loads allocated to the shorter horizontal beam segments and their corresponding beam-end shear forces exhibit a progressive increase. Conversely, the loads assigned to the longer longitudinal beam segments and the associated beam-end shear forces demonstrate a consistent decrease.Variations in beam loading induced by a multiplicative increase in the subgrade reaction coefficient significantly influence beam deflection, yet exert only a minimal effect on both the bending moment and shear force. Consequently, the proposed analytical framework establishes a robust theoretical foundation for the rational design of HPFB structures, diminishing the dependency on empirical approaches and enhancing the reliability of structural performance predictions.

Understanding the intrinsic relationship between microscopic structures and macroscopic mechanical properties of rock under freeze–thaw (F-T) conditions is essential for ensuring the safety and stability of geotechnical engineering in cold regions. In this study, a series of F-T cycle tests, nuclear magnetic resonance (NMR) measurements, and uniaxial compression tests were conducted on sandstone samples. The mechanisms by which F-T cycles influence pore structure and mechanical behavior were analyzed, revealing their internal correlation. A degradation model for peak strength was developed using mesopore porosity as the key influencing parameter. The results showed that with increasing F-T cycles, the total porosity and mesopore and macropore porosities all exhibited increasing trends, whereas the micropore and different fractal dimensions decreased. The compaction stage in the stress–strain curves became increasingly prominent with more F-T cycles. Meanwhile, the peak strength and secant modulus decreased, while the peak strain increased. When the frost heave pressure induced by water–ice phase transitions exceeded the ultimate bearing capacity of pore walls, smaller pores progressively evolved into larger ones, leading to an increase in the mesopores and macropores. Notably, mesopores and macropores demonstrated significant fractal characteristics. The transformation in pore size disrupted the power-law distribution of pore radii and reduced fractal dimensions. A strong correlation was observed between peak strength and both the mesopore and mesopore fractal dimensions. The increase in mesopores and macropores enhanced the compaction stage of the stress–strain curve. Moreover, the expansion and interconnection of mesopores under loading conditions degraded the deformation resistance and load-bearing capacity, thereby reducing both the secant modulus and peak strength. The degradation model for peak strength, developed based on changes in mesopore ratio, proved effective for evaluating the mechanical strength when subjected to different numbers of F-T cycles.

In order to cope with the emergence of energy conservation and consumption reduction initiatives, we used an acrylic emulsion (as the adhesive), combined with silica aerogel (SA) and hollow glass microsphere (HGM) fillers, to synthesize thermal insulation coatings, which were found to have low thermal conductivity and excellent thermal insulation properties. These waterborne coatings are environmentally friendly and were synthesized without organic solvents. Comprehensive testing verified that the coatings met practical requirements. Specifically, the addition of 18% SA resulted in minimal thermal conductivity (0.0433 W/m·K), the lowest density (0.177 g/cm³), as well as a reduced gross calorific value. At a heating surface temperature of 200 °C, the 5 mm coating’s cooling surface temperature was 108.7 °C, yielding a 91.3 °C temperature difference and demonstrating remarkable thermal insulation performance. Furthermore, the coatings showed favorable results in terms of water resistance, corrosion resistance, wear resistance, and adhesion, achieving satisfactory engineering standards. In this work, the influence of different contents of SA on various properties of the coating was studied, with the aim of providing a reference for the modulation of the comprehensive performance of SA thermal insulation coatings.