ABSTRACT Floor extraction roadway crossing layer drilling is a pivotal strategy for gas control in areas prone to coal and gas outbursts. However, this method often fails due to overburden pressure and mining stress, causing floor deformation and drilling blockage. To solve the problem for extracting gas of crossing coal layer drilling in the floor roadway, uniaxial compression tests on perforated specimens was carried out. And the plastic zone failure of crossing layer drilling was analyzed through numerical simulations in FLAC3D with customized command flow. The study finds that drilling angle, drilling section, and coal‐rock interface most affect borehole deformation. Hole sections show decreasing compressive strength: borehole mouth > borehole body > borehole bottom. The present investigation reveals that low dip angle drilling is particularly susceptible to complications such as borehole blockage and collapse. It is recommended to implement protective measures for low dip angle drilling.

The roof caving characteristics of the mining face significantly influence gas migration in old goafs, underground tunnel excavation, and the stability of surface structures. The mining length and the width of the retained coal pillar are crucial parameters affecting roof deformation and caving. By fabricating irregular-shaped specimen with varying mining lengths, conducting uniaxial compression tests, collecting defor-mation data using acoustic emission and VIC monitoring systems, and performing numerical simulations with ABAQUS, the mechanical properties and deformation characteristics of these irregular-shaped specimen were re-vealed. The findings indicate that: (1) Under uniaxial compression, the peak stresses of specimens with mining lengths of 50 mm, 60 mm, 70 mm, and 80 mm were 14.166, 9.738, 7.160, and 6.524 MPa, respectively. As the mining length increased, the peak stress of the specimens gradually decreased, with the rate of decrease slowing down. (2) The ring count and cumulative ring count of acoustic emissions exhibited distinct stage characteristics under uniaxial compression. The cumulative ring count decreased with increasing mining length of the irregular-shaped specimen, indicating a reduction in the internal damage area. (3) The ABAQUS numerical simulation results demonstrate that an increase in vertical loading stress leads to the gradual expansion of the plastic zone. When the proportion of the plastic zone is similar, the stress decreases with increasing mining length, suggesting that a longer mining length reduces the bearing capacity. Additionally, there is a linear decrease in both peak strength and the proportion of the plastic zone. The research findings can serve as a reference for studies on the failure mode and mechanical properties of roof caving in mining faces.

With the development of deep Earth engineering, the stability of surrounding rocks subjected to high temperatures from fire hazards has become an increasingly prominent issue. Therefore, studying the physical and mechanical properties of rocks under different thermal treatment modes is of great significance for the design of underground engineering. Taking red sandstone as the research object, this paper conducts physical parameter tests, uniaxial compression tests, and X-ray diffraction (XRD) on specimens under real-time high temperatures and natural cooling in the range of 600-1000 degrees C, to analyze the variations in specimen composition, the correlation between physical and mechanical properties and temperature, and to explore the underlying mechanisms. The results show that under both real-time high temperatures and natural cooling, the volume of sandstone increases while the mass decreases with rising temperature. At 1000 degrees C, the volume expansion rates are 3.30% and 3.80%, and the mass loss rates are 6.30% and 5.60%, respectively. Mechanical parameters, including peak strength, elastic modulus, and peak strain under the two treatments, all deteriorate significantly compared with those at room temperature. At 1000 degrees C, peak strength decreases by 54.83% and 36.26%, elastic modulus decreases by 74.55% and 67.96%, and peak strain increases by 65.63% and 43.75%, respectively. High-temperature-induced changes in the internal mineral structure and composition of sandstone are the main causes of rock mechanical property deterioration. During the cooling process, thermal shrinkage and recrystallization of mineral particles densify the rock structure; therefore, the compressive strength of naturally cooled sandstone is higher than that under real-time high temperatures. This study can provide theoretical guidance for the repair and reinforcement of rock engineering after high-temperature action.

To investigate the deterioration of compressive property of traditional concrete in a high-temperature environment, uniaxial compression tests were conducted on concrete at various high temperatures. Combined analytical techniques-scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric-mass spectrometry (TG-MS)-were used to analyze the degradation mechanism. The experimental results indicate that high temperature has a strong temperature-dependent effect on concrete's compressive strength. As temperature increases (400 degrees C, 600 degrees C, 800 degrees C), concrete's compressive strength decreases. These decreases are 27.52%, 56.6%, and 80.76% relative to room temperature, respectively. This phenomenon is attributed to the direct link between concrete's microstructure and its macroscopic mechanical properties-driven by thermal stresses generated during heating and the decomposition of cement hydration products. Temperatures above 400 degrees C trigger microcrack formation, and microcracks propagate more rapidly with increasing temperature. At temperatures further increasing to 600 degrees C, fewer cementitious materials are left decomposable; even stable calcium carbonate starts to decompose. At temperatures of 800 degrees C or more, decarburization occurs, rendering the concrete microstructure loose and porous. Partial separation of aggregates from the paste causes a near-total loss of compressive strength.

To investigate the dynamic response and failure mechanism of tempered glass subjected to falling-ball impact, a controlled falling-ball impact experimental platform was established. Strain gauges were arranged at multiple locations on the glass surface to capture the transient strain responses under different impact conditions. Based on the experimental setup, a finite element model of tempered glass was developed using Abaqus to simulate the impact process and stress-wave propagation behavior. The experimental results show that falling-ball impact induces pronounced transient strain responses in tempered glass, with strain amplitudes decreasing as the distance from the impact center increases. The strain responses also exhibit clear vibration attenuation characteristics due to energy dissipation and boundary effects. The numerical simulation results are in good agreement with the experimental strain-time history curves in terms of peak strain, temporal evolution, and attenuation trends, confirming the reliability of the numerical model. Further analysis indicates that stress waves generated at the impact point propagate radially within the glass plate and undergo reflection and superposition at the boundaries, leading to localized stress amplification. When the impact energy exceeds a critical threshold, the induced stress surpasses the strength limit of tempered glass, resulting in structural failure. The findings provide theoretical and experimental support for the impact-resistant design and safety assessment of tempered glass.

Fire can cause thermal stresses within concrete, causing irreversible damage to structure, which in turn reduces load-bearing capacity of concrete. To better protect concrete, high-temperature simulation tests on various parts of axially loaded concrete specimens are required to assess their performance and degree of damage in a fire, allowing for development of more effective protective measures. This study experimentally gets real time high temperature stress-strain curves of concrete and then uses a particle flow code to build a model that matches macro and microstructural features of concrete. The software was used to simulate damage to each part of pressurized concrete specimen when it was fired on 1 or 4 sides. The results reveal that number of cracks created by both heating modes rises with rising temperature, as well as with decreasing simulation position. This number is 137 and 915 at the down part of concrete specimen (DC). The 4 sides heating mode reduces pressure-bearing capacity of specimens and subjects the substructure to greater stresses, with a stress difference of 25.54 MPa at DC. The 1 side heating mode, despite its low heat transfer, subjected the substructure to unequal stresses, resulting in a broad low-stress zone with a stress difference of 25.18 MPa at DC. The 1 side heating method causes concrete specimen to tilt towards heating surface, compromising overall safety of structure. So, DC location should be carefully shielded by thermal insulation, and prevented from forming specimens that could catch fire on one side. This study contributes to a better understanding of fire damage to concrete specimens and provides more precise theoretical guidance for concrete specimen protection, hence better protecting building safety.

Abstract The application of liquid nitrogen ( LN 2 ) fracturing offers a promising thermofluid approach for improving the permeability characteristics of hot dry rock (HDR) reservoirs during geothermal resource development. Unlike conventional hydraulic fluids, LN 2 rapidly vaporizes at − 196 ° C , inducing steep thermal gradients, intense thermal stresses, and phase transition effects that strongly interact with the rock matrix. Uniaxial compression coupled with Brazilian splitting characterization was executed within this research, utilizing granite specimens following sequential exposure to elevated thermal conditions and subsequent LN 2 - induced cryogenic treatment. Granite specimens were subjected to heating at varying temperature levels, followed by exposure to LN 2 , with their responses evaluated using uniaxial compression and Brazilian splitting tests, ultrasonic velocity measurements, acoustic emission (AE) monitoring, and surface profilometry. Notably, under the 400 ° C + LN 2 condition, the reductions in mass and density ( Δ M and Δ ρ ) increased by 21.5 and 17 times, respectively, compared to the 25 ° C + LN 2 condition. Similarly, the reduction in P - wave velocity ( Δ V p ) was amplified by a factor of 10.5. Maximum declines in uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) reached 30.58% and 50.3%, respectively. The observed stress thresholds indicated that elevated temperature gradients induced substantial thermal stress, resulting in initial microstructural damage. The combination of higher thermal stress and LN 2 cooling accelerated microcrack development, as evidenced by distinct acoustic emission patterns. Under the 400 ° C + LN 2 condition, the quiet phase of acoustic emission ringing counts was shortened by 54.3%, and the onset of the rapid decline phase of the r - value occurred 13 seconds earlier than under the 25 ° C + LN 2 condition.

Coalbed methane (CBM) extraction plays a dual role in ensuring the safety of coal mines and enriching clean energy resources. The extraction radius of CBM boreholes is influenced by multiple factors, but the interactions of the factors and their relationships with the extraction radius remain unclear. Therefore, the effective extraction radius under varying factors was simulated using COMSOL, and the major factors were determined through sensitivity analysis and response surface methodology. Further, the relationships between the main factors, their interaction effects, and the extraction radius were studied, and a calculation model was constructed. The results indicate the following. (1) The factors are ranked in a descending order of their influence on the effective extraction radius as follows: initial gas pressure, coal thickness, initial permeability, extraction time, borehole radius. Specially, the initial permeability and drainage time have comparable levels of impact. However, the negative pressure and vertical stress exhibit weak impacts. Notably, the effective extraction area always presents a vertically expanding oval-like shape, and the thinner the coal seam, the shorter the contours that appear in the coal seam, and the smaller the curvature of the contours. The intuitive manifestation in the coal seam is that the pressure contour gradually changes from an arc to a straight line. (2) Significant interactions exist between the initial gas pressure and the initial permeability, as well as between the initial gas pressure and extraction time. Moreover, these interactions manifest as the increased initial gas pressure significantly inhibiting the impacts of the initial permeability and extraction time on the extraction radius. (3) The effective extraction radius of the group F 16-17 coal in the same mine was calculated as 4.98 m using the established model, which closely aligns with the measured value of 5 m.

For the study of the layout of the roadway in the coal pillar and floor strata co-mining working face at the Zhaogu No.2 mine, a mechanical model of the segmental coal pillar within the working face was established through theoretical calculations. The analysis considered the stress state of the coal pillar area under different collapse conditions in the goaf after upper strata mining. Additionally, FLAC3D numerical simulation software was used to simulate the stress distribution in the roadway for different layout positions during strata mining, thereby clarifying the impact of working face mining on the side roadway of the segmental coal pillar. The results show that the collapse of the goaf after upper strata mining significantly affects the stress distribution in the coal pillar area. To ensure safety during mining, roadway excavation and working face recovery should be conducted after the upper strata have fully collapsed during strata mining. The co-mining working face roadway should be positioned beneath the original upper strata goaf, avoiding stress concentration areas in the coal pillar location. Ultimately, it is determined that the side roadway for the lower strata working face should be arranged with an offset of 10 m outward. Practical on-site experience has demonstrated that under this offset, there is minimal deformation of the surrounding rock in the coal pillar side roadway, meeting the safety production requirements of the working face.

This study addresses hydraulic support resistance determination in deep coal pillar caving faces at Zhaogu No. 2 Mine through integrated theoretical, numerical, and field analyses. Theoretical calculations (empirical estimation: ≥ 15.742 MN; dynamic load coefficient: ≥ 10.975 MN) and a "cantilever beam-masonry beam" composite mechanical model (≥ 16.029 MN) defined the resistance range. Numerical simulations revealed progressive coal pillar stress increase during mining, with stress transitioning from bimodal to unimodal distributions due to superimposed abutment pressure and open-cut stress. Complete pillar failure at 5 m from the open-cut reduced roof capacity, while roof displacement analysis identified 1.8 MPa (16.569 MN resistance) as optimal support intensity. Similarity model experiments validated stress field consistency under 1.8 MPa, confirming effective roof control. Field implementation of ZF18000/21/38D supports demonstrated normal resistance distribution during operation, aligning with theoretical predictions. This framework offers critical guidance for deep coal pillar face support design.

To achieve rapid freezing of the coal body in the step during rock cross-cut coal removal by freezing method, coal thermal conductivity with different water capacities at varying freezing temperatures is experimentally tested, and the hyperbolic model of thermal conductivity is proposed. The model parameters are optimized using the artificial neural network (ANN) method, and the model can mimic the change rule about thermal conductivity with temperature during the freezing process. Meanwhile, the time-varying law during the freezing process of the coal body is numerically analyzed using the thermal conductivity hyperbolic model and heat conduction theory; simulation results are analyzed and compared with measured results. After optimizing three parameters of the thermal conductivity hyperbolic model with the ANN approach, the calculated thermal conductivity values are distributed on a 1:1 line with measured results. This indicates that combining heat conduction theory with the thermal conductivity hyperbolic model can accurately predict the time-varying characteristics of temperature during the freezing process of the coal body with moisture content. Moreover, when coal body water capacity is about 12

The study of landslide dynamic process and impact intensity is of great significance to the qualitative and quantitative evaluation of landslides. This paper takes the Wangjiayan landslide as an example, establishes a more reasonable three-dimensional model based on high-precision DEM data, and uses PFC numerical simulation software to simulate the motion process and impact process of the landslide, respectively. By monitoring the characteristic parameters such as landslide velocity, displacement, energy, and impact strength, the dynamic features, energy conversion, and impact strength are linked to enriching the mechanism explanation of landslide dynamic features. The results show that the motion process of the Wangjiayan landslide lasted 34s, the main sliding time was 20s, the maximum displacement of the slide body was 358 m, and the maximum velocity appeared at 10s, which was about 24 m/s. During the landslide motion, the gravitational potential energy was mainly converted into collision and friction dissipation energy. According to the coordination of the slide body during movement, the Wangjiayan landslide can be roughly divided into four phases, namely, the chaotic phase of initial start-up, the coordinated phase of acceleration, the chaotic phase of high-speed steering, and the coordinated phase of deceleration, and the high-speed steering chaotic phase is the critical stage of energy dissipation. The impact strength at the foot of the slope is up to 2.4 × 1010 N. Both the impact strength and the final earth pressure decay exponentially with the increase of the distance from the rigid retaining wall to the foot of the slope.

Compared with insulating glass, tempered vacuum glass (TVG) is not only safer, but also more effective in sound insulation and heat insulation. In this paper, for the sound insulation performance of tempered vacuum glass, the acoustic wave transfer model of TVG is established, and the equation for sound insulation is deduced by using wave transfer method (WTM). Then the actual sound insulation loss of tempered vacuum glass was tested based on the method of reverberation room and anechoic room. finally, the sound insulation loss of tempered vacuum glass under different factors is analyzed. The results show that the theoretical calculation results are consistent with the experimental results about the general change trend of the sound insulation. The thicker the glass, the better the sound insulation. The more the supports in vacuum layer of tempered vacuum glass, the smaller the sound insulation loss. The thickness of the vacuum layer has different sound insulation loss at different frequencies. When the thickness of the vacuum layer is about 0.25 mm, tempered vacuum glass has the best sound insulation performance. This research will have important guiding significance for the selection of building sound insulation glass and the design of sound insulation glass.

The damage to coal-rock masses induced by mining disturbance cannot be overlooked, and the damage deformation characteristics under dynamic loading urgently require investigation. Therefore, this study employs Split Hopkinson Pressure Bar (SHPB) impact tests to reveal the energy evolution mechanism and fractal characteristics of coal failure under dynamic loading. Research indicates that coal deformation exhibits significant strain rate dependence, with both dynamic strength and energy consumption parameters increasing linearly with strain rate. Energy evolution drives crack development through four stages: no damage, microcrack initiation, macroscopic nucleation, and collapse, where the energy consumption required for crack formation exceeds that for crack propagation throughout the entire development process. The fractal dimension of fragmented coal satisfies a positive correlation with both strain rate and fragmentation energy density. Coal possesses favorable self-similarity, and under this condition, increased strain rate enhances the coal's ability to resist impact through elevated elastic energy density, thereby further strengthening dynamic strength. This confirms intensified fragmentation degree and refined fragment particle size under high energy consumption conditions, providing theoretical support for the prevention and control of mine dynamic disasters.

To study the effect of high temperature on the mechanical properties of red sandstone, YNS600 electro-hydraulic servo universal testing machine and pneumatic separating Hopkinson press bar (SHPB) device were respectively used to conduct static and dynamic load loading tests on red sandstone after 500~1000 ℃ action, and X diffraction detection. The damage pattern and mechanical property index changes before and after high temperature action were compared, and the relationship between mineral composition, microstructure and mechanical parameters of the specimens and temperature was analyzed, and a theoretical model was constructed. With the increase of temperature, the peak strength and elastic modulus under static and dynamic loading decreased significantly, and compared with the static stress-strain curve, the dynamic stress-strain curve did not have an obvious compaction phase, and the mass loss rate, volume expansion rate, and longitudinal wave velocity attenuation rate increased above 600 ℃. Minerals such as zeolite and pyrite within the red sandstone specimen gradually reacted after high temperature. The theoretical model explains the degradation mechanism of the mechanical properties of red sandstone under the action of idealized high temperature. The research results can provide a reliable scientific basis for the assessment and prediction of rock engineering after high-temperature fire.

To better understand the effects of protective coatings on concrete under fire conditions, various coatings were applied to different sections of concrete columns for high-temperature simulation tests. The performance of these coatings at elevated temperatures and the extent of concrete damage were assessed to identify more effective protective measures. This study conducted experiments to obtain real-time high-temperature stress-strain curves, temperature rise curves, and the compressive strength of coated concrete. Additionally, particle flow codes were used to develop models that captured the macroscopic and microstructural characteristics of both coatings and concrete. The software simulated two fire exposure modes: one-sided and four-sided heating. Coatings effectively preserved concrete, with tunnel fireproofing coatings (SD) demonstrating superior performance compared to gypsum-based plaster coatings (SG) and composite silicate protective coatings. At 800 degrees C, the compressive strength of SD reached 12.01 MPa, exceeding that of SG, GSY, and uncoated concrete (NC) by 8.39 %, 3.45 %, and 44.35 %, respectively. Under four-sided heating, the NC group exhibited reduced stress differentials due to its inability to bear the applied load at high temperatures, preventing effective load transfer. In contrast, onesided heating, though generating less heat, caused the NC group to tilt toward the heated surface, compromising overall structural stability. Coatings mitigated this effect, with SD effectively protecting the bottom part of column. Preventing the occurrence of one-sided flames is crucial to enhancing fire resistance. This study advances the understanding of how coatings protect concrete in fire conditions and proposes more effective measures to safeguard concrete columns and improve building safety.

With the deep extension of coal mining in China, fault water inrush has become one of the major disasters threatening the safety production of coal mine. Based on the control equations of steady state and non-Darcy seepage in fractured rock mass, the multi-parameter nonlinear dynamic seepage equations of fractured rock mass are established in this paper. Based on the nonlinear dynamics theory, the function of the state variable in the system is derived, and the influence of the gradual change of non-Darcy flow factors on the structural stability of seepage system is studied. The research achievements show that there are three branches in the equilibrium state of the seepage system. Specifically, the stability of the equilibrium state changes abruptly near the limit parameter. The seepage dynamic system of fractured rock mass has the delayed bifurcation, and the coal mine disaster such as fault water inrush occurs easily at the bifurcation point. The research results are of great significance to enrich the theory of fault water inrush in coal mine, and to reveal the disastrous mechanism of fault water inrush and guide its prevention and control technology in coal mine, which can provide the theoretical reference for predicting the water seepage stability in fractured rock mass.

In order to investigate the damage characteristics and evolution of the coal body under uniaxial impact loading,a Split Hopkinson Pressure Bar(SHPB)device was used to obtain the kinetic response of the coal sample at an impact velocity of 5 m/s by adjusting the air pressure value of the storage chamber,and this was used as the main reference to determine the fine physical and mechanical parameter of the model.Using PFC3D software,numerical simulations of the damage process of coal bodies containing closed and unclosed straight fissures at different angles(0°,30°,60°,90°)under uniaxial impact loading at 5 m/s impact velocity,and coal bodies without fissures at different impact velocity conditions were carried out.The influence of factors such as impact ve-locity and fracture distribution angle on the damage characteristics of coal bodies under uniaxial impact loading was investigated.The test results show that:when the impact velocity is low,the coal sample mainly follows the deformation damage criterion,and when the impact velocity increases to a certain degree,it mainly follows the strength damage criterion;fissures are usually generated by the four corners and the tip of the fissure and other media mutations,showing a"V"or"X"shaped trend of expansion,eventu-ally showing an X-shaped damage zone;the inner and outer layers of coal samples show different failure forms,the inner layer is closer to the triaxial stress state than the outer layer,so shear failure is more likely to occur,while the outer layer is more likely to oc-cur tensile failure.Overall,under uniaxial impact loading,the main form of damage to coal samples is tensile damage.

The air jet nozzle structure has a significant impact on the heat transfer uniformity and cooling rate of glass during the glass tempering process, and there is a lack of research on the discrepancy of different jet structures. The effects of double air knife, single air knife structures, and air hole structures on the cooling performance of glass in air-cooled tempering were investigated using numerical simulation and simplified analytical models. The calculated results are in agreement with the experimental results. The results show that the DK structure has a significant effect on improving the overall heat exchange performance of the glass, with lower surface temperatures for the same quenching time. The temperature inhomogeneities of DK, SK, and AH structures in the glass axial direction were 2.09%, 2.53%, and 3.33%, respectively, and the heat transfer uniformity of the DK structure was significantly better than the latter two. In comparison to the AH structure, the average heat transfer coefficients of the DK and SK structures increased by approximately 17.82% and 8.13%, respectively, while the heat transfer rates increased by approximately 7.05% and 4.51%. The study further improves the insufficiency of glass tempering research and provides theoretical guidance for the actual production of tempered glass.

The hidden collapse column has the characteristics of concealment, suddenness and connection with karst water, which pose a serious threat to safe production in coal mines. In this study, a numerical model of collapse columns with a random distribution of pores was constructed by a finite difference calculation program. Numerical simulation analyses of the coal mining face advance were carried out to explore the response characteristics of rock in the collapse column area under the influence of four factors: mining impact, lateral pressure coefficient, pore water and confined groundwater. The results show that the abutment pressure reaches its maximum when the working face advances to the boundary of the elastic stress elevated zone of the collapse column. The plastic zone above the collapse column shows a "Λ" shape and keeps growing during the advance of the working face. The height of the plastic zone in the top and bottom of the coal seam increases with the increasing lateral pressure coefficient. An increase in the lateral pressure coefficient can amplify the effect of mining on the vertical displacement and plastic zone distribution of the collapse column. When the collapse column is connected to the confined groundwater, the pore water pressure will increase significantly with the advancement of the working face. Under the joint action of confined groundwater and pore water, the extent of the plastic zone around the collapse column will be larger, and the development of the plastic zone inside the collapse column is especially obvious. This study will provide a basis for revealing the rock response rules in the area of the hidden collapse column during mining.