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This is an article in the field of mineral processing engineering. Copper is an important non-ferrous metal resource. With the increasing reduction of easily processed copper sulfide, the development and utilization of copper oxide is an important content of research in the mining field. Flotation is the main method to treat copper oxide. This paper summarizes the relevant research progress of copper oxide flotation in recent years, details the development status of direct flotation, sulfide flotation and other flotation methods, analyzes the flotation reagents, and discusses the future development direction of copper oxide flotation, aiming to provide an important theoretical basis for efficient separation of copper oxide.

This is an essay in the field of mineral processing engineering. Lead-zinc mine is one of the important strategic mineral resources in our country, and it is generally poor, fine and complex. Lead-zinc sulfide deposit is about 90% of total reserves. At present, flotation is the most commonly used method for the beneficiation of lead-zinc sulfide ore, and the selection of flotation reagents plays a decisive role in the flotation process index. In this paper, recent research progress of zinc sulfide flotation reagents is summarized, emphatically introduces the collecting agent, inhibitor and activator, analyzes the future the key research direction of zinc sulfide flotation, finally points out that the microbe as flotation reagents zinc sulfide flotation in the broad application prospect in the future, to achieve efficient vulcanization lead-zinc separation to provide technical and theoretical support.

Abstract Laboratory tests are one of the most fundamental and crucial methods in rock mechanics and engineering research. Natural rock specimens are challenging to acquire, and traditional casting methods involve prolonged curing times and cannot produce rock-like specimens with complex internal fractures. Furthermore, 3D printing technologies such as SLA, SLS, and FDM possess inherent limitations. In this study, high-silica sand was used as the printing material, and sand powder 3D printing technology was harnessed to fabricate rock-like specimens. Uniaxial compression tests were performed on specimens with varying placement times, aimed at investigating the impact of placement time on the mechanical properties of sand 3D-printed rock-like specimens. Acoustic emission technology was used to explore the internal state changes during deformation and failure of specimens with different placement times. The findings indicate that the mechanical properties of sand powder 3DP rock-like specimens exhibited no deterioration over time after approximately 7 days of placement. The internal structure remained unchanged across different placement times. This study's outcomes underscore the superiority of sand powder 3D printing technology within the realm of rock mechanics and establish the groundwork for the accurate and efficient fabrication of rock-like specimens through sand powder 3D printing technology in the future.

The weak rock mechanics is the basis of the control of coal mine roadway surrounding rock, which is generally of low strength and fractured. Due to the special characteristics of weak rocks in mechanics and structure, etc., there are problems in physical experiments such as the difficulty of specimens to meet the characteristics of fractures in the field and the strong discrete nature, which seriously restrict the research of weak rock mechanics or fractured rock mechanics tests. 3D printing technology is widely used in rock mechanics test research because of its technical advantages such as digital modeling and high accuracy, which breaks through the limitation of casting method in making complex specimens with fractures, but the specimens printed and formed by this technology are influenced by the printing materials and parameters which needs to be studied in depth. Based on sand powder 3D printing technology, this paper investigates the behavior and mechanisms of the effects of different types of sand powders and different binder saturation on the mechanical properties of weak rock-like specimens by means of mechanical tests, acoustic emission monitoring and electron microscopy scanning. The results show that different types of sand powders have significant effects on the mechanical properties and damage modes of the formed specimens due to their particle shape, size, and arrangement; the binder saturation has a positive correlation with the strength of the specimens, and changing the binder saturation can increase the strength of the specimens by 5 times under the same sand powder type, while the acoustic emission event signal and energy also increase with the increase of binder saturation. The results help to reveal the applicability and optimization basis of sand powder 3D printing technology for physical simulation of weak rocks, and provide an important basis for accurate and scientific reduction of mechanical properties of weak rocks in specific engineering conditions.

Abstract Soft rocks, such as coal, are affected by sedimentary effects, and the surrounding rock mass of underground coal mines is generally soft and rich in joints and cracks. A clear and deep understanding of the relationship between crack geometric parameters and rock mechanics properties in cracked rock is greatly important to the design of engineering rock mass structures. In this study, computed tomography (CT) scanning was used to extract the internal crack network of coal specimens. Based on the crack size and dominant crack number, the parameters of crack area, volume, length, width, and angle were statistically analyzed by different sampling thresholds. In addition, the Pearson correlation coefficients between the crack parameters and uniaxial compression rock mechanics properties (uniaxial compressive strength UCS, elasticity modulus E) were calculated to quantitatively analyze the impact of each parameter. Furthermore, a method based on Pearson coefficients was used to grade the correlation between crack geometric parameters and rock mechanical properties to determine threshold values. The results indicated that the UCS and E of the specimens changed with the varied internal crack structures of the specimens, the crack parameters of area, volume, length and width all showed negative correlations with UCS and E, and the dominant crack played an important role both in weakening strength and stiffness. The crack parameters of the angle are all positively correlated with the UCS and E. More crack statistics can significantly improve the correlation between the parameters of the crack angle and the rock mechanics properties, and the statistics of the geometric parameters of at least 16 cracks or the area larger than 5 mm2 are suggested for the analysis of complex cracked rock masses or physical reproduction using 3D printing. The results are validated and further analyzed with triaxial tests. The findings of this study have important reference value for future research regarding the accurate and efficient selection of a few cracks with a significant influence on the rock mechanical properties of surrounding rock mass structures in coal engineering.

Abstract This study aims to investigate the beneficial effects of surface retaining elements (SREs) on the mechanical behaviors of bolted rock and roadway stability. 3D printing (3DP) technology is utilized to create rock analogue prismatic specimens for conducting this investigation. Uniaxial compression tests with acoustic emission (AE) and digital image correlation techniques have been conducted on 3DP specimens bolted with different SREs. The results demonstrate that the strength and modulus of elasticity of the bolted specimens show a positive correlation with the area of the SRE; the AE characteristics of the bolted specimens are higher than those of the unbolted specimen, but they decrease with an increase in SRE area, thus further improving the integrity of the bolted specimens. The reinforcement effect of SREs on the surrounding rock of roadways is further analyzed using numerical modelling and field test. The results provide a better understanding of the role of SREs in rock bolting and the optimization of rock bolting design. Furthermore, they verify the feasibility of 3DP for rock analogues in rock mechanics tests.

Abstract The rock mass around deep roadways has obvious creep characteristics in high-stress environments. Meanwhile, the cyclic impact load induced by roof fracturing also causes dynamic damage to the surrounding rock, leading to long-term large deformation. This paper examined the rock mass deformation mechanism around deep roadways based on the theory of rock creep perturbation effect considering perturbation sensitive zone. This study proposed a long-term stability control guideline for deep roadways under dynamic load. An innovative support system was developed for deep roadways, with concrete-filled steel tubular support being recommended as the main supporting body. A case study was conducted to validate the proposed supporting system. Monitoring over one year in the case study mine showed that the overall convergence deformation of the roadway was 35 mm, indicating that the roadway’s long-term large deformation induced by creep perturbation was effectively controlled by using the proposed bearing circle support system.

Abstract The existence of joints or other kinds of discontinuities has a dramatic effect on the stability of rock excavations and engineering. As a result, a great challenge in rock mass mechanics testing is to prepare rock or rock-like samples with defects. In recent years, 3D printing technology has become a promising tool in the field of rock mass mechanics and engineering. This study first reviews and discusses the research status of traditional test methods in rock mass mechanics tests of making rock samples with defects. Then, based on the comprehensive analysis of previous research, the application of 3D printing technology in rock mass mechanics is expounded from the following three aspects. The first is the printing material. Although there are many materials for 3D printing, it has been found that 3D printing materials that can be used for rock mass mechanics research are very limited. After research, we summarize and evaluate printing material that can be used for rock mass mechanics studies. The second is the printing methodology, which mainly introduces the current application forms of 3D printing technology in rock mass mechanics. This includes printed precise casting molds and one-time printed samples. The last one is the printing model, which includes small-scale samples for mechanical tests and large-scale physical models. Then, the benefits and drawbacks of using 3D printing samples in mechanical tests and the validity of their simulation of real rock are discussed. Compared with traditional rock samples collected in nature or synthetic rock-like samples, the samples made by 3D printing technology have unique advantages, such as higher test repeatability, visualization of rock internal structure and stress distribution. There is thus great potential for the use of 3D printing in the field of rock mass mechanics. However, 3D printing materials also have shortcomings, such as insufficient material strength and accuracy at this stage. Finally, the application prospect of 3D printing technology in rock mass mechanics research is proposed.

Abstract Induced seismicity is strongly related to various engineering projects that cause anthropogenic in-situ stress change at a great depth. Hence, there is a need to estimate and mitigate the associated risks. In the past, various simulation methods have been developed and applied to induced seismicity analysis, but there is still a fundamental difference between simulation results and field observations in terms of the spatial distribution of seismic events and its frequency. The present study aims to develop a method to simulate spatially distributed on-fault seismicity whilst reproducing a complex stress state in the fault zone. Hence, an equivalent continuum model is constructed, based on a discrete fracture network within a fault damage zone, by employing the crack tensor theory. A fault core is simulated at the center of the model as a discontinuous plane. Using the model, a heterogeneous stress state with stress anomalies in the fault zone is first simulated by applying tractions on the model outer boundaries. Subsequently, the effective normal stress on the fault plane is decreased in a stepwise manner to induce slip. The simulation result is validated in terms of the b-value and other seismic source parameters, hence demonstrating that the model can reproduce spatially and temporally distributed on-fault seismicity. Further analysis on the parameters shows the variation of frequency-magnitude distribution before the occurrence of large seismic events. This variation is found to be consistent with field observations, thus suggesting the potential use of this simulation method in evaluating the risk for seismic hazards in various engineering projects.

In this study, GX2 was applied as a new high-efficiency chalcopyrite depressant to selectively separate molybdenite from Cu-Mo sulfide ores. The flotation performance and its interaction mechanisms with chalcopyrite and molybdenite were investigated using single-mineral and artificial-mixed-ore flotation, contact angle measurements, zeta-potential measurements, infrared spectroscopy, and X-ray optoelectronic spectrum analysis. The results indicated that molybdenite could be selectively separated from chalcopyrite under the optimal flotation conditions of pH 9.0, 80 mg/L GX2, 20 mg/L kerosene, 10 mg/L MIBC, and a flotation time of 3 min, while the molybdenite and chalcopyrite recoveries were around 90% and 5%, respectively. It was confirmed that GX2 could save ten times the depressant dosage compared to that of the Na2S baseline to achieve a similar separation efficiency. The contact angle test, zeta potential, infrared spectrum, and XPS results show that GX2 may be adsorbed on the surface of chalcopyrite via chemical adsorption, and the hydrophilic substances formed change its hydrophobicity, whereas the effect on the floatability of molybdenite is small, resulting in the excellent separation efficiency of chalcopyrite and molybdenite via flotation.

In this study, chemical leaching, XRD, SEM, and XPS analyses were conducted to investigate the dissolution and passivation mechanisms of chalcopyrite under pressurized oxidative conditions in water. The chemical leaching results showed that the chalcopyrite could be dissolved by pressurized leaching without any acid addition, i.e., in an O2–H2O system, and the copper leaching rate reached 96.4% under the optimal conditions of 180 °C, 1.5 MPa, 900 rpm, and 90 min. The XRD, SEM, and XPS data suggested that a large proportion of the chalcopyrite dissolved in solution via the mineral phase transformation of CuFeS2→Cu2+ and CuFeS2→CuS→Cu2+, i.e., some of the chalcopyrite directly leached into solution as Cu2+, and some of it was first converted to CuS and then to Cu2+. The primary passivation layers during the chalcopyrite pressurized water leaching were hematite, pyrite, and covellite; however, none of them covered the un-leached mineral surface or inhibited chalcopyrite dissolution, as long as the agitation speed and leaching time were maintained over 700 rpm and 60 min, respectively. Finally, a model of chalcopyrite’s dissolution and passivation mechanism during pressurized water leaching was proposed.

AbstractThe presence of joints and other types of discontinuities has a significant effect on the mechanical properties of rock, especially for tensile properties to fundamentally influence the stability of rock excavations. The main challenge associated with the experimental research on jointed rock lies in the difficulty to carry out amount of direct tensile tests for analysis of the effect of joint geometric parameters on mechanical properties. In this study, a particle flow model was established by utilizing the flat-joint contact model (FJM) to represent the rock materials. After microscopic parameter calibration, 53 sets of the numerical model were used for investigating the relationship between jointed geometric parameters and tensile mechanical properties. The results show that the crack initiation is related to trace length l and joint angle β, and the tensile-shear crack will appear as β increase. The uniaxial tension strength σt and β had first a weak negative correlation and then a positive correlation as the β increases, which was consistent with mathematical calculations. Furthermore, the relative importance (RI) analysis showed that the β plays a decisive role among the joint geometric parameters for affecting σt, and the effect factors of σt were joint angle β, length l, density n, and aperture d in that order. The present research can be utilized for multiple purposes in the field of jointed rock engineering, such as prediction of surrounding rock instability analysis and estimating the variable values in the inversion analysis in practical engineering projects.

AbstractThe stability of the entries of longwall panels is the key to ensure efficient and safe production of coal mines. In order to solve the common problems of floor heave of panel entry in western China, based on a case study, this paper studies the rockburst instability mechanism of entry floor-induced mining by considering the results from a laboratory test, numerical simulations, and field practice. After testing, the coal and rock of the entry are hard and brittle. In particular under the action of impact dynamic load, its dynamic strength is higher and has a positive correlation with the impact pressure, which provides a mechanical premise for subsequent rockburst. Numerical simulation results show that with the mining of the panel, the vertical stress and the maximum principal stress of the floor are mainly concentrated in the coal pillar along the entry, and the area and degree of concentration continue to increase. The horizontal stress is mainly concentrated in the entry floor, which is distributed in the advanced range of the panel. The deformation rate of the entry roof and the ribs is stable, while the floor shows a “mutation” characteristic of not deforming when the panel is far away and suddenly rising when it is closer to the panel. The range of the plastic zone of the roof and floor remains unchanged, the ribs are further deepened, and the mechanical properties of the coal and rock mass are further weakened. The results of this study contribute to providing a reference for the control of surrounding rock of panel entry under similar geological and geotechnical circumstances.

AbstractIn order to understand the mechanism of some unconventional failures such as rockburst caused by deep rock excavation, the failure characteristics of burst-prone sandstone specimens under static and dynamic loads were studied by using the MTS816 rock mechanics testing system and the split Hopkinson pressure bar (SHPB) experimental system, as well as the effects of bedding angle and impact pressure on rock mechanical properties and failure patterns. The uniaxial compression test used a cylindrical specimen with a height of 50 mm and a diameter of 100 mm, and cylindrical specimens with height and diameter of 50 mm were adopted in the SHPB tests. The bedding angles in the tests are 0°, 45°, and 90°. In the dynamic impact test, three different impact pressures were applied to observe the magnitude of impact load on the mechanical behaviors of the burst-prone sandstone specimens. The results show that with the increase in the bedding angle, the uniaxial compressive strength firstly decreases and then increases. When the bedding angle is 45°, the uniaxial compressive strength is the lowest. The uniaxial compressive strength is highest when the bedding angle is 0°. The burst-prone sandstone specimens with different bedding angles had three different failure pattern types. Under the dynamic loading, the stress-strain curves show springback phenomenon; with the increase in impact pressure, the dynamic strength of the burst-prone sandstone specimens with each bedding angle increases; the fracture degree of the bedding sandstone specimens gradually increases. The dynamic strength of the 45° burst-prone sandstone specimen is the lowest, and it has the highest fracture degree.

The application of sand powder three-dimensional (3D) printing technology in the field of rock mechanics and mining engineering has tremendous potential, but it is still in the preliminary exploration stage. This study investigated the effect of printing layer thickness on the physical and mechanical properties of rock-like specimens with sand powder 3D printing. Quartz sand powder was used as the printing material, and the specimens were prepared with three different layer thicknesses of 0.2, 0.3, and 0.4 mm. Uniaxial compression tests with a combination of digital image correlation (DIC), acoustic emission (AE) and 3D microscope observations were performed to analyze the mechanical properties and failure patterns of the specimens during loading. Experimental findings showed that increasing the layer thickness from 0.2 to 0.4 mm would result in a decrease in the weight, density, uniaxial compression strength, and elastic modulus of the specimens. The stress-strain curve, deformation and failure patterns, crack growth process, and AE characteristics of the specimens with a layer thickness of 0.2 mm are similar to the AE characteristics of rock-like material, whereas the specimens with layer thicknesses of 0.3 and 0.4 mm deform like a ductile material, which is not appropriate for simulation of coal or rock mass. In future studies, rock-like specimens should be prepared with a small layer thickness.

In order to explore the deformation and failure evolution characteristics of the surrounding rock during the connection process of the deep rock burst drivage roadway under the dynamic load disturbance, and based on this, the catastrophe mechanism of the roadway is analyzed, taking the rock burst accident of Longyun Coal Industry in Shandong Province on October 20, 2018, as the engineering background. FLAC3D was used to study the distribution evolution law of displacement, plastic zone, and stress field in the whole process of “Roadway Drivage-Deformation and Failure-Instability and Disaster” in the surrounding rock of deep roadway. The research results show that under the conditions of high stress and dynamic load disturbance, the surrounding rock deformation and failure are significant during the connection of the thick-top-coal roadway in deep, the roof is the most, the two ribs are the second, and the roadway top-coal is in an “inverted trapezoid” sag pattern. When the length of the bolts is limited or the anchoring force of the cables is not enough to effectively restrain the roof, the impact of dynamic disturbance on the plastic damage of the roof is greater than that of the two ribs and the floor, and the plastic damage of the coal seam roof affecting the surrounding rock deformation of the roadway drivage played a leading role.

There are various complex joints (fissures), laminae, and other soft structural surfaces in the roadway enclosure, and the existence of these soft structural surfaces seriously affects the stability of the roadway enclosure. In order to study the mechanical properties of the coal body and the development of joints during coal fracture, this paper establishes a three-dimensional model of the fracture structure of the coal body based on CT scanning and three-dimensional reconstruction technology. On this basis, a 3D numerical model of the equivalent nodal coal body is constructed, uniaxial compression simulation analysis is performed, and the joint evolution development law of the coal sample is studied by the built-in joint monitoring program of PFC3D. The results show that the larger the effective joint area and larger the joint size inside the coal sample, the smaller the compressive strength of the coal sample. The increase of joint size and joint surface area increased the ductility and stress-strain curve multipeak phenomenon of the coal sample to some extent. During the rupture of the coal sample, the changes of each phase of the statistical curve of joint number and the phases of the stress-strain curve of the coal sample are compatible.

With the increasing depth of coal mining and expanding mining scale, the rocks surrounding deep roadways are in a complex mechanical condition of frequent dynamic disturbance. The heterogeneity has an important influence on rock mass failure under dynamic loads. Therefore, it is necessary to study the deformation and failure of heterogeneous roadway under dynamic load. In this paper, the effect of heterogeneity on stability of roadway under static and different dynamic loads is studied. According to the results, the effect of rock mass heterogeneity on the deformation and failure of surrounding rock varies with different degrees of heterogeneity. Under static loading conditions, the stability of roadway is negatively correlated with the degree of heterogeneity of the rock mass. Under dynamic loading conditions, the change of heterogeneity degree has significant influence on the stability of surrounding rock. With the increase in dynamic load strength, the change in variation difference in the average value of roof sag, stress distribution, and plastic zone caused by variations in heterogeneity will increase. This study contributes to understanding the deformation and failure characteristics of heterogeneous roadways under dynamic loads and can be used to analyze heterogeneous roadways under dynamic loads.

Dynamic and static coupling loads (DSLs) are one of the most common stress environments in underground engineering. As the depth of a roadway increases over the life of a mine, the static load of the ground stress field increase multiplies, and the cyclic operation at the working face releases a large amount of dynamic energy. Therefore, deep roadways easily induce dynamic disasters during production. In this paper, a deep roadway numerical model was built with FLAC3D to test the deep roadway under DSLs and was simulated with 16 different support designs. The ground stability in each support condition was examined and compared in terms of the ground deformation and scope of failure. The underlying support mechanism was further analyzed with numerical modeling in view of the deformation in the surrounding rock mass induced by variations in the support parameters. The results show that shortening the bolt spacing is an effective measure to control the deformation of surrounding rock whatever DSLs or static load. Under static load, the larger the anchoring length is, the more stable the surrounding rock is. Under DSLs, end grouting length (S = 600 mm) and full grouting length (S = 1800 mm) can effectively control the deformation of surrounding rocks and enhance the stability of surrounding rocks. The results contribute to the design of supports in the field of underground coal mines and provide a basis for determining the reasonable support scheme for roadways.

In the field of rock engineering, tensile failure is one of the most significant failure modes due to the presence of joints/fractures. However, due to the limitations of current laboratory testing, it is difficult to carry out direct tensile tests on jointed rock specimens in the laboratory. To study the effect of joints on the mechanical behavior and failure mode of jointed rock specimens, a three-point modeling method that can consider arbitrarily arranged rock joints is deduced and applied to discrete element simulation. The effects of different joint angles (the inclination angle α, rotation angle β, and superimposed angle γ of α and β, where γ is the angle between the joint and horizontal plane), the density (n), and the rate of cutting area (RCA) of the specimen loading surface (LSS) on the tensile strength (σt), elastic modulus in tension (Et), and failure mode of the specimens were analyzed. The results show that the joint angle (considering α, β, and γ) and RCA have a significant effect on the resulting σt and failure mode, while n has a significant effect on Et. The failure mode of the specimen changes from tensile failure along the joint to direct tensile failure of the specimen as γ increases, and the mechanical behavior transitions from unstable to stable. In addition, the main influence of γ on the mechanical behavior of specimens is revealed, and the change process of the failure mode after the cutting of the LSS is analyzed. The present research can be utilized for multiple purposes, including the joint development of surrounding rock and failure dominated by tensile failure in underground engineering, especially for tunnels, roadways, chambers, and so forth.

To study the correlation among advancing direction, strata behaviors, and rock burst induction, two physical models utilizing similar materials are established. Subsequently, the influence of advancing direction on the mining effect, caused by a fault, is studied. Moreover, the rock bursts affected by faults with different mining directions are compared and analyzed. The results show that the overlying structure varies notably, affected by fault cutting and fault dip, and the fault-affected zone and the cause of induced rock burst differ with different mining directions. However, regardless of mining directions, the overlying structure of the hanging wall is stable and fault activation is not obvious, while that of the footwall is relatively active and fault activation is violent; the risk of rock burst on the footwall is larger than that of mining on the hanging wall. Finally, an engineering case regarding two rock bursts in panel 6303 is used to verify some physical simulation results to a certain extent. Study results can serve as a reference for face layout and prevention of rock bursts under similar conditions.

In a catalytic combustion of ventilation air methane, one of the key factors determining the reactor performance is the geometry of the reactor. It should be designed to provide maximum energy conversion at minimum catalyst usage and operating cost. This numerical study is conducted to investigate the catalytic combustion of ventilation air methane from a gassy underground mine in a circular straight and helical reactor channel with twisted tape insert. A three-dimensional computational fluid dynamics model which considers conservation of mass, momentum, energy, and species together with chemical reactions, and constitutive relations for species properties and reactions kinetics was developed and validated against the previously published data. The effect of several key factors affecting the catalytic combustion performance such as inlet Reynolds number, twisted tape ratio, and reactor length are evaluated to obtain the optimum reactor parameters. For evaluation purpose, the reaction performance of the studied reactors will be compared to the straight reactor without twisted tape which is set as a baseline. The results give a firm confirmation on the superior performance of the reactors with twisted tape insert as compared to those without. In addition, it is found that helical reactors generate higher net power as compared to their respective straight reactor counterpart despite having lower FoM due to larger catalyst area. Interestingly, the higher twisting ratio offers better performance in terms of net power as well as FoM. Overall, the results highlight the potential of twisted tape insert application in catalytic combustion.

Uniaxial compressive strength (UCS) and peak strain (PS) are essential indices for studying the mechanical properties of coal and rock masses, and they are closely related to mechanical parameters such as the elastic modulus (E), Poisson’s ratio (υ), cohesion (C) and internal friction angle (Φ) of coal and rock masses. This study took the No. 2-1 coal seam of Zhaogu No. 2 Mine, in Henan Province, China, as the research object. An RMT-150B servo testing machine was used to test all mechanical parameters, including the E, υ, C and Φ of coal and rock masses. Based on the principle of orthogonal testing, Three Dimensions Fast Lagrangian Analysis of Continua (FLAC3D) was used to select E, υ, C, Φ, tensile strength (Rm) and dilation angle (Ψ) as initial participation factors. Using these six parameters and a five-level combination scheme (L25 (56)), the influence of coal mechanical parameters on UCS and PS was investigated, using the software SPSS for stepwise regression analysis, and a uniaxial pressure-resistant regression prediction equation was established. The research showed that, under uniaxial compression conditions, the main parameters controlling UCS of coal masses are C and Φ; conversely, the main parameters controlling PS are E and C. UCS and PS exhibit significant linear relationships with these main controlling parameters. Here, a stepwise regression prediction equation was established through reliability verification analysis using the main controlling parameters. This prediction method produces very small errors and a good degree of fit, thus allowing the rapid prediction of UCS. The precision of the stepwise regression model depends on the number of test samples, which can be increased in the later stages of a design project to further improve the precision of the projection model.

Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation and rock-burst potential of roadways under different dynamic and static loads. The results show that the larger the dynamic load is, the greater the increase in the deformation of the roadway under the same static loading conditions. A roadway under a high static load is more susceptible to deformation and instability when affected by dynamic loads. Under different static loading conditions, the dynamic responses of the roadway abutment stress distribution are different. When the roadway is shallow buried and the dynamic load is small, the stress and elastic energy density of the coal body in the area of the peak abutment stress after the dynamic load are greater than the static calculations. The dynamic load provides energy storage for the coal body in the area of the peak abutment stress. When the roadway is deep, a small dynamic load can still cause the stress in the coal body and the elastic energy density to decrease in the area of the peak abutment stress, and a rock-burst is more likely to occur in a deep mine roadway with a combination of a high static load and a weak dynamic load. When the dynamic load is large, the peak abutment stress decreases greatly after the dynamic loading, and under the same dynamic loading conditions, the greater the depth the roadway is, the greater the elastic energy released by the dynamic load. Control measures are discussed for different dynamic and static load sources of rock-burst accidents. The results provide a reference for the control of rock-burst disasters under dynamic loads.

The membrane electrode assembly (MEA) plays an important role in the proton exchange membrane fuel cell (PEMFC) performance. Typically, the structure comprises of a polymer electrolyte membrane sandwiched by agglomerate catalyst layers at the anode and cathode. Optimization of various parameters in the design of MEA is, thus, essential for reducing cost and material usage, while improving cell performance. In this paper, optimization of MEA is performed using a validated two-phase PEMFC numerical model. Key MEA parameters affecting the performance of a single PEMFC are determined from sensitivity analysis and are optimized using the response surface method (RSM). The optimization is carried out at two different operating voltages. The results show that membrane thickness and membrane protonic conductivity coefficient are the most significant parameters influencing cell performance. Notably, at higher voltage (0.8 V per cell), the current density can be improved by up to 40% while, at a lower voltage (0.6 V per cell), the current density may be doubled. The results presented can be of importance for fuel cell engineers to improve the stack performance and expedite the commercialization.

It is well accepted that faults have significant impacts on the safe production of underground coal mines; however, the fault-slip mechanism during longwall mining through a fault still needs to be investigated. In this study, the distribution of microseismicity events during panel mining through a fault is analyzed, and 3-dimensional fast Lagrangian analysis of continua was used to study the mining stress distribution and fault-slip behavior under the two different mining directions, i.e., mining the panel through the fault from the footwall, or mining the panel through the fault from the hanging wall. The research shows that when the panel is mined through the fault from the footwall, the shear displacement of the fault is significantly greater than those created by mining the panel through the fault from the hanging wall. Under the two mining directions, the variation behaviors of the normal stress and shear stress on the fault are quite different, and fault-slips mainly occur in fault areas where the normal stress decreases. When mining the panel through the fault from the footwall, the slip mainly occurs in the coal-seam roof fault, and when mining the panel through the fault from the hanging wall, the slip mainly occurs in the coal-seam floor fault. According to the variations in the normal stress and shear stress of the fault during the period of mining the panel through the fault, the mechanism of the fault slip can be divided into three categories. 1: Normal stress and shear stress decrease abruptly, but the reduction of the normal stress is greater than that of the shear stress. 2: The normal stress is continuously reduced, the shear strength of the fault is decreased, and the shear stress is suddenly increased. 3: Both the normal stress and the shear stress increase, but the increase in the shear stress is greater than that of the normal stress. These research results can provide a reference for the layout of panels and for fault-slip-induced disaster prevention under similar conditions.

By employing the longwall mining method, a series of intensive strata structure responses and activities will be induced including stress redistribution, fracture extension and strata movement. Due to the geological stratification feature of coal mine strata, tensile failure and tension-induced fracturing play dominant roles in the strata of the fractured zone. These responses induced in the strata require the consideration of the weakening effect on the rock mass behavior due to failure and fracturing in tension. In this study, a numerical modeling approach on mining-induced strata structural behaviors was proposed by considering the mechanical behaviors of the caved zone consolidation and tension-induced weakening in the fractured zone. Based on a numerical model built according to a study site, a parametric study with respect to different fracturing intensity parameters was performed to investigate the fracturing weakening effect on the mining-induced stress redistribution and strata movement. The numerical results showed that the tensile fracture intensity had a notable effect on the mining-induced stress distribution in two aspects: (1) Increase in peak and area of the front abutment stress; (2) variation in the patterns of stress recovery in the goaf. The stress data obtained from numerical simulation represent and help to back-analyze the structural behaviors (failure, movement) of the overlying strata. The high stress on the coal seam indicated that the strata lay on and transferred loads to the seam, while the low stress indicated the detachment between the seam and the suspending strata. With the increase in fracture intensity, the roof strata were more prone to breaking and caving, and the suspending length of the roof beam decreased, which made the strata sufficiently break, cave and transfer the overburden load to loose rock in the goaf; caving along the strike direction of the panel became the dominant overlying strata structure movement, while the dominant movement caved along the dip direction in the case of strong and intact overlying strata with few tensile fractures. Thus, the tensile fracturing intensity should not be ignored in studies related to the behaviors of the overlying strata. Validated by analytical studies, this study presents a novel numerical modeling approach for this topic and can be utilized for multiple studies based on proper roof fracturing estimation or back analysis.

In a complex stress field of underground mining or geotechnical practice, tension damage/failure in rock masses is easily triggered and dominant. Unlike metals, rocks are generally bi-modularity materials with different mechanical properties (Young’s modulus, etc.) in compression and tension. It is well established that the Young’s modulus of a rock mass is directly related to the presence of the fracture or joint, and the Young’s modulus estimation for jointed rocks and rock masses is essential for stability analysis. In this paper, the tensile properties in joint rocks were investigated by using numerical simulations based on the discrete element method. Four influencing parameters relating to the tensile properties (joint dip angle, joint spacing, joint intersection angle, and joint density) were studied. The numerical results show that there is an approximately linear relationship between the joint dip angle (α) and the joint intersection angle (β) with the tensile strength (σt), however, the changes in α and β have less influence on the Young’s modulus in tension (Et). With respect to joint spacing, the simulations show that the effects of joint spacing on σt and Et are negligible. In relation to the joint density, the numerical results reveal that the joint intensity of rock mass has great effect on Et but insignificant effect on σt.

During active mining operation of a gassy underground mine, large amounts of methane will be released from the mine ventilation shaft. To eliminate the harmful effects of this ventilation air methane and minimize the wastage of this potential energy resource, considerable effort has been devoted to converting this alternative fuel using catalytic combustion. This study numerically investigated the reaction performance of ventilation air methane (VAM) in helical coil tubes of various configurations utilizing a computational fluid dynamics (CFDs) approach. Several key factors affecting the catalytic combustion performance such as curvature, inlet Reynolds number, and cross-section aspect ratio were evaluated. Recalling the high cost of the catalyst used in this reaction—platinum—optimization of catalyst usage by implementing selective catalyst coating was conducted and investigated. For evaluation purposes, the reaction performance of the helical coil tube was compared to its straight counterpart. The results gave a firm confirmation of the superior performance of the helical coil tube compared to the straight one. In addition, it was found that the selective inner wall coating in the circular cross-section at a higher Reynolds number gave rise to the highest figure of merit (FoM), defined as the net energy produced per mg of catalyst platinum.

Owing to its relatively high heat transfer performance and simple configurations, liquid cooling remains the preferred choice for electronic cooling and other applications. In this cooling approach, channel design plays an important role in dictating the cooling performance of the heat sink. Most cooling channel studies evaluate the performance in view of the first thermodynamics aspect. This study is conducted to investigate flow behaviour and heat transfer performance of an incompressible fluid in a cooling channel with oblique fins with regards to first law and second law of thermodynamics. The effect of oblique fin angle and inlet Reynolds number are investigated. In addition, the performance of the cooling channels for different heat fluxes is evaluated. The results indicate that the oblique fin channel with 20° angle yields the highest figure of merit, especially at higher Re (250⁻1000). The entropy generation is found to be lowest for an oblique fin channel with 90° angle, which is about twice than that of a conventional parallel channel. Increasing Re decreases the entropy generation, while increasing heat flux increases the entropy generation.