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Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter's realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock's mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions. [ABSTRACT FROM AUTHOR]

Aiming at the problem of large deformations and difficult maintenance of cross-mining floor roadways, taking the track transportation roadway of the cross-mining east wing floor in Qinan Coal Mine as the engineering background, the stress field distribution of mining stress in floor strata and surrounding rock of floor roadway during the cross-mining process of the working face is studied by combining theoretical analysis with numerical simulation. The results show that the influence of mining stress on the vertical stress of floor strata is reflected in the stress-increasing area in front of the coal wall and the stress-decreasing area in the rear of the coal wall. With the increase in the depth of the floor strata, the peak value of the vertical stress gradually decreases, and the distance from the peak value of the vertical stress to the coal wall and the influence range of the vertical stress gradually increases. When the width of the coal pillar is greater than the influence range of advance abutment pressure of the working face, the development speed of the plastic zone is slow. When the roadway is located in the influence range of advance abutment pressure, the plastic zone of the roadway's surrounding rock develops rapidly. When the working face crosses the floor roadway more than 10 m, the depth of the plastic zone of the surrounding rock of the roadway is no longer increased; the siltstone above the roadway is the key layer of fracturing, and the deformation of the roadway has been effectively improved after hydraulic fracturing. Through the analysis of numerical simulation results, the fracturing scheme has a significant effect on the stability control of the surrounding rock of the cross-mining floor roadway. This study has certain guiding significance for the maintenance and sustainable utilization of floor roadways in the cross-mining process, which is conducive to ensuring the sustainable mining of underground coal and the safety of personnel and equipment and is of great significance to the sustainable development of the coal mining industry. [ABSTRACT FROM AUTHOR]

To address the challenging issues of large deformation, control difficulties, and susceptibility to failure in the support structure of soft coal roadways, this study utilizes the CVISC block creep model in UDEC software. The model incorporates Coulomb slip without cohesive contact to simulate the characteristics of soft coal, such as its loose, fragile, and small-block nature. Additionally, a soft coal nonlinear discrete element creep model is developed to investigate the creep characteristics of soft coal under triaxial compression, with the aim of revealing the underlying creep destabilization mechanism in soft coal tunnels. Based on the research findings, a primary, strong active support technology is proposed. This approach involves the use of high-preload, high-strength anchor rods and anchor cables, as well as the implementation of steel mesh and plastic woven mesh to enhance surface protection. The study highlights that: (1) The shear cracks inside the coal body of the soft coal specimen transform into tensile cracks under external force, leading to an increase in the number of tensile cracks. This is an important symbol of accelerated creep in soft coal. Improvement in peripheral pressure helps inhibit the generation of tensile cracks inside the specimen. (2) The rapid development of creep and inter-particle tensile fissures within the coal body particles themselves, along with the change in stress state after the excavation of the roadway, are the main reasons for the overall creep damage of the roadway. (3) The support force in the early stage of shed cable support is small, which cannot inhibit the accelerated development of tensile fissures. This leads to continuous deformation of the roadway, resulting in the failure of the support structure in the later stage and aggravated roadway damage. (4) The new support technology helps control surface deformation by enhancing the strength of the roadway protection surface. This suppresses the development speed and number of tensile fissures during roadway deformation, improves the starting strength of the roadway for accelerated creep, and enables effective control of the overall deformation of the soft coal roadway. Thus, the effectiveness of roadway support is remarkable. [ABSTRACT FROM AUTHOR]

Previously conducted studies have established that the sudden collapse of large areas of overhanging roofs in longwall working faces can cause shock loads and wind blast. In order to solve the problem of the hard and stable roof (HSR) being difficult to collapse in the initial mining stage, a combination of theoretical analysis and numerical simulation is used, taking Dongqu coal mine as the engineering background. The mechanical model of the initial fracture of the main roof is established, the relationship between the thickness-to-span ratio of main roof, the internal stress of the roof is analyzed, and the relationship between the thickness of the roof and the initial weighting step is revealed. The method of hydraulic fracturing (HF) is proposed to pre-crack the main roof in order to achieve controllability of the roof. The effect of HF on the control of the HSR is analyzed. The main conclusions are as follows: under the condition of a certain span of the rock beam, a smaller thickness of the rock beam makes for a larger tensile stress inside of it, increasing the likelihood that the rock beam will fracture. It is possible to reduce the initial weighting interval of the main roof by decreasing the thickness of the HSR and increasing the thickness of the load layer. The abutment pressure in the initial mining stage is obviously reduced after HF. The technical scheme of HF was proposed and applied in the field, and the field observations show that after HF, the HSR can collapse in time at the initial mining stage, leading to remarkable results being achieved. [ABSTRACT FROM AUTHOR]

The mining confrontation caused by a super-long working face is an important factor that leads to difficulties in the control of surrounding rock in facing-mining roadways. To address this issue, this study takes the 18106 working face of Xiegou Coal Mine as the engineering background. First, deformation characteristics of the surrounding rock in two stages of roadway mining are explored, and the principle of determining the time for fracturing construction is presented. Additionally, the influence of fracturing space position on the control effect of the roadway's surrounding rock is examined. Results show that the roadway which is influenced by adjacent working face mining has obvious asymmetric deformation, and the order of deformation is as follows: pillar side > roof > coal side > floor. The roof activity in goaf is the key factor of roadway deformation, and the proportion of deformation is 60%, followed by the influence of advance stress, accounting for 38%. After fracturing, with the increase in fracturing height, the deformation of the surrounding rock decreases, and the decrease in deformation of the roof and two sides also reduces, while the decrease in deformation of the floor remains relatively stable. The reasonable fracturing height is 10 m, and the reasonable fracturing construction time is 17 days before the confrontation between the working face and the roadway. Field practice suggests that there are effective cracks in the roof after fracturing, and the deformation of the surrounding rock in facing-mining roadways is reduced by more than 60% compared to that without fracturing. Hydraulic fracturing is significant for controlling the deformation of the surrounding rock in facing-mining roadways. [ABSTRACT FROM AUTHOR]

Strong mine pressure has a great impact upon the safety production of coal mines. Microseismic information provides a more advanced technical means for overburden fracture dynamic identification and mine pressure mechanism research, since it contains rich information on rock fracture sources. In this study, the isolated LW8102 working face in Tongxin Mine was investigated in order to propose a spatio-temporal microseismic event data analysis method based on the k-means clustering algorithm. This algorithm can handle dynamic identification of overburden fractures constrained by spatiotemporally discrete distributions of microseismic events. This provided the dynamic extension process and the fracture distribution pattern of the overburden: eight fracture extensions were formed in the overburden. In each extension, vertical fractures connected the low and high rock layers in the LW8102 and LW8103 goafs, and through fractures connected the LW8102 and LW8103 goafs in their high, middle, and low levels. Some extensions had fractures that were connected to form a closed loop structure. In the vertical fracture, there was a tendency for one or two layers of the stratum to fail first, and then extend to one or both sides. The process of through and vertical fracture propagation followed a certain temporal sequence, reflected primarily in two forms: firstly, as the vertical fracture extended to a certain layer, it provided the initial rupture space for through fracture spreading; secondly, the through fracture first broke, and then extended to the vertical fracture until it intersected with the vertical fracture or provided the initial rupture space for the expansion of the vertical fracture. By matching the overburden fracture to the mine pressure that responded to the support resistance, we analyzed the mechanism of mine pressure at the working face. Through fracture at the high level was found to be the primary cause of the occurrence of mining pressure. It was precisely placed that the formation of multiple adjacent high through fractures 110 m from the floor, triggering simultaneous instability motion of the lower multi-layer level rock; this was the main reason for the phenomenon of strong mine pressure at the working face. Meanwhile, high through fracture at 80 m from the floor was the main reason for the phenomenon of large mine pressure at the working face. [ABSTRACT FROM AUTHOR]

The problem of asymmetric large deformation of surrounding rock of heading roadways is prominent due to the superposition of mining stress in the mining intersection area. Therefore, on the basis of the background of 18,106 tailentry in the Xiegou Coal Mine, this paper establishes a mechanical model of surrounding rock deformation of mining roadways under the effect of advanced abutment pressure. In the model, we deduce the theoretical calculation formula of roadway full-section deformation and discuss the influence factors of roadway surrounding rock deformation. Accordingly, the deformation mechanism of surrounding rock of mining roadways and the engineering suggestions and measures are revealed. The main results and finding are threefold. Firstly, the increase of the stress concentration factor of the coal pillar rib and the increase of the width of the failure zone are the fundamental reasons leading to the aggravation of the surrounding rock deformation on the side of the coal pillar in the heading roadway. Secondly, the deformation of the coal pillar rib increases with the increase of stress concentration factor and decreases with the increase of coal cohesion, internal friction angle, elastic modulus, and roadway rib support resistance. Additionally, the deformation of the roadway roof and floor decreases with the increase of roadway rib support resistance and is inversely proportional to the cubic power of rock beam thickness and elastic modulus. The deformation rate of the roadway roof and floor increases with the increase of vertical stress concentration factor of the coal pillar rib, and the maximum deformation position shifts to the side of the coal pillar. Therefore, increasing the strength and stiffness of the roadway surrounding rock and the supporting resistance of surrounding rock can reduce the deformation of roadway surrounding rock and the influence of advanced abutment pressure on roadway deformation. In the end, the rationality and feasibility of the theoretical analysis is verified through an engineering example. Under the influence of advanced abutment pressure, the deformation of roadway floor heave is the most severe, the asymmetrical deformation on both sides of the roadway is remarkable, and the deformation of coal pillar side is about twice that of solid coal side. [ABSTRACT FROM AUTHOR]

The timely detection of equipment failure can effectively avoid industrial safety accidents. The existing equipment fault diagnosis methods based on single-mode signal not only have low accuracy, but also have the inherent risk of being misled by signal noise. In this paper, we reveal the possibility of using multi-modal monitoring data to improve the accuracy of equipment fault prediction. The main challenge of multi-modal data fusion is how to effectively fuse multi-modal data to improve the accuracy of fault prediction. We propose a multi-modal learning framework for fusion of low-quality monitoring data and high-quality monitoring data. In essence, low-quality monitoring data are used as a compensation for high-quality monitoring data. Firstly, the low-quality monitoring data is optimized, and then the features are extracted. At the same time, the high-quality monitoring data is dealt with by a low complexity convolutional neural network. Moreover, the robustness of the multi-modal learning algorithm is guaranteed by adding noise to the high-quality monitoring data. Finally, different dimensional features are projected into a common space to obtain accurate fault sample classification. Experimental results and performance analysis confirm the superiority of the proposed algorithm. Compared with the traditional feature concatenation method, the prediction accuracy of the proposed multi-modal learning algorithm can be improved by up to 7.42%. [ABSTRACT FROM AUTHOR]

Mungbean (Vigna radiata L.), one of the most widely grown edible legumes in Asia, plays important roles in the improvement of agricultural cultivation systems as well as human diets. As an understudied crop, however, most mungbean varieties are characterized by unstable yields, poor disease resistance, and unsuitability for mechanical harvesting, thereby leading to a low production income. We, therefore, developed Jilv 20, a new mungbean cultivar with a dull seed coat, by crossing Bao 942-34 with Weilv 9002-341. After 11 years of selection and evaluation, Jilv 20 has shown wide adaptability, early maturity, high yield, halo blight resistance, and suitability for mechanical harvesting. The growth period of Jilv 20 is 79.5 and 66.7 days in the spring and summer sowing seasons, respectively, and the average plant height is approximately 56.4 cm. In this study, average yields were 1737.9, 1532.3, and 2045.1 kg/hm2 in northern spring-sowing, northern summer-sowing, and southern sites, respectively; these values were respectively 27.83%, 28.48%, and 6.96% higher than those of control cultivar Zhonglv 5, which has been popular in past decades because of its wide adaptability. The average protein and starch contents of Jilv 20 seeds were 25.0% and 49.56%, respectively. Further application and extension of Jilv 20 in China should contribute to mungbean production, breeding, and industrial development. [ABSTRACT FROM AUTHOR]

RE2Ti2O7 (RE = Y, Yb, Ho, Er) pyrochlores are very interesting as potential candidates for host materials for applications in transition-metal ions lasers. Y2Ti2O7 crystals were grown by the optical floating zone (OFZ) method. The shape of the growth interface is of paramount importance for the growth of single crystals. As striation and the growth interface have the same shape, we observed the striations in as-grown crystals under polarized light. The degree of overheating of the molten zone influences the shape of the growth interface. An increase of power supplied to the molten zone combined with a decrease of both, thermal conductivity and the amount of heat dissipated by the seed-rod, causes an increase in the degree of overheating of the floating zone. Under a high degree of overheating, the interface of the crystal grown is less convex, with smaller curvature. With the speed of rotation of these crystals decreasing from 30 to 7 rpm, the curvature of striations decreases and the shape of the growth interface changes from convex to less convex, and finally to concave. [ABSTRACT FROM AUTHOR]

Due to the existence of a hard and massive roof (HMR), severe ground pressure behaviors have been observed at the working face, resulting in safety issues and the degradation of production effectiveness. Based on the HMR conditions of the Datong Mining Area, the fracture-related instability of the HMR and its effects on the support selection were investigated by analyzing the interaction between support and overlying strata. Advancefixed-distance presplitting blasting (AFPB) technology was proposed to control the caving interval of HMR, and the influence of the controlled interval on the working load of supports was also analyzed. The working load of the support and the caving interval of the HMR were determined based on the controlled HMR fracture technology, and these were verified by field application tests. The working resistance of the support and the step distance were determined based on controlled roof fracture and were verified by on-site application experiments. The results revealed that cracks emerged after the presplitting blasting, resulting in significantly reduced strata behaviors. Furthermore, the support exhibited good adaptability. [ABSTRACT FROM AUTHOR]

The large mining height fully mechanized top-coal caving mining technique has developed rapidly and become the most extensively used mining method for ultra-thick coal seams. The arching of coal/gangue and the drawing out of gangue are peculiar phenomena in the process of fully mechanized top-coal caving mining, which not only affects the recovery of top-coal, but also affects the quality of the coal. This paper studies the arching phenomenon in top-coal caving mining process of ultra-thick coal seam. A series of laboratory granular material simulation experiments were performing and a top-coal arching model in the framework of mechanics was established to explore the formation characteristic of arches and their effects to top-coal loss. Then the countermeasures against the arches and technology path of intelligent mining based on improving top-coal recovery were put forward and performed in practice. The results show that the recovery ratio of top-coal has increased nearly 6%, and increased the production efficiency at the same time. The research on arching mechanism and removing strategies of dynamic random arches effectively improves the efficiency of fully mechanized top-coal caving mining in ultra-thick coal seams, and provides the foundation for the realization of intelligent top-coal caving mining technology. [ABSTRACT FROM AUTHOR]