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The coal wall and floor of the longwall face in the steeply inclined coal seam are prone to damage, which seriously affects the advance of the working face.By establishing theoretical model, bottom friction experiments, numerical calculations, etc., the characteristics of coal seam roof breaking and caving rock sliding are studied, and the coal wall failure mechanism under different coal seam occurrence and mining conditions is revealed. The concrete measures to prevent coal wall damage and floor slip are put forward.The study shows that the caving rock from the roof of the longwall face in steeply inclined coal seams will form different degrees of filling in the goaf. From bottom to top, it forms three sections including "compact filling section", "uneven filling section"and "non-filling section".However, due to insufficient filling in the upper part of the working face, the dynamic pressure phenomenon is obvious, which is likely to cause serious coal wall slab and bottom plate slip phenomenon, and the working condition of the support will also become worse, which becomes the most unstable surrounding rock of the whole working face.The fragile area seriously affects the safe and efficient production of the working face, and is the key area for the surrounding rock control of the working face.The stability of the working floor is significantly affected by the stability of the coal wall.In actual production, it is found that when the coal seam occurrence and mining conditions are different, the coal wall failure generally presents three failure modes: "plastic-flow", "extrusion-slip"and "shear-slip".The use of a pseudo-tilt arrangement at the working face not only can significantly improve the stability of the coal wall and the bottom plate, but also effectively prevent the hydraulic support from falling and sliding, and can also avoid the occurrence of flying gangue at the working face.With the integration of conveyor and the "flexible reinforced coal wall", it is possible to realize the safe and efficient mining of longwall working face in steep coal seam, and effectively solve a series of rock formation control problems faced by the mechanized mining of steep coal seam. [ABSTRACT FROM AUTHOR]

The increase in the cover depth and length of longwall face leads to some drastic changes in mine pressure occurrence and spatial distribution. Such changes result in a great challenge in surrounding rock control. In order to realize an effective control of the abnormal mine pressure occurrences, happening frequently and difficult to be predicted in deep longwall face with ultra-large length,the roof rupture characteristics and support resistance distribution in such a longwall face are investigated. Pre-existing fracture development significantly increases due to the increase of cover depth. The fracture size and orientations obey lognormal and normal distributions, respectively. The main roof with randomly distributed fractures is reconstructed based on such statistical distributions and DFN method. The large length of longwall face increases the probability of the existence of fractures in exposed main roof. Sub-regional rupture model is established for the main roof with one and two fractures, whose limit load-bearing capacities are achieved. The mechanical condition for the occurrence of the sub-regional rupture of main roof and its subsequent migration is achieved using upper bound theory. Spatial distribution of the broken blocks after the main roof fracturing is non-uniform. The block volume in the middle section of the longwall face is small while that of the blocks on two sides of the longwall face is relatively large. Such distribution reasonably explains the non-uniform distribution of the support resistance along the dip direction of the longwall face. The theoretical conclusions are in good accordance with the experimental results and field measurement. [ABSTRACT FROM AUTHOR]

Face fall remains one of the most difficult ground control problems in single-pass thick seam longwall mining which affects the safety and production. The mechanism of face failure is analyzed using Ritz method, and the co-deformation characteristics of the "roof-support-face"system are revealed through the 3 D physical modeling study. The results show that:(1) The proposed face failure mechanism based on Ritz method simulates the top face fall, top and bottom face fall and entire face fall that are typically observed in the field, and the important influencing factors on face failure are determined as coal cohesion,face concentrated load, face movement and roof uniformly-distributed load.(2) The physical model shows that entire face falls occur in a short time under the concentrated load and face movement. The roof displaces linearly in the vertical direction. Roof vertical displacement and face horizontal displacement increase at a large rate.(3) Under the protection of roof support,however,only partial face failure is observed on the face. The roof vertical displacement increases in a step function. The increase rates of the roof and face displacement are significantly reduced. Face maintains its stability in a relatively long time. [ABSTRACT FROM AUTHOR]

The support and surrounding rock relationship is affected by the loose top-coal in longwall top-coal caving mining (LTCC).The dynamic load tests under different particle types,particle sizes,particle packing thicknesses and impact forces were carried out by using the self-developed dynamic load impact test device,and revealed the influence of loose top-coal in LTCC on supports and surrounding rock relationship.It was found that the buffer effect is positively correlated with the particle packing density,that is to say,the buffer effect is more obvious with the larger particle packing density;when the packing thickness is less than a critical value,the impact effect is more obvious with the smaller packing thickness,on the contrary,the impact force gradually decreases then to be stable with the increment of packing thickness;though the effect of buffering dynamic load becomes greater with the increase of particle sizes,the buffer curve fluctuates obviously,which indicates that the impact process is severe.At the same time,the factors such as the condition of coal seam,the properties of loose top-coal and the structure performance of support should be considered in selecting support type,so as to ensure the safe mining. [ABSTRACT FROM AUTHOR]

In response to the fact that rib spalling affects the normal production seriously in large-cutting-height panel, a method for the determination of support capacity based on coal face stability control has been proposed. Taking panel 8101 as a background, a “coal face-support-roof” mechanical model has been established to analyze the relationship between coal face pressure and support capacity. A coal wall stability control experimental frame was designed and a three-dimension similar simulation experiment was conducted. Coal face failure situation with changing support density was analyzed. Meanwhile, the characteristics of these failure situations were studied using numerical simulation. The results show that roof pressure was borne by coal wall and support. Increasing support working resistance can reduce the pressure that acted on coal wall and enhance the stability of coal wall. Determination of support working resistance should base on the coal wall stability control. Support working resistance of panel 8101 was determined as 15 000 kN through a combination of theoretical analysis, similar simulation and numerical simulation, which was confirmed feasible by engineering practice. [ABSTRACT FROM AUTHOR]

In this paper，an overlying strata breakage prediction experiment platform was developed and used to simulate the dynamic load impact in shallow working face with thin-bedrock. A breaking model of roof strata based on the elastic foundation beam model was proposed to calculate the relative position between main roof's breaking and coal wall and analyze the sphere of dynamic loading. According to the mechanical model of roof movement and the stress-strain curve of uniaxial compression tests，the maximum dynamic load and support's contraction were solved under different situations by using the principle of work and power，the criterion of no supports crushing was obtained，and the physical analog simulation result was explained. The results show that the main roof always breaks ahead of its supporting edge，so dynamic load impact often occurs on support. And the maximum load is related to the immediate roof's thickness，the crack's development degree，the support's stiffness and the initial support force and so on. Its value is far greater than the static load on the hydraulic support formed by overlying strata. The physical analogous simulation validated the mechanical analysis results. [ABSTRACT FROM AUTHOR]

Dynamic failure or even rock burst makes it difficult to keep surrounding rock stay in good control in high intensity mining face. Experimental, theoretical and numerical simulation methods are used in this study to analyze geotechnical material failure feature and strain energy distribution formation in the surrounding rock under intense mining activity and,moreover, mechanism of dynamic failure of the surrounding rock is studied. Rock and coal specimens show static failure formation under low loading rate, but it transits into dynamic failure gradually with increase of the loading rate. Geotechnical material belongs to loading rate dependent material which means the stress state may not be subject to the consistent condition. So the rock and coal may present dynamic failure if the loading rate is too high. With increase of the face advancing rate, loading rate of the major principal stress and unloading rate of the minor principal distributed in the coal seam are rising which may lead to dynamic catastrophe of the surrounding rock. Strain energy density of the coal near the void space is high and the energy dissipated by the main roof at the fracturing time lead to sudden growth of the strain energy density in the coal which make coal spalling show dynamic features. The distance between positions of the peak point of the strain energy in the coal seam before and after the fracture of the main roof is the key area of the surrounding rock control. [ABSTRACT FROM AUTHOR]

In terms of the actual impact of rib spalling on production in large mining height coal face，a flexible reinforcement technique of rib spalling is put forwarded in this study. Based on the deformation characteristics of coal face and flexible reinforcement mechanism，the mechanic properties of manila is analyzed by using the drawing experiment. The strength experiment of grouting of broken coal samples is also conducted to study the strength characteristics. The mechanism of coordinated deformation between manila and coal face is revealed by building the constitutive model of “Manila-serous-coal”. The study shows that:the coal face have the characteristics of gradual exposure，without supporting，large deformation. Manila has the characteristics of good extensibility，higher tensile strength and shear strength，and the manila can adapt to the large deformation features of coal face. “Manila + grouting” reinforcement technology can achieve full length anchorage，and the destructive coal face cannot fall under the tension of coir rope，which improves the stability of coal face. The effect of flexible reinforcement technique of coal face is remarkable，besides the cost is greatly reduced，providing a new way to control the stability of coal face. [ABSTRACT FROM AUTHOR]

In order to study the response characteristics of coal and gangue under different illuminance,a coal-gangue image acquisition system with adjustable illuminance was designed, and some coal-gangue image acquisition experiments were carried out. A coal-gangue gray sub-image database was established, and the gray and texture features of the sub-images in the database were extracted. By defining the Normalized Feature D-value Index (NFDI) and training the support vector machine (SVM) classifier,the experimental data were analyzed. The results show that coal and gangue exhibit some different gray and texture characteristics under the same illuminance, and these characteristics change with the change of illuminance. The recognition accuracies of SVM classifiers based on different characteristics are different. When the illuminance factor is taken into consideration, the recognition accuracy of SVM based on gray and texture features is improved. In addition,the SVM classifier based on the multiple features and illuminance fusion shows a good performance, and the recognition accuracy reaches 98. 39%. [ABSTRACT FROM AUTHOR]

The spatial shape of coal-gangue draw body and 3-D distribution of top-coal recovery ratio were studied by 3-D similar simulation experiment and numerical simulation analysis based on the loose medium flow field theory. The results show that the drawing volume of top-coal caving face in near horizontal coal seam with multi-gangue increases from upper face end to lower face end，while the rock-mixed ratio decreases accordingly，and the lower face end has a higher drawing efficiency；the top-coal recovery ratio zoning presents dynamic evolution process along the coal seam's strike direction and periodic distribution along the dip direction；the relationship between volume of coal-gangue draw body and drawing height presents a power function；the top-coal recovery ratio and rock-mixed ratio show the stages of change with the drawing time，and the interval drawing method can improve the top-coal recovery ratio of multi-gangue coal seam. [ABSTRACT FROM AUTHOR]

Taking the extremely inclined panel No.1201 in Dayuan coal mine，Fengfeng group，as the engineering background，the basic problems of the longwall top-coal caving mining technique in extremely inclined and soft thick coal seam were systematically studied. The results reveal that the rational design of shield supports is the first necessity for the successful extraction of coal seams in such conditions. And the roof strata movement law needs to be taken into consideration during shield design. The support capacity is determined by the impact load of the roof strata in the upper part of working face. Meanwhile，the shield supports used in extremely inclined coal seam require enough resistance capacity to bear the lateral compression，which should be determined combining the mining method and top-coal drawing processes. The results also show an obvious asymmetry of the drawing body and the boundary of top-coal in extremely inclined seam. The method of drawing downward segment by segment while drawing upward in each segment was proposed，considering both drawing mechanism of top-coal and the stability of shied supports. By adopting such drawing method in longwall top-coal caving mining in extremely inclined thick coal seam，the negative effects on the supports during the drawing process can be minimized and a relatively high recovery ratio of top-coal can be obtained.To ensure the stability of set-up room，the opening floor was reinforced before the face installation. [ABSTRACT FROM AUTHOR]