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The stability control of support is a technical problem to be solved urgently in steeply dipping thick seam mining. Based on the geological conditions and characteristics of strata behaviors of No. 25221 working face in 2130 Coal Mine, China, the overburden migration law and load characteristics of support is analyzed with field monitoring, and the theoretical analysis is used to research the influence of mining height and roof movement on the load and instability of supports. Results show that the movement amplitude and intensity of the roof and working resistance of support are higher than those of normal mining height face in steeply dipping seam, which is due to mining height increase. When the roof and floor of working face is stable, the critical working resistance of support is less than two times the weight of support. However, with the influence of roof movement, the support will also move with the movement of theroof, which would not disappear with the increase of the working resistance of support. The movement amplitude and instability probability of the support are increased with the decrease of the working resistance of support and the increase of the friction between the roof and the support, the partial loading degree of roof load and mining height. In addition, the probability of rotation instability in large mining height fully-mechanized face in steeply dipping seam is greater than that of falling instability, and this phenomenon will be obvious with the increase of mining height. [ABSTRACT FROM AUTHOR]

To overcome the problems of sharp decrease of hydraulic support’s prop and even emerging support crushing disaster periodically when the fully-mechanized top coal caving mining method is applied for mining the Carboniferous super-thick coal seam in Datong mining area, the methods of theoretical analysis and field measurement were used to study the mechanism of the instability of strata structure in far field for super-thick coal seam mining. The hypothesis that the movement of the "triangle plate"structure in far field impacts the mine pressure in super-thick coal seam working faces was proposed, and the"triangle plate"structural mechanics model for far field key strata broken in the shape of "horizontal O-X"for super-thick coal seam mining was established. Combining the field measurement in Tongxin coalfield, the geometrical parameters for the broken blocks of "triangle plate"structure for far field key strata broken in the shape of "horizontal O-X"were predicted, and the influence of its strike length and rotation degree on the structural stability was analyzed. The results show that this structure was easy to break when a big strike length and a heavy rotation degree of "triangle plate"existed. The floor heave deformation behavior of advancing segments in tailgate on the side of free face of 8202 working face, Tongxin coalfield, indicated the breakage rule for the "horizontal OX"breakage of far-field key strata indirectly. Based on the influential mechanism of the "triangle plate"structure infar field on the mine pressure in working faces, the precautions of presplitting the far field key strata in advance and mining quickly under the "triangle plate"structure were addressed. The research work can provide a reference to the safe and high-efficiency mining and strong mine pressure controlling of faces with large mining height in super-thick coal seams. [ABSTRACT FROM AUTHOR]

The rib spalling is a technical problem to be solved urgently in steeply dipping thick seam mining. Based on the geological conditions and characteristics of strata behaviors at No. 25221 working face in 2130 Coal Mine, the load and instability characteristics of coal wall is investigated by theoretical analysis, numerical simulation, physical analogue material simulation, and field monitoring. Results show that the asymmetry characteristics of mining pressure and strata behavior of large mining height face is higher than that of general mining height face in steeply dipping seam, which is due to mining height increase. Because the inhomogeneous characteristics of the overburden filling are further enhanced, the asymmetric characteristics of the supporting pressure of the coal wall are also obviously increased. During the process of mining, the mechanical properties of coal wall will gradually deteriorate, coal wall crazes and slip body appears. Then the slip body slides along the slip surface, rib spalling emerges, when the surrounding constraints of slip body are relieved or support pressure increases. In inclination direction, the central area is the high incidence area of rib spalling, upper secondary and lower minimum, which is consistent with the asymmetric loading characteristics of coal wall. Besides, in vertical direction, the displacement at the upper part of coal wall is larger than that at the lower part, and rib spalling is easy to occur near the roof area. And under the influence of the gravity tendency component of coal wall, the rib spalling is easy to spread to the upside. On the basis of safety production demands at No. 25221 working face in 2130 Coal Mine, some control measures have been proposed in the paper. [ABSTRACT FROM AUTHOR]

Through field measurement and statistical analysis show that the support load of large mining height working face is generally larger and this is an increasing tendency with the increase of mining height,there is large and small periodic weighting in longwall face,and the static load of thick equivalent immediate roof is the basic load of support of longwall face.Through physical simulation experiments,the mechanism of immediate roof thickness increase and the move upward of hinge point of roof structure at large mining height longwall face are explored,the definition of “equivalent immediate roof” is proposed,and the“double key strata” theory of large mining height longwall face in nearly shallow seam is established.Roof is mainly the “double key strata” structure of large mining height longwall face in nearly shallow seam.According to the gob filling degree by equivalent immediate roof,the double key strata roof structure can be divided into two types including“double voussoir beam” and “blique step voussior beam-voussoir beam”,and the common situation is"blique step voussior beam-voussoir beam"double key strata structure.The model of double key strata roof structure is established,and the mechanism of large and small periodic weighting in longwall face is explored,and the calculation formula of the setting load of support and the support resistance is put forward,which provide the theory basis for the roof control of large mining height longwall face in nearly shallow coal seam. [ABSTRACT FROM AUTHOR]

To master the structure pattern and moving type of key strata is the basis of analyzing mine pressure in a fully mechanized mining face with large mining height. With the theoretical analysis applied，two structure patterns and six moving types of key strata were put forward，and the forming conditions of structure patterns and moving types were given. The two structure patterns include “cantilever” structure morphology in the caved zone and stable “hinged” structure morphology in the fractured caved zone. The six moving types include “cantilever” directly baggy fall type，“cantilever” bi-directional rotation baggy fall type，“cantilever” quadratic rotation baggy fall type，“cantilever-hinge” alternating movement type，“voussoir beam” moving type and “short voussoir beam” moving type. The six moving types of key strata in caved zone were verified by the UDEC numerical simulation method，and the different influence laws of the six moving types of key strata in caved zone on the mine pressure were revealed，which were also verified by the measured data. [ABSTRACT FROM AUTHOR]

Based on a large amount of field observation in the Yushenfu mining area,the roof pressure at large mining height fully mechanized coal face in the shallow coal seam is obtained.The resistance of the large mining height face increases with the increase of mining height,and rapidly increases when the mining height is above 6 m.The dynamic load factor is 1.4 and has little change with mining height.The roof weighting steps are not changed with the mining height,and the first weighting step is 35-70 m,and the periodic weighting step is 9-20 m.The roof caving height is 2-4 times of the mining height.The peak abutment pressure decreases with the increase of mining height,and the peak position is about 2 times of mining height.According to the field observation and physical simulation,it is found that the large mining height causes high caving zone and “thick equivalent immediate roof” which leads to the hinge layer position of main roof structure move upward.According to the gob filling condition by caved immediate roof,the filling condition can be divided into sufficient filling type and general filling type.Based on the general filling condition which is more dangerous,the roof structural model of “high oblique step voussior beam” is proposed,and the calculation formula of the support rated resistance is put forward.Finally,the theoretical calculation formula of support rated resistance is verified. [ABSTRACT FROM AUTHOR]

In terms of lager space of overlying strata movement and strong mining disturbance in working face of top coal caving with large mining height, this paper investigated the ultra-thick seam at Buliangou Coal Mine. The ground pressure behavior and roof movement characteristics of top coal caving with large mining height were analyzed using the methods such as in-situ observation, and theoretical analysis, etc. The mechanical model of the periodic weighting rock failure of main roof of top coal caving with large mining height was established, and the calculation method of hydraulic support working resistance was obtained. The results show that the hydraulic safety valve opens frequently and the roof subsidence speed is fast when the roof periodic weighting occurs, the rated resistance 13 800 kN hydraulic support cannot meet the requirements of roof control. The larger mining space, the thicker immediate roof, and then, the low main roof becomes immediate roof as a cantilever beam and the high main roof forms masonry beam, which called "Up Masonry Beam and Down Inverted Step Combination of Cantilever Beam". The phenomena of intensive ground pressure, dynamic loads and short duration are due to the structure of "Masonry Beam" sliding instability, which determines the hydraulic support working resistance. [ABSTRACT FROM AUTHOR]

Fully-mechanized top coal caving with large mining height is the main mining method for extra-thick coal seam. However, as the height of coal cutting and coal caving increases, prominent problems such as severe mine pressure behaviour severe rib spalling in working face, low top coal recovery rate and high gas emission rate and so on emerge. Based on the analysis of the development history of the fully-mechanized top coal caving in China, taking the working face 8105 at Tashan Coal Mine as the engineering background, authors studied the movement characteristics of the top coal and roof at the fully-mechanized top coal caving face with large mining height in the 14-20 m extra-thick coal seam, successfully developed key technologies such as the comprehensive prevention and control technology for rib spalling at the fully-mechanized top coal caving face with large mining height, high-efficient coal caving technology with high recovery rate and safety guarantee technology for mining under the condition of "low gas occurrence, high gas emission", etc. The underground test showed that the recovery rate at the fully-mechanized top coal caving face with large mining height 8105 at Tashan Coal Mine reaches 88. 9% which is 5.9% higher than that at working face 8104, the average operating rate of the equipment at the working face reach 92.1 %, and the raw coal produced at the face in 2011 reach 10.849 Mt, which achieve the objective of 10 Mt coal produced at the fully-mechanized top coal caving face with large mining height using domestic equipment in a year. [ABSTRACT FROM AUTHOR]

The average thickness of the overlying bedrock of Longgu primary mineable coalseam is less than 200 m, but there is a thick alluvium averaging above 700 m above the bedrock. The bearing characteristic of fully mechanized longwallcaving face with large mining height on the condition of unloading, the possibility of step sinking and its critical thickness are analyzed in order to solve the problems of the mine pressure at mining face and strata control under-thick alluvium condition. The results show that, while its bearing capacity is not strong after large excavation under the bottom of deep alluvium and its weight is loaded on the underlying bedrock, the fracture zone can form a stable mechanical bearing structure when the thickness of the bedrock is more than 120 m, so the coalface roof can be controlled. On this basis, ZF15000/23/43 hydraulic support has been developed, with the largest working resistance in China. With this hydraulic support, the surrounding rock in fully mechanized caving coalface with large mining height underthick alluvium can be controlled. [ABSTRACT FROM AUTHOR]

There are a number of challenging technical issues in mining the first seam with a high cutting single pass longwall method in thick and multiple gassy seams of short intervals in the western region of China. These issues include the stability of retained gateroads and the quantification of the extent and degree of destressed zones in surrounding strata. To gain an insight of these issues, a theoretical and numerical .study was undertaken for a 4.2 m cutting height face to understand the propagation and evolution of fractures around the face, to characterize the fracture distribution, and to map out the zones of high gas concentrations in the goaf. Based on these findings, a group of large diameter (φ = 250 mm) boreholes drilled into the zones,instead of conventionally expensive gas drainage tunnels, are successfully used to capture the goal gas. A total of 11. 669 5 million cubic meters gas is captured with the boreholes, a total of 677 000 tons of coal is efficiently extracted without any gas issue, and integrated coal and gas extraction is achieved. [ABSTRACT FROM AUTHOR]