Journal of Mining and Safety Engineering

Stability of main roof structure during the first weighting in shallow high-intensity mining face with thin bedrock

WANG Jia-Chen, WANG Zhao-Hui

2015, 32(2): 175-181.

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For achieving better surrounding rock control in shallow working face, the mechanism of abnormal overlying strata behavior such as large-scale shear-caving along the rib is analyzed in this paper. The scale between the height and the length of key block increases because of the increase of the overburden load, mining height and the length of working face. Limit position of rotary instability is obtained according to the principle of minimum potential energy. The slope of horizontal extrusion pressure curve decreases while the slope of the height of articulated surface increases in the turning process of the key block because of increasing of the scale between the height and the length, and the allowing rotation angle before the hinged structure turning to the limit equilibrium position also increases, which is not likely to cause rotary instability of the hinged structure. However, sliding instability is apt to occur. According to the specific instability form of shallow high-intensity mining face, dynamic method for the determining of the supporting resistance is put forward, then first weighting of 31402 working face in Wulanmulun Mine is analyzed.

Rock deformation and support bearing characteristics in reversed fault zone with strata pinchout

WANG Chen，TU Shihao，TU Hongsheng，BAI Qingsheng，CHEN Guanshen

2015, 32(2): 182-186.

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In view of the technical problem of rib spalling when coal face crossing the reversed fault, based on geological and mining conditions in 3204 working face of Zouzhuang coal mine, violent and gentle movement areas of overburden strata with high pressure influenced by reversed fault were studied by using numerical simulation and field measurement, and the characteristics of fault activation advanced coal face and rib spalling around fault was revealed. In addition, according to field measurements of support resistance in higher and lower pressure areas of reversed fault, the pre-reinforced distances for Reversed Fault JF23, JF21 are about 22 m, 34 m respectively, which is consistent with the numerical simulation results. Moreover, by installing scalability beam in hydraulic support, the technical problem of rib spalling was solved effectively. The results provide theoretical basis for pre-reinforced distance determination and support adaptability evaluation when face passing through reversed fault zone.

Vertical slice model for coal wall spalling of large mining height longwall face in shallow seam

HUANG Qing-Xiang, LIU Jian-Hao

2015, 32(2): 187-191.

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By using UDEC software, we have simulated the coal wall deformation and spalling processes when the mining heights of longwall face in shallow seam are 4，5，6，7 m，respectively, and found that the coal wall spalling of large mining-height presented “vertical slice” failure feature. Then, the vertical slice mechanical model was set up. The results show that the most easily spalling position is at the 0.6 times of mining height through the deflection analysis of vertical slice. In addition, with the increase of mining height, the width of coal wall plastic zone, the vertical slice number, and the horizontal deformation of vertical slice will increase, while the stability of vertical slice will decrease. The stability of coal wall can be effectively improved, and the coal wall spalling will be well controlled, by enhancing the roof support, speeding up the mining speed, protecting the coal wall properly, and improving the constraint conditions of coal wall vertical slice.

Simulation of interaction between mine-induced stress and stress of collapse column with fully-mechanized working face advancing

HAO Bing-Yuan, ZHANG Yu-Jiang, QI Ting-Ye, FENG Guo-Rui, BAI Jin-Wen, ZHANG Min, KANG Li-Xun

2015, 32(2): 192-198.

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To ensure the safe passage of the collapse column in the fully-mechanized top-coal caving mining face, the numerical simulation of the interrelation between the mine-induced stress and stress of collapse column was conducted. The results show that the interaction effect between the mine-induced stress and stress of collapse column can be divided into three stages: weak sub-stage, medium sub-stage and fierce sub-stage, the range of whose distance between the working face and the collapse column are 150-100 m, 100-50 m and less than 50 m respectively. Focal points differ in these three stages: in the weak sub-stage, the collapse column should be pre-reinforced, when the mine-induced stress begins to exert an effect on the stress of the collapse column; in the medium sub-stage, the stress of the collapse column starts to impact the mine-induced stress; and in the fierce sub-stage when the interrelation becomes fierce, the roof management should be strengthened. According the above research, the supporting range of roof in the K8403 working face, and the time and strength of the collapse column pre-reinforcement were identified. Meanwhile, the field practice showed that pre-reinforcement of the collapse column had a positive effect and ensured the safe passage of the collapse column.

Investigation into strata behaviours and ground control of high height rotary longwall mining in large inclined angle coal seam under complicated geological conditions

YANG Ke, LU Wei, PAN Gui-Ru, SUN Li

2015, 32(2): 199-205.

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Aimed at complicated geological conditions of large inclined angle seam with soft coal, soft roof, and soft floor and difficulties for ground control in rotary and full-mechanized longwall mining with high height in Panbei coal mine, field observation and numerical simulation have been used to investigation into strata behaviors of No.12124. Based on strata behaviors analyzing, the ground pressure mechanism have been opened out with longwall and high height rotation mining in complicated geological and technical conditions. During the process of rotary mining, with the mining-induced stress affected after No.12125 longwall panel mined, the co-action of abutment pressure concentration developing and powered support periodical supporting is the key factor to result in roof fracturing, roof falling, coal collapsing in working face, and large deformation of entries’ surrounding rocks. Some technique have been implemented and practiced, which mainly includes as follows：to pave network and use steel beams to strengthen the roof salability; to apply anti-skid jack to connect hydraulic support to conveyor and advancing jack to control the decline of conveyor; to use bolting-wire-mesh to control stability of entries surrounding rock in rotation areas; to reinforce timbers to control stability of entries advanced about 10 m to working face. Engineering practice show that research plays an important role in safely mining and provides technologies for rotation mining in complicated geological conditions.

Study on the height of water flowing fractured zone based on analytic hierarchy process and fuzzy clustering analysis method

YANG Guo-Yong, CHEN Chao, GAO Shu-Lin, FENG Bo

2015, 32(2): 206-212.

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Based on the analysis of the factors influencing the height of water flowing fractured zone of roof, mining thickness, mining depth, and working face length, compressive strength of rock and characteristics of rock assemblages have been studied and the corresponding influence indexes have been quantified. Then the weight of the factors has been studied through the analytic hierarchy process and the height of fractured zone has been clustered by the fuzzy clustering analysis method. The result of the study of 10 working face data shows that the mining height is just one of the main factors influencing the height of water flowing fractured zone, with several other factors having an effect on it as well. The research results basically equal the empirical values and measured values. So it is a reasonable study method through which the height of water flowing fractured zone of coal seam roof can be predicted for coal mine.

＂Three fields＂evolution of water inrush process under high confined water in stope floor

SHEN Rong-Xi, QIU Li-Ming, LI Bao-Lin, KONG Biao, NIU Yue

2015, 32(2): 213-218.

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Mine confined water is a serious threat for the safety production of underground coal face. Through theoretical analysis, a mechanics model of crack tip was established, the equilibrium equation of fracture mechanics was deduced, and the crack propagation condition of floor water inrush caused by mining on high confined water were analyzed. In addition, evolution process of rock stress field, damage field and seepage field under mining were simulated by RFPA, and the mechanism of confined water inrush was further revealed. The results show that the propagation condition of water flowing crack is that the resultant force of pore water pressure and t in-situ stress should be greater than the internal cohesion of coal-rock mass. Surrounding rock stress distribution has been changed by mining activities, which also causes local stress concentration and damage within coal-rock mass. After a large-scale water inrush appears, the principal stress is significantly larger than that in crack initiation. Duo to internal damage, the permeability of coal-rock mass increases, and the affected area of seepage field also increases.

Water and sands bursting mechanism induced by geological borehole and control measures

ZHANG Bei, ZHANG Gui-Min, ZHANG Kai, CHEN Yan-Long, ZHANG Guang-Hui

2015, 32(2): 219-226.

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Taking Longde coal mine as example, based on particle flow and liquid flow theories, sand bursting funnel model and water bursting nozzle model were introduced to study the flow calculation model, the mechanism of water and sands bursting and control measures in Longde coal mine were proposed. The results show that compared with the sand bursting funnel model, the flow predicted by water bursting nozzle model is more consistent with the speculate result in Longde coal mine, which means that the model can better reveal the formation mechanism of water and sands bursting. According to the water bursting nozzle model, the aquifer thickness and borehole diameter are the two dominant factors which influence the bursting flow. Based on the constructed dynamic surface subsidence model, the central sedimentation value of surface sand inrush funnel, and the influence radius increase with time, but the acceleration decreases gradually. Prevention method that geological borehole should be investigated and plugged for prevention before the mining d esign has been developed, while a control measure that gradually changing the pipeline flow into fracture flow and pore flow, and finally implementing grouting and plugging has also been proposed.

Research on bearing capacity and burst proneness of coal samples from western shallow-buried coal seam

SU Hai-Jian, YIN Qian, JING Hong-Wen, ZHAO Hong-Hui

2015, 32(2): 227-232.

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Shallow buried depth, thick coal seam and narrow coal pillar are typical occurrence characteristics of western shallow-buried coal seam in China．The uniaxial compression test of coal samples in water-saturated and air-dried conditions, in four temperature levels between 25 ℃ and 250 ℃, and of three different kinds of ratio of height to diameter has been conducted respectively in order to investigate the influence law of temperature, water, and dimension on the bearing capacity and burst proneness of coal samples from western shallow-buried coal seam．The results show that: 1) From natural state-water saturation-seasoned state, peak strength and the modulus of coal samples decrease sharply while the peak strain increases gradually．The damage extent becomes more and more severe while the burst proneness weakens. 2) With the gradual increase of the temperature, peak strength, peak strain and the modulus of coal samples all first increase then decrease, and all arise the critical point when the temperature is 100 ℃, at this time burst proneness of coal samples aggravates with severe splashing during the loading process．However, both the bearing capacity and burst proneness weaken gradually as the temperature continues to rise to 250 ℃. 3) With the increase of the ratio of height to diameter, peak strength, peak strain and the modulus of coal samples all show the attenuation trend．Deformation and the damage extent weaken while the burst proneness strengthens.

Research on stability of open-off cut surrounding rock with thick coal roof and its reasonable anchor cable configuration

HE Fu-Lian, BAO Yun-Shan, XU Zhu-He, LI Er-Peng, XU Lei, LI Tong-Da

2015, 32(2): 233-239.

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To solve the surrounding rock control problem of open-off cut with large section and thick coal roof, the simulation software FLAC3D has been firstly used to study the effect produced by the thickness of coal roof and width of open-off cut on failure characteristic of surrounding rock. The result shows that the coal roof plastic zone is on the shape of rectangle when the coal roof thickness is less than 6 m, and arch when the thickness is more than 6 m. Besides, with the growth of open-off cut width, tensile failure area of roof approximate linearly increases from 4.5 m2 to 14.5 m2. Furthermore, the demarcation point of subsidence speed in roof rock moves up from 4 m to 8 m that are away from open-off cut roof. Then, on the basis of above research, the reasonable configuration is studied by means of mechanical theory analysis, and the jointed "cross stride" control technique is put forward as well, which achieves successful application in field.

Study on the law of slurry diffusion within roadway surrounding rock during the whole section bolt-grouting process

HUANG Yao-Guang, WANG Lian-Guo, LU Yin-Long

2015, 32(2): 240-246.

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In response to the effects of roadway excavation disturbance and grouting pressure decay on the law of slurry penetration and diffusion, an unsteady seepage diffusion basic equation of slurry within surrounding rocks under coupling effect of disturbance stress and grouting pressure has been derived by using seepage flow mechanics theory based on the quasi continuum hypothesis. A numerical calculation model of slurry penetration and diffusion within surrounding rocks during bolt-grouting process has been established by using COMSOL software. The effects of grouting time, grouting pressure and grouting bolt interval on the slurry penetration and diffusion have been systematically studied. The results show that prolonging grouting time can slow down the attenuation of the hydraulic slurry head during the diffusion process, but increase the diffusion radius of the slurry within surrounding rocks at the end. The grouting slurry will form a whole grouting reinforced circle in surrounding rocks when the ratio of grouting bolt interval to slurry diffusion radius is less than or equal to 1.41. Finally, these results have been applied to the design of roadway bolt-grouting supports in the Yuanyi coal of the Huaibei mine. The field monitoring proves that the bolt-grouting method effectively controls the deformation and damage of roadway surrounding rock.

Mechanics and application of four floor heave control technology of deep soft rock roadway in Tingnan coal mine

YANG Jun, SHI Hai-Yang

2015, 32(2): 247-252.

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In response to the floor heave with large deformation of roadway in deep soft rock in Tingnan coal mine, an in-depth study has been done in this paper based on the methods of geological survey, physicochemical test, numerical calculation, in-situ test. The complex deformation mechanism in the west pathway floor heave has been analyzed, and a new technology called “four control and one measure” to transform from the complex deformation mechanism to a simple one has been proposed. In the technology, the roof, two sides, base angle, and floor of the roadway are related to each other as a whole to control the deformation of each position and attain the goal of controlling the floor heave with water control measure. The “four control” includes four countermeasures. First, the anchor bolt is added to the roof and the anchor cable is added to the key position to reduce the stress acting on the floor from the roof. Second, the base angle bolt is used to cut off the plastic slip line of the floor base angle with its own flexural stiffness of the material. Third, the bolts are embedded into the two sides of the roadway to enhance the strength of rock and decrease the width of floor heave. Fourth, the counter-force acting on the inverted arch floor is exerted to bring uniform support and form a closed supporting system. The “one control” includes constructing the drainage in time to avoid the ponding immerging the floor to form floor heave, guniting on the roof and sides to cut off the path of fissure water, and spreading dry lime powder after cutting bottom to close the surrounding rocks of floor. Engineering practice shows that this new technology has effectively controlled the floor heave of soft rock roadway in Tingnan coal mine.

Study on the application of short-hole blasting with guide hole to roof cutting pressure relief of gob-side entry retaining

CHEN Yong, HAO Sheng-Peng, CHEN Yan-Tao, ZHANG Zi-Zheng, WU Li-Fei, LIU Hong-Lin

2015, 32(2): 253-259.

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Roof cutting pressure relief is one of effective ways for optimizing the surrounding rock stress and structure in thick layer of hard roof, and the application of guide hole to roof cutting pressure relief is a new attempt. Based on the mechanism of short-hole blasting for roof cutting pressure relief in gob-side entry retaining, using the combination of LS-DYNA numerical simulation and theoretical analysis, mechanism of guide hole has been analyzed, and the effect of the selection of parameters on the blasting of rock mass has been explored. The results show that free surface of blast hole increases in the guide hole, which affects obviously to the tangential stress, and increases the fracture penetration rate and utilization rate of explosive energy; The guide will give full play to the role as stress concentration when charging hole non-coupling coefficient is 1.31；There is a positively change relationship between maximum tangential tensile stress and guide hole diameter，but it has little effects on the position away from the guide hole. According to the dynamic tensile strength of the rock, the charging hole spacing is determined as 1.2 m.

Study on the properties of TBM surrounding rock large squeezing deformation and its grading

HUANG Xing, LIU Quan-Sheng, LIU Bin, LIU Xue-Wei, CUI Xian-Ze

2015, 32(2): 260-266.

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In order to forecast and evaluate the large squeezing deformation of surrounding rock tunnelling by TBM, the mechanical properties of large squeezing deformation has been analyzed. And large squeezing deformation is defined as a kind of deformation in which deforming speed is high, and the amount of the deformation is large and may exceed the overcut gap between the shield and the surround rock mass, with rate of convergence slow, and time dependence significant. If the ratio between surrounding rock convergence deformation and excavation radius is greater than or equal to 1%, and the ratio between convergence deformation and the overcut gap is greater than or equal to 1, large squeezing deformation will occur. And the squeezing deformation is divided by the above two indexes into five grades: no squeezing, minor squeezing, medium squeezing, severe squeezing and extremely severe squeezing.

Study on deformation and failure mechanism of the tectonic stress areas’ soft rock roadway in Nanshan coal mine

GUO Zhi-Biao, LI Er-Qiang, ZHANG Yue-Lin, DENG Xiao-Wei, WANG Jiong

2015, 32(2): 267-272.

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Based on the site investigation of the tectonic stress area in eastern zone of Nanshan coal mine, the common failure characteristics of the roadway has been summarized in this paper. -120 total return wind roadway has been selected to study the deformation and failure mechanisms, reproducing the deformation and failure process of the soft rock roadway in tectonic stress areas under no support or ordinary bolt net support, by using FLAC3D and studies. The results show that the reasons of roadway damage include high stress, low rock strength and the inadaptaion of the original support to deep soft rock deformation. Finally, combining with the deformation and failure mechanisms, the relationship between surrounding rock and supporting body has been analysed, and their deformation and failure processes has been generalized.

Numerical simulation optimization research of bolt profile configuration with resin full-length anchoring

LIN Jian, REN Shuo

2015, 32(2): 273-278.

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Bolting with resin full-length anchor and high prestress is an effective means to solve support problem of complex and difficult roadway, but its application and promotion have always been restricted due to the construction difficulties. This paper is committed to solving the difficult problem of coal mine roadway full-length anchoring through optimized anchor shape under the premise of the guarantee of anchor performance. The numerical simulation methods have been used to research the relationship between the bolt shape and anchorage bolt performance. Optimized bolt cross rib height is reduced from 1.46 mm to 1.20 mm; bolt cross rib spacing is increased from 11 mm to 30 mm; and the bolt cross rib width is increased from 3 mm to 10 mm. The optimized bolt shearing resistance is reduced by about 50% under the condition of not reducing in the anchorage performance. Consequently, mixing effect is ideal, achieving the goal of the optimization.

Rational buried depth for regulating roadway application during coal face withdrawal in Shendong mining area

ZHU Wei-Bing, REN Dong-Dong, CHEN Meng

2015, 32(2): 279-284.

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In Bulianta coal mine of Shendong mining area, roof fall is tend to happen during the withdrawal of No.12401 and No.12402 coal faces, which is caused by the regulating roadway. To investigate this problem, FLAC3D software was used to study the influence of buried depth on regulating roadway. The results show that the maximum buried depth for regulating roadway application is 213 m to 318 m when the coal pillar is stable, or 165 m to 229 m when the surrounding rock deformation is controllable. By considering other related factors, the final maximum buried depth for regulating roadway application is determined as less than 165 m. The findings have been verified by No.12405 and No.12406 coal faces of Bulianta coal mine, and No.52304 and No.52303 coal faces of Daliuta coal mine, which can provide reference to effective and safe withdrawal of coal faces with similar conditions in Shendong mining area.

Study on combined support technology of bolt-mesh-shotcrete and concrete filled steel tubular supports for soft rock roadway in Yangzhuang mine

LI Xue-Bin, YANG Ren-Shu, GAO Yan-Fa, XUE Hua-Jun

2015, 32(2): 285-290.

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The sounding rock of Ⅲ-Level South Roadway was significantly affected by geological structure, lower roadway sounding rock strength, higher content of clay minerals, and serious argillization. Combined with deformation characteristics of South Roadway, the combined support of bolt and steel tubular confined concrete support (STCCS) has been designed as follows: roadway section is in horseshoe, with Φ20 mm×L1800 mm L-steel bolt, STCCS constituted by Φ194 mm×L8 mm seamless steel tube and C40 core concrete. Combined with theoretical calculation, the ultimate bearing capacity of the designed support programs is greater than the surrounding rock load of South Roadway, which can maintain the stability of roadway surrounding rock. By numerical analysis and on-site monitoring analysis, the final deformation of roadway sounding rock is small after roadway support scheme has been applied. The support force of bolt and STCCS was less than their limit load. Consequently, roadway support is stable and reliable. So the support programs reached the soft roadway support requirement of Ⅲ-Level South Roadway.

Floor heave mechanism and control technology for east rail roadway of Tingnan coal mine

WANG Jiong, HAO Yu-Xi, GUO Zhi-Biao, ZHU Guo-Long, HAN Zhan

2015, 32(2): 291-297.

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In order to solve the floor heave problems in the east rail roadway of Tingnan coal mine, using in-site survey, the physical and chemical composition analysis of surrounding rock, the water softening experiments and numerical analysis methods, the soft rock characteristics, influence factors and deformation mechanics mechanism have been researched. It is concluded that the main reason for the floor heave is mainly due to the strata lithology with weak floor but strong expansibility. Main deformation of roadway and stress release will appear in the bottom when there is no supporting. And the soft rocks in base angle will have large plastic deformation under the stress transfer from both sides of roadway, then extrudes to the center of the floor, forming the floor heave. Hence, corresponding control technology including impermeable base, strengthening, and deformation control is put forward by using the concrete arch-metal welding net-base angle seam pipe bolt support forms. Field monitoring and numerical analysis show that the new support can improve the floor rock mass condition and reduce the base shear deformation.

Rock stability analysis and supporting structure optimization of deep shaft ingate under complex conditions

CAI Hai-Bing, CHENG Hua, RONG Chuan-Xin, SONG Hai-Qing, LI Ming-Jing

2015, 32(2): 298-304.

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In response to such complex conditions as extremely broken rocks, one thousand meters depth, and large size section of new auxiliary shaft ingate in Haizi mine in Huaibei city, shaft ingate rock stability has been analyzed by ABAQUS finite element numerical software for original support design scheme, and distribution law of displacement field, stress field, plastic zone of ingate surrounding rock and mechanical characteristics of ingate supporting structure have been shown. The supporting structure design of ingate has been optimized according to numerical analysis result. Ingate primary supporting structure is composed of bolt, steel mesh, shotcrete and anchor. Ingate secondary support is composed of whole section steel fiber reinforced concrete lining with bottom arch, floor grouting bolt and floor anchor. Strength grade, steel fiber incorporation rate and the optimal mix of steel fiber reinforced concrete have been determined through laboratory tests. Field monitoring results show that ingate supporting structure has higher safety reserve and the design optimization is reasonable.

Bearing characteristic of composite rock-bolt bearing structure under different bolt support density

ZHANG Yi-Dong, CHENG Liang, YANG Jin-Feng, JI Ming, LI Ya-Hui

2015, 32(2): 305-309.

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The composite rock-bolt bearing structure, which is formed by bolts and surrounding rock duo to the interaction of bolt group with reasonable bolt length and density, can play a vital role in the roadway stability control. In this paper, based on self-developed test system of composite rock-bolt bearing structure, the effect law of bolt support density on bearing characteristics of the structure was studied, the actual strength and failure characteristics were measured, and the variation laws of inner stress of composite rock-bolt bearing structure and surrounding rock deformation were revealed. Moreover, the strength of composite rock-bolt bearing structure was further calculated, and the theoretical calculation results are close to the revised measured results.

Research on the effect of concrete heat of hydration on temperature of the outer wall and frozen wall in Cretaceous strata

LI Bo-Rong, XI Jia-Mi, YANG Geng-She, CHEN Xin-Nian, QU Yong-Long

2015, 32(2): 310-316.

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In the process of coal mine shaft freezing sinking construction in Cretaceous strata, through analyzing the monitored data of two representative horizontal layers, the basic law of the temperature variations of the outer wall and the freezing wall has been obtained. Research shows that the temperature increases rapidly after the outer walls have been poured; the temperature of the two horizontal layer rises up to 68.4 ℃ in 1.5 d, and the coarse sandstone’s temperature rising rate of hydration heat effect is faster than that of fine grained sandstone. Amount of hydration heat makes the positive temperature maintenance of the two monitoring levels longer, which can benefit concrete strength at its early growth of the out wall concrete. Meanwhile, the heat causes the frozen wall wide-range temperature rise and partial melting (melting depth reaching 305 mm), which causes negative impact on the strength of frozen wall. The analysis and investigation of the hydrated heat of concrete effection has instructive significance to shaft freezing design and construction in Cretaceous strata.

Experimental study on mechanical properties of coal under high strain rate

LI Ming, MAO Xian-Biao, CAO Li-Li, MAO Rong-Rong, PU Hai

2015, 32(2): 317-324.

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The mechanical properties of coal changing with the strain rate are proposed by impact uniaxial compression tests on split Hopkinson pressure bar (SHPB) equipment which with a diameter of 50 mm. Six different strain rates are provided for coal by designing test pressure levels with 0.30, 0.35, 0.40, 0.45, 0.50 and 0.55 MPa. Results of the tests are indicated as follows：Stress- strain curves of coal at high strain rates can be roughly divided into compaction phase, elastic deformation stage, micro- cracks evolution stage, crack unstable growth stage and unload stage. What’s more, increased strain rate can shorten compaction phase and extended elastic deformation stage. With the increase of strain rate, the increment of dynamic elastic modulus and peak stress of coal can be approximately represented by a logarithmic trend, while decrement of the peak strain approximate logarithmic form. The damage extent of coal sample increases with the increasing strain rate, which becomes the most significant when strain rate increases from 68.666 s-1 to 79.751 s-1.The results can be provided the basis for determining the rationalized parameters of cutting coal mining engineering.

Relation between coal-rock failure and methane emission based on microseismic and dynamic stress monitoring

YIN Yong-Ming, JIANG Fu-Xing, XIE Guang-Xiang, ZHU Quan-Jie, WANG Cun-Wen, WANG Lei, HE Xiao-Jun

2015, 32(2): 325-330.

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Microseismic and stress real-time monitoring techniques were applied to measure coal-rock failures and stress variations during mining process of LW11041 in Fangshan coal mine. Combined with methane emission and methane drainage data, the relation of coal-rock failure, stress variation and methane emission were studied in this paper. The results show that the peak energy of microseismic events occurs earlier than that of extreme coal stress and methane extraction index, while the peak value of methane emission occurs later than that of methane extraction index. Therefore, energy variation of microseismic events can be used to predict coal stress variation and methane emission around the coal face. In addition, the periodic weighting of basic roof is the main reason to result in the periodic changes of methane emission by ventilation. When the basic roof breaks periodically, the methane emission in goafing increases, the methane concentration by ventilation in face also increases, and the methane mainly comes from the methane accumulation in goafing.

Study on top pillar size of transition stope from caving method to filling method based on π theorems

LIU Yan-Zhang, DENG Lei, WANG Qi-Fei, ZHAO Wei, SHI Zhi-Jun, ZHANG Qun, ZHANG Bing-Tao

2015, 32(2): 331-336.

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In the process of transition from caving method to filling method, there is a large scale goaf beneath the top pillar of a filling method transition stope and a large number of loose rocks upon this top pillar. So the stability of the top pillar of the transition stope has a great significance for mining safety. The thickness-to-span ratio of the top pillar is an important factor affecting the top pillar’s stability. The relationship model of the stability and the thickness-to-span ratio of the top pillar of the filling method transition stope have been established with the π theorems to analyze the stability of top pillar. The allowable strain of top pillar has been selected as the criterion of stope stability in the model. According to the allowable strain, the reasonable thickness-to-span ratio has been obtained. This model has been applied to study the size of the top pillar in the test transition stope from sublevel caving method to filling method at Chengchao Iron Mine. The minimum thickness-to-span ratio which is suitable for the engineering condition of Chengchao Iron Mine has been obtained by the finite element method; the maximum thickness-to-span ratio has been obtained by loss rate. As the result of calculation, the thickness- to-span ratio for Chengchao iron is 1.24-1.45. The top pillar instability of the test stope does not happen in the production process. The effectiveness of the model is verified by engineering test.

Stability analysis and rock movement prediction of stope roof below the subsidence area

GONG Jian, HU Nai-Lian, WANG Xiao-Dong, LI Di, CUI Xiang

2015, 32(2): 337-342.

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In order to analyze the stability of the roof below the subsidence area，the RMR rock mass classification and the Q system rock mass classification have been used for rock quality evaluation to calculate the rock condition，and the mechanical model of the subsidence area has been established to analyze the strained state in the roof. The results show that the roof of -127 m level is unstable enough with the mechanical condition of the collapse．The possibility of the collapse of the mined-out area in -127 m level has been verified by the calculation results of the 3D FEM numerical analysis，then the time series predicting analysis has been used for rock displacement deformation．Based on the results of predicting data，the rock movement value of -127 m level increases gradually with the accumulation of potential collapse. Therefore, supporting scheme should be formulated to control the value of rock movement and the time series prediction should be forecasted periodically to monitor the tendency of the rock movement value．

Mining blasting scheme optimization of crown-sill pillar based on AHP-TOPSIS evaluation model

SHI Xiu-Zhi, LIU Bo, ZHAO Jian-Ping, RUAN Xi-Qing, CHEN Hai-Bo

2015, 32(2): 343-348.

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In response to the difficulty in deciding the mining blasting scheme of crown and sill pillars, a AHP-TOPSIS comprehensive evaluation index system model has been established based on the basic theory of analytic hierarchy process(AHP)and technique for order preference by similarity to ideal solution( TOPSIS), and the model has been used to do the comprehensive evaluation optimization for 4 kinds of blasting scheme. 9 indexes have been adopted to comprehensively test the impact on the selection element of blasting scheme from the perspective of economy, technology and security, the weight matrix of the evaluation indexes has been established according to the AHP method, and then the AHP-TOPSIS comprehensive evaluation model has been established with the basic theory of TOPSIS. Finally, the superior degrees of blasting scheme has been calculated based on the comprehensive evaluation index. The synthetic superior degrees of the optional blasting scheme are 50.0%, 62.2%, 69.6%, 45.0%, and consequently the third scheme is confirmed the best (hurn cut; inclined hole and side collapse with an angle of 80°). Research results are consistent with the BP neural network, catastrophe progressing method, and Entropy-Fuzzy Matter-element model, which testifies the feasibility of the AHP-TOPSIS comprehensive evaluation model. It provides a new way to select blasting scheme.

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