Table of Content

15 July 2013, Volume 30 Issue 4

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Study on mechanism of anchor beam arrangement mode based on calculating confining pressure of 3-D roof

LI Wei-teng, LI Zhi, LI Shu-cai, JIANG Bei, MEI Yu-chun, WANG Qi, WANG De-chao, WANG Hong-tao

2013, 30(4):  475-482. 

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To analyze the mechanism of different anchor beam arrangement, the 3D mechanical model of support system acting on roof was established, based on the research of strength in the post-peak region of surrounding rock under low confining pressure. And the confining pressure computing formulas of the roof under the independent action or combined action of bolts, anchors and anchor beam with different arrangement modes, were derived. Calculations of four layout plans of the yielding anchor rope box girder in the 1 000 m deep well of Zhaolou coal mine were analyzed. It is found that after the comparison of confining pressure values and distribution range, among the four programs, the confining pressure state formed in roof surrounding rock with a longitudinal-lateral program was the best, the longitudinal single anchor beam program following, and the last two were longitudinal double anchor beam program and cross anchor beam program. The preferential order of the layout plans corresponds to that of the support effect of different support programs in field test. The mechanism of different anchor beam arrangement modes is that the difference of confining pressure states in roof made by different programs was significant, and the confining pressure state, which had a positive correlation with support effect, was an important influencing factor for support effect of program.

Mechanical characteristics of confined grouting reinforcement for cracked rock mass

ZONG Yi-jiang, HAN Li-jun, HAN Gui-lei

2013, 30(4):  483-488. 

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In this paper, based on the uniaxial compression test of intact rock samples, the confined grouting reinforcement of cracked rock samples were carried out, and the mechanical properties of grouting reinforced samples were also tested by using self-made grouting system. Meanwhile, the microstructures of cracked rock samples before and after grouting reinforcement were observed by KH-3000 Videomicroscopy. The results show that there are a lot of interpenetrated fissures in cracked samples, and the fracture mechanisms of samples are mainly the tensile failure. Compared with residual strength, the strength of grouting reinforced samples are increased at different degrees due to the filling and consolidation of fracture planes, but the strength recovery coefficient is not high. In addition, the confined grouting reinforcement can promote the transformation of cracked rock samples deformation from brittleness to ductility, and make the lateral and vertical deformation tend to coordination. Moreover, the confining pressure has great effect on grouting amount, radial stain, strength of grouting reinforced samples and strength recover coefficient, and the reinforcement effect can be improved significantly by increasing the confining pressure.

Creep simulation on fractured surrounding rock of large section chamber and its control technology

WEI Si-jiang, GOU Pan-feng, YU Chun-sheng

2013, 30(4):  489-494. 

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To large section chamber with fractured surrounding rock and repeatedly repairing, strong rheology cannot be controlled effectively with bolt-wire-cable support style. According to the repeatedly repairing 39# pump house of Zhongmacun Colliery, Jiaozuo Coal Company, the main factors on instability of surrounding rock include strong rheology strata influenced by high stress, uneven loading on steel timbers. Repair scheme combined initiative and passive support is proposed, which includes primary bolt-wire mesh-cable, secondary closed steel timber and third grouting reinforcement. Original and repairing support is analyzed with creep numerical simulation. The results indicate that shrinkage percentage of chamber section is 92.2% within 360 days, and the maximum roof subsidence is 2 792 mm, and accelerated creep phase of surrounding rock appears. The maximum roof subsidence is 56.8 mm within 1 000 days, and stable creep phase of surrounding rock appears with repairing method. Cables are anchored in intact rock mass, but most bolts are in plastic zone. Density of stress contour lines is very intensive outside of grouting range, whose peak value is increasing and moving gradually to deep surrounding rock with the extension of time. The field experiment shows that maximum displacement of chamber is 18 mm, and convergence ratio is less than 0.5 mm/d after 224 days. So the repair scheme of the chamber is successful.

Study on influence law of in-situ stress in deep underground rocks on the size of failure zone in roadway

YANG Xu-xu, JING Hong-wen, CHEN Kun-fu, WANG Wen-long

2013, 30(4):  495-500. 

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In order to study the influence law of deep underground in-situ stress on the size of failure zone in surrounding rocks of mining roadway，an in-situ stress measurement was conducted under Yuncheng one kilometer-depth mine by means of hollow inclusion gauge method, and the in-situ stress state around the shaft station was obtained. Then the sizes of surrounding rocks’ failure zone in the walls of different roadways were measured with acoustic wave. The in-situ stress was transferred into initial radial stress and initial shearing stress on the vertical walls’ parallel sections. Through comparing the sizes of failure zones under different initial stress state, it was discovered that the influences of initial radial stress on failure zone in surrounding rocks were remarkable and the range of failure zones would be smaller with higher initial radial stress. Nevertheless, the influences of initial shearing stress were much less obvious. Besides, the measuring results also confirmed that the property of surrounding rocks and the size of roadway section were significant factors influencing the dimensions of failure zone.

Influencing laws study of depth of gully on dynamic strata pressure of working face in shallow coal seams

ZHANG Zhi-qiang, XU Jia-lin, LIU Hong-lin, LI Hu-wei

2013, 30(4):  501-505. 

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Based on the dynamic strata pressure accidents happening when the working faces passed gully terrain in Huojitu coal mine of Shendong mine area, this paper has researched the influence laws of depth of gully on dynamic strata pressure of working face in shallow coal seams with the methods of theoretical analysis and numerical simulation experiments. The result indicates that the deeper the depth of gully is, the greater the possibility of being eroded by the primary key strata (PKS) is. When the working face meets the gully terrain, because the eroded PKS block can not form the stable bond-beam structure but cause instability, which will make the sub-key strata (SKS) blocks support increase load rapidly, it will cause dynamic strata pressure disasters and accidents on the working faces. Conversely, if depth of gully is shallow and the PKS block is not eroded, dynamic strata pressure accidents will not happen on working faces. Theoretical analysis and simulation results fit the in-situ measurement well.

Overburden failure laws in working face of short distance thick coal seams group

XU Yan-chun, LIU Shi-qi, LIU Zhao-xing, ZHANG Qi, WANG Huan-zhong

2013, 30(4):  506-511. 

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In this paper, to deeply study the overburden failure rules in sub-level caving mining of close distance thick coal seams group, and provide basis for the reasonable setting of safety coal and rock pillars in the outcrop area to control the water disasters (e.g.water inrush, sand inrush) occurred in shallow part coal face, taking one working face in close distance thick coal seams group (No.7 and No.8 Coal Seams) of Datun Mining Group as example, on the basis of early observation of overlying strata failure rules in the upper coal seam (No.7 Coal Seam), the underground “two zones” visualizer was recently used to observe the “two zones” height development characteristics of the lower coal seam (No.8 Coal Seam), thus taking the leading and comprehensive measurement of overburden failure laws in the working face of close distance thick coal seams group in China. The results show that when there exits coincidence area between the floor damage range of the upper coal seam and the caving zone development range of the lower coal seam,the caving zone height of the lower coal seam will increase.Meanwhile, the ratio of the fractured zone height to the mining height in sub-level caving mining of close distance thick coal seams group is similar to that in the one single coal seam according to the calculation of comprehensive mining thickness, while the ratio is higher than that in one single seam about 52% according to the calculation of lower coal seam thickness. Therefore, the calculation formula of “two zones” height in “Mine regulations in three special conditions” needs further improvement under the conditions of sub-level caving mining in the close distance thick coal seams group.

Research on granular flow laws of caved ore and rock for steeply dipping thin vein

XU Shuai, AN Long, FENG Xia-ting, DONG Jin-kui, LI Yuan-hui

2013, 30(4):  512-517. 

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Based on the geological conditions and ore-rock physical properties of a gold mine in Inner Mongolia, the numerical simulation research of granule flowing laws of the steeply inclined and narrow veins is analyzed by using discrete element method of the particle flow. The results of the analysis show that the flow patterns of particle can be divided into side wall control zone, transition zone and free fall zone. The patterns of stress transmission can be divided into homogeneous stress zone, decompression and unstable arches. Based on what is mentioned above, the author analyzes the effect of the changes of ore friction angle on ore drawing process, especially the effect on the size of dilution triangle ore body and contact force between particles in ore drawing process. The results of the analysis are as follows: 1) The greater the ratio of the friction angle δ and the friction angle φ of ore is, the bigger the dilution triangle ore body will be; 2) The greater the friction angle of particles is, the more frequent the production and collapse of the unstable arches will be and the easier to produce stable arch. Based on the research results, a method of optimizing the mining structural parameters and reducing the ore loss and dilution is put forward.

Deformation and failure mechanism of mining floor in “three-soft”coal seam based on field measurement

ZHU Shu-yun, ZHOU Hai-yang, LI Xin-fang, YANG Chao-wei, SUN Qiang

2013, 30(4):  518-525. 

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To research the deformation and failure mechanism of “three-soft” coal seams under blasting mining conditions in Zhengzhou mining area, by comprehensively using field measurement，theoretical analysis and numerical simulation, the deformation and failure depth and mechanism of mining floors in a typical coal face in Gaocheng Coal Mine were studied in this paper. The deformation and failure depth and stratum in the roadway floor of the “three-soft” coal seam, as well as the width and influence scope of peak stress ahead of the coal face were obtained by analyzing the monitoring data of strain sensors in boreholes at the haulage and ventilation roadways. On this basis, the engineering geological model for floor stress calculation was established, and the analytical solution of basic strain and the distribution law of deformation and stress in mining floor at different depths along with the face advancing were deduced and simulated by theoretical analysis and numerical simulation.

Match between the solidification of the cemented backfill and the vertical stress in the excavated ore body

LIU Yu-long, DING De-xin, LI Guang-yue, HU Nan

2013, 30(4):  526-530. 

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Samples, with slurry concentrations of 78%, 80% and 83%, cement-tailing ratios of 1∶6, 1∶8, 1∶10, 1∶15, 1∶20, 1∶25 and 1∶30 and different curing time, were prepared by using the neutralized uranium tailings from heap leaching as the aggregate, and the uniaxial compressive strengths for the samples were measured. The relationships between the cemented tailings strength and the curing time were established by experimental data fitting. The results showed that the mechanical parameters for the relationships, such as final strength of cemented tailings, strength response factor, time needed for strength stability and primary strength (t=3) can quantitatively describe the variation of the cemented tailings strength over the curing time. Energy match coefficient was proposed to show the energy density relationship between the excavation and the backfill deformation. Calculation equation showed that the reasonable match time correlated closely with volume density of rock mass, depth of the ore body, elastic modulus of rock mass, cement-tailing ratio, slurry concentration and curing time. This new approach was verified by a uranium mine.

Comprehensive testing and numerical analysis on the failure characteristics of mining coal seam floor

ZHANG Rui, JIANG Zhen-quan, YU Zong-ren, CAO Ding-tao, WANG Zong-sheng

2013, 30(4):  531-537. 

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Based on the condition of the fully-mechanized working face in the mine, the rock deformations that changes with workface advance under different depth of coal seam floor are measured through the strain method. The results show that the violent influent range of mine pressure on the coal seam floor was “advance” appearance and “lag” continuity. The distance of the “advance” appearance was 37 m and the “lag” continuity was 32 m, and the violent influent range of mine pressure on the coal seam floor corresponding is decreasing from the shallow to deep. Combining with the analysis of the drilling sighting glass on mining floor, it is confirmed that the damage depth of working face floor mining-induced was 12 m. Based on the field in-situ measurement, using FLAC3D numerical simulation as a method of making a comprehensive comparative study about the failure characteristics of the coal floor, it reveals the three-dimensional failure characteristics of the floor in the mining process better. Using the field strain measurement, in-situ drilling sighting glass observations and numerical simulations as a mutual authentication method of making a comprehensive comparative study of the failure characteristics of the coal floor, it makes up the disadvantage of single research means in the past.

Study on the time difference from initiating cracking to large area caving of thick-hard roof on shallow Wongawilli face

LI Shao-gang, LI Da-yong, SUN Zhong-guang

2013, 30(4):  538-541. 

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The geological condition of shallow thick-hard roof is very common in Shendong mining area, which would be particularly conductive to form a large area hanging roof especially when the Wongawilli production practice is adopted. If one of the working face sections stopped to limit area, large-area caving zone will come into being on the thick-hard roof, which will result in casualties and equipment damage. In this paper, fracture mechanics theory is adopted to study the cracking of thick-hard roof. Based on energy balance in the process of crack extension, the minimum duration from initiating cracking to large area caving of thick-hard roof on Wongawilli face under ideal conditions without blasting disturbance is derived, and it provides a theoretical basis for reasonable control of thick-hard roof.

Transient effect and mechanism of near magnetic field in impact failure process of coal mass

LI Cheng-wu, WEI Shan-yang, ZHANG Shi-jie, YANG Wei, CUI Yong-guo, JIE Bei-jing

2013, 30(4):  542-547. 

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In this paper, the impact failure experiment of coal mass was conducted in SHPB experimental system. Meanwhile, the changes of near transient magnetic field were tested by ZDKT-1 Transient Magnetic Testing System, and the generation mechanism was analyzed. The results show that the near magnetic field of coal mass will be mutated suddenly when the coal samples were suffered by high speed impact. In addition, different impact damage characteristics of coal mass were comparatively analyzed through infrared spectrum technique. It is concluded that H-bonds of hydroxyl group are changed at different statuses before and after the impact failure process of coal samples, and the separation and transfer of massive electric charge during the H-bonds rupture is one of the most important reasons for instant mutation of near magnetic field.

Research on dynamic calibration method of rock mass strength of mine based on microseismic monitoring

YANG Tian-hong, ZHENG Chao, ZHANG Peng-hai, YU Qing-lei, LIU Hong-lei, NAN Shi-qing , LI Cheng-he

2013, 30(4):  548-554. 

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The strength parameter of the rock mass varies with space and time. Microseismic monitoring datum during the rock mass failure of Shirengou iron mine was processed and analyzed and three parameters (microseismic events number, accumulated energy, average distance between the events) were obtained. Combined with numerical calculation result of stress field, correspondence of microseismic datum variables and stress variables was built by analyzing evolution law of microseismic monitoring datum and stress field datum with underground rock mass failure. Dynamic calibration method of rock mass strength parameter was proposed based on microseismic monitoring datum by parameter inversion, and safety coefficient of underground rock-mass stability was obtained. The results showed that dynamic calibration of rock mass strength parameter is very achievable by analyzing microseismic monitoring datum and the stress field, thus providing a quantitative analysis method for dynamic evaluation of rock mass satiability of underground mine.

The response features of roadway surrounding rock in different hardness coal seams under dynamic disturbance

WEN Ying-yuan, MOU Zong-long, YI En-bing, WANG Hao, LIU Zhen-jiang

2013, 30(4):  555-559. 

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In order to study the influence principles of dynamic disturbance on roadway surrounding rock in different hardness coal seams, the paper numerically analyses the stress response of roadway surrounding rock under dynamic disturbance. The results demonstrate that the average period that the dynamic disturbance has effect on the steady of rock is 0.4 s. The soft coal’s is more serious than the hard coal’s when compared with the horizontal stress amplitude of roof rock and the deformation of roof and side roadway. However, the hard coal’s is more serious than soft coal’s when compared with the vertical stress amplitude of side roadway, the horizontal stress amplitude of floor rock, the deformation of floor rock and the plasticity zone of floor and side roadway. The deformation of roof rock is more serious than that of floor and side roadway in two kinds of coal seam, and in soft coal seam the deformation of side roadway is more serious than that of floor rock. During the increasing period of roadway deformation, the rate of rise is different in side roadway and floor roadway, but is same in roof rock.

On obtaining jointed rock slope geo-parameters and the application of PFC2D

WANG Pei-tao, YANG Tian-hong, YU Qing-lei, LIU Hong-lei, ZHANG Peng-hai

2013, 30(4):  560-565. 

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Safety production of open-pit mine mainly depends on the stability of slope. The first step to investigate the stability of slope by using particle flow code is to obtain a series of reasonable characteristic parameters which are mainly controlled by strength of rocks and distribution of joints. By virtue of a project case in Heishan open-pit mine, one of the iron ore mines of Hebei Iron and Steel Group Mining Company (HBIS), the application of an approach to obtain the characteristic parameters of jointed rock slope is presented in this paper. The strength of rock and distribution of joints were investigated by rock point load instrument system and ShapeMetriX3D system separately. The Hoek-Brown failure criterion is found suitable to estimate geo-mechanical parameters. Then the values are applied to the numerical simulation of PFC2D. Through this study, an vision of where the failure started, how it developed and what the final failure looked like during the process of mining the hanging wall ore is put forward and the simulation results which are similar to the site survey and similarity models give a reference to guide the slope deformation monitoring.

Displacement rate and energy simulation of sandstone under different peak loadings of 0.1 Hz sine wave

LIU Jie, LI Jian-lin, LUO Shi-wei, CAI Jian, XIAO Lei, TANG Liang, TANG Tian-cai

2013, 30(4):  566-572. 

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In this paper, under the premise that the rule of loading rate varying with time has been known, the research results show that there presents a linear relationship between the apparent elastic modulus and the loading force under different peak loadings, in which the first-order coefficient declines and the constant term increases as the growth of peak loadings. This rule is determined by consolidation degree and original clastic cement strength of rock mass. Meanwhile, the predictor formula of displacement rate in millisecond level was put forward, its rationality was confirmed by comparing the calculated dis-placement rate and the observed values. After comparison, it suggests that the peak points of displacement rate in loading areas all appear between 1 000 ms and 2 000 ms, which is 2 500 ms ahead of the peak time of the loading rate, while the peak points of displacement rate in unloading areas appear between 8 000 ms and 9 000 ms, which is 7 000 ms lagging behind the peak time of the unloading rate. It explains that the ‘peak shifting’ phenomenon exists under different peak loadings and the predictor formula can well explain and predict this phenomenon. According to the derivation formula, the energy absorption statistics of rock samples were further carried out, which suggests that the predicted millisecond level energy absorption process under different peak loadings agrees well with the measured process, and the applicability and rationality of the displacement rate predictor formula is further illustrated.

Influence parameter sensitivity of underground mining on rock slop stability

XU Hong, YAO Guang-hua

2013, 30(4):  573-577. 

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To obtain the influence of underground mining activity on rock slop stability, by using numerical simulation and orthogonal experiment, the influencing process of main factor changes ( e.g. coal seam thickness, mining depth, goaf size, relative position between coal face and slop, coal seam dip angle) on rock slop stability and the parameter sensitivities during mining process were analyzed in this paper. The results show that the influence degree of mining activity on rock slop stability increases with the increase of goaf size and coal seam thickness, and decreases with the increment of coal seam dip angle and relative position between coal face and slop. Meanwhile, the influence of mining depth on slop stability firstly increases, then decreases, while mining in the depth between 200~250m.most influence the slop stability. When meeting the production demands, the goaf size control is the best method to reduce the influence of mining activity on rock slop stability.

Experimental study on confined loading-water immersion-unloading of coal gangue

QIAN Zi-wei, CAO Li-wen, JIANG Zhen-quan, SUN Qiang

2013, 30(4):  578-582. 

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Confined loading, creep observations, water immersion, unloading experiments about broken coal gangue which has different water content were performed. The results showed that during the compression process, the stress-compression ratio relation can be fitted as a non-linear curve by exponential function; after the test, the significant particle breakage phenomenon occurred, the non-uniform coefficient increased and the effective particle size decreased and the fragmentation degree of water immersion specimens was greater than that of dry and natural state of waste rock; the axial additional compression occurred to coal gangue after water immersion, the compression rate of this process increased by 9.68%, accounting for 37% of the whole process, “collapsibility” phenomenon occurred; through the analysis, the mechanism of water immersion collapsibility of coal gangue is that, water softening and water lubrication on the coal gangue particles made the particles re-broken and further adjustment of the position, resulting in the coal gangue compact once again.

Temperature effect on strength and damage property of rock mass

LIU Shi, XU Jin-yu, LIU Zhi-qun, ZHI Le-peng, CHEN Teng-fei

2013, 30(4):  583-588. 

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Based on the uniaxial compressive test, the variation laws of longitudinal wave velocity, failure modes, compressive strength and damage property of marble specimens while experiencing different temperatures among 25~1 000 ℃ were studied in this paper. The test results show that there are multiple splitting surfaces along the axial direction of marble after high temperatures, and the split failure mode is the main destructive manner of marble. Meanwhile, the compressive strength of marble increases visibly at 100 ℃and 400 ℃, and then presents deterioration with the increase of temperature after 800 ℃. When the temperature reaches to 1 000 ℃, the marble nearly losses bearing capacity. Moreover, the longitudinal wave velocity declines linearly and the damage increases linearly with the increase of temperature, which reflects the changes to internal nature of marble after the high temperature effects. Rock mass is aggregated with mineral components together, thus, the changes of mineral components under high temperatures, to some extent, can affect the physical and mechanical characteristics of rock mass.

Study on subsidence model based on double-medium mechanics coupling

GU Wei, TAN Zhi-xiang, DENG Ka-zhong

2013, 30(4):  589-594. 

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Based on the analysis of the moving forms of rock damage state, different subsidence models are built respectively according to the relative theories of mechanics of materials and mining subsidence, and the calculation formula of rock movement and deformation under the mining are derived in this dissertation. Through the two medium models of the relevant coupling, this research forms a mining subsidence model of double-medium subsidence space layered transmission. Meanwhile, the corresponding calculation and visualization program are also designed in this study. This model can not only calculate rock and surface subsidence, but also analyze and calculate the damage state and fracture height of rock. The model has been proved valid and reliable by comparison with experimental data.

Range extender of protection and continuous mining technology of protected seam

WANG Hai-feng, CHENG Yuan-ping, LIU Gui-jian, KONG Sheng-li, ZHANG Rui

2013, 30(4):  595-599. 

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The protected area of protected seam is often smaller than the protective seam mining area in the process of mining protective seam and the extraction of pressure-relief gas, because of the different seam inclination, the distance of seams, the pressure relief angle and the coal block. The protected seam cannot be continuous mined. The protective seam can not completely protect the protected seam at the same level in remote inclined coal seam. In the research, those methods can be used to solve the above-mentioned problems. First, the application of intensive drilling gas extraction in oversizing area along strike can increase the pressure relief angle from 56°~60° to 90°. Second, two protective seams can be used to protect one protected seam. Third, deepening the protective seam can completely protect the same level of protected seam. In Huainan and Huaibei mines, the protected seam work-face can be equilong and aequilate arranged by using above methods.

Deep-hole directional static cracking technique for pressure relief and permeability improvement in mining-coal bed

ZHANG Chao, LIN Bai-quan, ZHOU Yan, DI Cheng, ZHOU Chao, SUN Xin

2013, 30(4):  600-604. 

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In this paper, to improve the gas extraction efficiency of soft coal seam with high gas content and low air permeability, combining with proper borehole layout, we have developed a static creaking technique to fracture coal mass and improve seam permeability, and applied to the practice in No.7601 Driving Face of Wuyang Coal Mine. The practice results show that the deep-hole directional static cracking technique has higher depressurization and antireflection effect than that of common ways, which will provide reliable technical guarantee for high efficient gas extraction in soft coal seams with high gas and low air permeability.

Similar conditions of outburst simulation test for rock cross-cut coal uncovering

CHEN Yu-jia, JIANG Cheng-lin, WU Ai-jun

2013, 30(4):  605-609. 

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In this paper, to solve the field inspection difficulties for outburst prediction indicators in rock cross-cut coal uncovering, on the basis of similarity theory and the mechanics condition of outburst, the similar conditions of outburst simulation test in laboratory was analyzed by using dimensional analysis method, and the testing equipment for outburst simulation were designed. By applying similar ground stress and gas pressure on the equipment, the outburst simulation test was conducted. Moreover, all the outburst prediction indexes for rock cross-cut coal uncovering were tested under the same condition, and the accuracy of each prediction index was studied. The study in this paper produces conditions for the laboratory examination of outburs prediction indexes in both rock cross-cut and shaft coal uncovering．

Direct method of determining gas content of coal beds from clastic coal core

WANG Gang, XIE Jun, DUAN Yi, DENG Shuo-gang

2013, 30(4):  610-615. 

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In view of the difficulties to obtain the clastic coal core when using the direct method to determine gas content of coal seam, the mathematic model of gas diffusion in taking clastic coal core was proposed in this paper, and the compensation for the methane desorption model was established by step-fitting calculation. In addition, the direct and rapid measurement method of original coal gas content has been achieved by using deep-hole coring technique and gas desorption method. The practice results show that the measured related factors of gas desorption volume and are basically above 0.99 when using step-fitting method to calculate gas diffusion. Moreover, the gas content and pressure of No.7th, 9th and 10th coal seam in Tongzi coal mine were measured, and the results accord well with the real situation of outbursts occurred many times in these coal seams. Thus, the theoretical and experimental studies mentioned above can accurately calculate gas content in coal seam, and provide a basis for predicting coal and gas outburst when using the prediction index of gas content.

A new prediction index of coal and gas outburst

ZHANG Lang

2013, 30(4):  616-620. 

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At present, the main methods for predicting outburst in China are mainly based on gas dynamic phenomena and the so-called four-parameter method (e.g. gas pressure of coal seam, failure mode of coal mass, hardiness coefficient of coal mass, and initial diffusion velocity of gas). The four-parameter method requires that coal seam should be confirmed as outburst seam only if all of the four parameters exceed their alternative critical values, and the critical value of gas pressure is 0.74 MPa. However, practices show that outbursts had happened even though the gas pressures were less than 0.74 MPa. In this paper, the outburst mechanism was overviewed by compressible fluid mechanics, and a new predicting index F was established by using the stress analysis method of multi-phase continuum mechanics. In addition, calculation method for determining the related parameters was also given. Case studies reveal that the formula accords well with the practice.

Combined drilling of hard rock with abrasive water jet and mechanical bit to improve drilling efficiency

TANG Ji-ren, LU Yi-yu, GE Zhao-long, XIA Bin-wei, WANG Jing-huan

2013, 30(4):  621-627. 

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A dense “boss” in the hole bottom by the conventional drilling in the hard rock requires a more efficient drilling technique with slow bit wear, a new kind of hard rock combined drilling method with the abrasive water jet and mechanical bit is developed in this paper. In this method, it is proposed to introduce the abrasive water jet to erode the “boss” for a “pilot hole”, and then the drilling mechanism of conventional rotating bit is changed to improve the hard rock drilling efficiency. Meanwhile, the mechanism of the new drilling method to improve drilling efficiency in hard rock was revealed by using fracture mechanics theory and energy conservation principle. Moreover, by designing a hard rock breaking bit and a set of hard rock combined drilling equipment system, a series of comparative experiments between the new and conventional techniques were conducted. The results show that the drilling depth has increased by about 63%, the axial force and torque have reduced by about 15% and 20% respectively, and the bit wear is reduced significantly.

Gas emission rate prediction in coal mine by grey and separated resources prediction method

WEI Chun-rong, LI Yan-xia, SUN Jian-hua, MI Hong-wei, LI Jun

2013, 30(4):  628-632. 

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In this paper, to predict the relative gas emission rate in mine, a new grey and separated resources prediction method was proposed, and the mathematical model of gray-separate source prediction was constructed, that is, by the combination of grey and separate source predictions, the grey theory was used first to make long-term predictions for the relative gas emission in mining coal face and the absolute gas emission in drilling face, then the prediction results were substituted in calculation formula of separated resource model for the prediction of relative gas emission rate in the mine. This method has overcome the low prediction accuracy of grey theory and the short-term prediction of separate source method, and has combined the long-term prediction of grey theory with the high accuracy of separate source prediction. Moreover, the calculation steps and mathematical model of gray-separate source prediction method were introduced in detail in this paper, and the accuracy and feasibility of this method were finally verified by engineering examples. Thus, due to its high prediction accuracy, it can realize the medium and long term dynamic prediction of gas emission rate in coal mines.