Journal of Mining and Safety Engineering

Connotation and prospection on scientific mining of large Xinjiang coal base

ZHANG Dongsheng, LIU Honglin, FAN Gangwei, WANG Xufeng

2015, 32(1): 1-6.

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Xinjiang province, abundant with coal resource, is the 14th modernized large coal base in China. As it is located in arid and semi-arid area, the exploitation of Xinjiang coal base is trapped into the contraction between large-scale mining of coal resource and protection of highly fragile eco-environment. How to efficiently exploit coal resource in conjunction with eco-environment protection is a great scientific issue in Xinjiang Coal Base. This paper focuses on how to study on the connotations, objectives and features of the adaptation of existing mining technology in thick coal seam, the selectivity of high-efficiency mining technology restricted by environmental capacity, the feasibilities of water-protective mining and backfilling mining and the originality of fully mechanized mining technology in giant-thick coal seam and steep coal seam. The preliminary conception and prospection is presented in order to broaden the concepts on constructing green development of large coal base.

Support resistance determination of fully mechanized top-coal caving face in extra thick seam under multi-layered hard strata

LIU Changyou, YANG Jingxuan, YU Bin, WU Fengfeng

2015, 32(1): 7-13.

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In this paper, to clarify the mining pressure behavior mechanism of the coal face in extra-thick coal seam under the multilayered hard overlying strata, and determine the support resistance reasonably, the multilayered roof breaking law and the support resistance in the extra-thick seam were studied, and the determination principle and calculation method of support resistance were obtained, by using the methods of theoretical analysis, similar simulation and field practice. The results show that the breaking form and breaking order of the multilayered hard roof have obvious influence on the mining pressure behavior, and the support resistances corresponding to single-layer key stratum caving and multi-layer stratum synchronous instability are different It will be difficult to meet the support requirements in extra-thick seam by simply improving the support resistance in the condition of multi-layer stratum synchronous instability. Take one coal face in Datong Mining Area for example, though the reasonable support selection in the extra-thick coal seam and using hydraulic fracturing technology for the hard strata, it has achieved good effect for roof control.

Interaction characteristics between strata movement and support system around large mining height fully-mechanized face in steeply inclined seam

XIE Panshi，WU Yongping，WANG Hongwei，REN Shiguang

2015, 32(1): 14-19.

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To research the overlying strata movement around large mining height fully-mechanized face in steeply inclined thick seam, the field measurement, numerical simulation and similar material simulation methods were used to analyze the strata movement, roof structure and rock-support interaction characteristics in this paper. The results indicate that strata movement of large mining height face is similar to general mining height face in steeply inclined seam, which has asymmetry characteristic along the inclined direction of coal face, but the deformation, failure and movement of surrounding rock is more active, roof weighting step decreases obviously and weighting strength increases, while accompanying with rib fall of coal wall. In addition, the space size of slipping, rolling and filling of caving roof increases, and the anti-dip pile structure is easily formed after the fracturing of main roof, while the filling and compacting degree of failure roof increases at the lower part of coal face, which inducing more significant unbalance mechanics features between the upper and lower part of coal face, and the multilevel ladder strata structure is easily formed in overlying strata above the face. Moreover, the characteristics of contacting and loading of roof-support system is more complex, the change range of support load and interaction between supports increase obviously, while the anti-toppling and anti-skid of coal face equipment is more difficult.

Seismic hazard assessment in complex island coalface by computed tomography

CAO Anye, JING Guangcheng, DOU Linming, GONG Siyuan, ZHAO Yongliang, ZHANG Zhenliang

2015, 32(1): 20-27.

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According to the high mining stress and seismic hazard risk in excavation operation of 10305 Island Coalface in Baodian coal mine, the relation between P-wave velocity and stress was analyzed, and the seismic hazard assessment method by using passive computed tomography in 10305 Island Coalface was established. Meanwhile, the indexes of P-wave velocity anomaly and velocity gradient anomaly were proposed to evaluate the stress concentration or seismic hazard zones, and the discrimination standards were also constructed. Finally, the assessment method was applied in 10305 Island Coalface. The results show that P-wave velocity and stress presents characteristics of positive correlation. The high velocity anomalies and velocity gradient anomalies are always located in the regions adjacent to the narrow goafing side of 10305 Island Coalface, which are basically similar to the anomaly areas of seismic hazards. The tomography detection practices show that it is feasible for seismic hazard assessment and anomaly region division during island coalface mining, and the hazard assessment accuracy is high. Thus, the passive computed tomography can improve the monitoring and pre-warning level for seismic hazards in underground mining.

Study on the coupled relationship between AE accumulative ring-down count and damage constitutive model of rock

WU Xianzhen, LIU Jianwei, LIU Xiangxin, ZHAO Kui, ZHANG Yanbo

2015, 32(1): 28-34.

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In order to study the relationship between acoustic emission characteristic parameters and strain, stress and damage variable of rock under different failure models, the tests have been made to obtain the characteristics of acoustic emission of sandstone, leptynite, granite and limestone using hydraulic-pressure servo testing system RMT-150C and acoustic emission instrument SAEU2S under the uniaxial compression. Results have shown that the cumulative acoustic emission ring-down count of rocks with brittle or brittle-ductile failure model increases sharply before the peak stress, while accumulative ring-down count of rock with ductile failure model surges before a quiet period, which can be considered as a precursor for entering failure phase. With time being intermediate variable, the relational model between cumulative acoustic emission and strain generated from rock with brittle, brittle-ductile and ductile failure has been set up, and the coupled relation among cumulative acoustic emission, damage variable and stress has been deduced based on the Weibull distribution constitutive model. Proved by the test data, the precision of constitutive model with brittle, ductile failure is higher, which can provide accurately the basis for rock damage assessment.

Mining methods selection in thick coal seam based on fuzzy analytic ierarchy process

SONG Gaofeng, PAN Weidong, YANG Jinghu, MENG Hao

2015, 32(1): 35-41.

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In this paper, aiming at solving the problem of subjectivity and oneness of the traditional evaluation methods, a new idea of fuzzy analytic hierarchy process was put forward to select mining methods in thick coal seam. Based on the basic principles of fuzzy comprehensive evaluation, in view of the fuzziness and uncertainty of mining method selection in thick coal seam, 4 first level evaluation factors which influencing the mining method selection were determined according to the engineering practice of No. 2 Coal Seam in Dongpang Coal Mine, that is, geological conditions, economic benefits, technical level and safety index, as well as 23 second level evaluation factors. Then, the weights of each first and second level evaluation factors were determined by using fuzzy analytic hierarchy process. The mining method selection in Dongpang Mine were evaluated based on multi-level fuzzy comprehensive evaluation and fuzzy analytic hierarchy process. The results show that the fuzzy membership degree for slicing mining method is 23.19%, and 41.07% for full coal height mining, 35.74% for top coal caving mining, respectively, which indicating that full coal height mining is the best choice.

Experimental study on the changes of coal paste backfilling material performance during hydration process

QI Tingye，FENG Guorui，GUO Yuxia，ZHANG Yujiang，REN Ang，KANG Lixun，GUO Jun

2015, 32(1): 42-48.

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Coal paste backfilling material (CPBM) is composed of coal gangue, flyash, ordinary portland cement and tap water. In order to identify the properties of each raw material, the mineral composition, chemical composition of coal gangue flyash have been analyzed; the compressive strength, porosity and electrical resistivity have been studied at different curing times. The samples taken from curing time of 7 d, 14 d and 28 d, have been evaluated for their mineral composition and microstructure. The law of CPBM property with increasing curing time has been analyzed, and the correlation among the compressive strength, porosity, resistivity and hydrating process has also been deeply discussed. The results indicate that firstly, with the curing time increasing, compressive strength and electrical resistivity are increasing, while porosity and small pore content are reducing. Secondly, hydrated and pozzolanic reaction occur in the change of CPBM property, with calcium hydroxide, C-S-H gel and ettringite being the reaction products. The calcium hydroxide crystal is only found at the curing time of 7 d, not at 14 d and 28 d, and the types and quantities of ettringite crystal at 28 d are more than at 7 d and 14 d. The crystal structure of 28 d presented more slender with the curing time increasing. Thirdly, the hydrated and pozzolanic reaction are the two primary reasons causing the change of performance of CPBM strength with the change of curing time. Moreover，there is some interrelation between the performances.

Stage division and roof structure analysis during fully mechanized caving face passing a collapse column

TIAN Duo, SHI Haoyu, LIANG Xingwang, NIU Guoxing

2015, 32(1): 49-53.

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In this paper, to ensure that a fully mechanized caving face can pass collapse column safely and efficiently, numerical simulation was carried out based on the real mining and geological conditions of No.1 coal mine in Pingshuo coal industry company. Meanwhile, survey lines were arranged to monitor the vertical stress values. The results show that the whole process during fully mechanized caving face passing the collapse column can be divided into six stages according to the vertical stress variation, that is, normal stress stage, stress smooth increasing stage, stress abnormal increasing stage, stress decreasing stage, stress secondary increasing stage, and normal stress recovering stage. Meanwhile, based on the voussoir beam theory, the roof structure characteristics and mechanical properties of the six stages were analyzed, and the roof-supporting measures were proposed correspondingly.

Experimental research on fracture evolution law of water-resisting in coal seam floor during re-mining

FU Baojie，TU Min

2015, 32(1): 54-58.

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North China mining area is affected by limestone water of Taiyuan formation and Ordovician at the bottom of the Permian coal series permo carboniferous coal. In order to analyze the load-transfer characteristics and failure mechanism of the water-resisting floor in response to the dual function of mine-induced stress and water pressure, confined water automatic loading system has been designed, and the failure process of the floor aquifuge fracture initiation, expansion and transfixion has been showed through physical simulation during re-mining. Thus, fracture distribution characteristics and formation mechanism have been presented at the different layers of floor, and through the displacement measurement system, the deformation rules and district characteristics have been drawn.

Formation mechanism of anticline structure and its disastrous mechanism of rock burst

GU Shitan, HUANG Ruifeng, TAN Yunliang, LI Wenshuai, XIAO Zhimin

2015, 32(1): 59-64.

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Aiming at characteristics of rock burst induced by anticline structure, based on material mechanics and theory of Winkler beam on elastic foundation, mechanical model of anticline genesis was establish, the deflection, bending moment and strain energy of the model were deduced. By using UDEC numerical simulation, distribution laws of advanced abutment pressure affected by anticlinal axis were revealed, and surplus energy of E0-Ec at the peak of abutment pressure were studied. Results show that the formation of anticline is influenced by multiple factors. The smaller the buried depth of coal seam, bulk density of overlying strata, characteristic coefficient and foundation coefficient, the larger the tectonic stress, and the easier anticline structure can be formed. In addition, strain energy changes with its locations in anticline structure. The larger the tectonic stress, the smaller the flexural rigidity, and the larger the strain energy in micro-segment dx. With the continuous advancing of working face, the phenomenon of “connection-overlay-separation” of advanced abutment pressure and high tectonic stress of anticlinal axis has been presented. Meanwhile, the closer the distance of working face to anticlinal axes, the larger the surplus energy at the peak of abutment pressure, and the greater the occurrence possibility of rock burst.

Analysis on the catastrophe mechanism of backfill stope resulting from dynamic disturbance

XU Wenbin，PAN Weidong，LIU Hui

2015, 32(1): 65-72.

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In order to investigate the reason of the failure of stage backfill stope during one mine, the deformation characteristics, failure mode of backfill roof and pillar and the surface displacement law of roadway have been studied by similar material simulation, numerical modeling and field monitoring based on the field engineering condition and investigation results. The results indicate that mining action has a significant influence on the stability of the stope and rock surrounding and the engineering on the perimeter zone, and it also poses a different impact on the maximum displacement of stope roof at different sublevel. The incremental quantity of roof displacement reaches the most when mining activity processes at second sublevel. And when mining at the third sublevel exacerbates the stress concentration of pillar, the splitting failure begins to appear along the pillar and the roadway in a structural plane of approximately 60°, and at the same time, the side walls nearby the goaf inside the pillar begin to collapse. Compared to the results obtained from the numerical simulation and field monitoring, the conclusions obtained by similar model test are testified. The research conclusions propose a comprehensive understanding of the reason of the collapse accident, and clarify the potential hazards of backfill stop, which can provide security references for other similar mines.

Study on pillar mining technique for bottom thin coal seam in surface coal mine adopting stripping technology

MA Li，LI Kemin，PENG Hongge，DING Xiaohua，XIAO Shuangshuang

2015, 32(1): 73-77.

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In order to solve the problem of excavating thin coal seam beneath under the condition of casting blast and dragline stripping technology at the bottom of the surface coal mine, the surface pillar mining has been proposed according to working features of stripping technology. The stripping ratio formula of thin coal seam has been deduced, and the optimum ratio of rock height to coal height has been determined, the requirement to work line of the surface pillar mining has been analyzed as well. After analyzing excavating parameters of the pillar mining technology and its application in the 9th coal seam of Heidaigou surface coal mine, the results show that more than 372 thousand tons can be excavated during the working line is 2 200 m, and it can bring 61.28 million RMB. Meanwhile, the approach has a great influence on capacity, and part-length of 9th working line should be discarded when the 6th coal is extracted to the end-slope with considering production capacity requirement and the 9th coal resource recovery.

Stability control strategy of high stress and intense expansion softrock underground openings for pump house in deep mine

WANG Jiong，WANG Hao，GUO Zhibiao，HAO Yuxi，CUI Jiasen

2015, 32(1): 78-83.

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Failure characteristics of the key portions in underground openings used for pump house and suction wells have been analyzed to detect its major control factors and causes, and the stability control strategy has been proposed. The result indicates that the deformation in the underground openings are mainly caused by traditional layout form, the great depth, high geostress, the high level of the horizontal tectonic stress and the high mineral content in the surround rock. The integrated design technique for pump house and suction wells are utilized. It minimizes greatly degrees of the stress concentration and enhances the overall stability of the underground excavations, combined with the counter-measures of anchor cable and truss with the foot grouting anchor pipe for stabilization of deep-buried underground openings. These new techniques have been applied in underground openings for -1020 level horizontal pump house and water suction wells in Kongzhuang coal mine. The in-situ monitoring data plots show that it has achieved very well control effect.

Fast pushing through fault of the pre-driven roadway groups in fully mechanized top-coal caving face with big dip angle

MA Liqiang，YU Yihe，JIN Zhiyuan，LI Jiaming，WANG Guang，LI Yongsheng

2015, 32(1): 84-89.

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For solving the problem of low yield, poor-quality, long duration and low safety factor during longwall face pushing through fault, the technology of fast pushing through fault of the pre-driven roadway groups in fully mechanized top-coal caving face with big dip angle (FMTCFBDA) has been put forward. Considering the fault throw, mining conditions and support stability, the “exceptive horizon” of FMTCFBDA during pushing through fault has been determined and the multiple pre-driven roadways (pre-driven roadway groups) on the horizon has been designed, consequently, working face can directly push through pre-driven roadway groups to cross over the fault. It contains two key technologies: 1) Surrounding rock control technology of pre-driven roadway groups, including pre-driven roadways groups layout, rock pillars size and support parameters, etc; 2) Support stability control technology of FMTCFBDA during pushing through the fault. Considering the strike angle influence on support dip stability and the dip angle influence on support strike stability, hydraulic support instability mechanism has been analyzed during FMTCFBDA in dual inclined state pushing through the fault, the critical support resistance which is less likely to cause topple and slip has been calculated, and corresponding control technology has been put forward. The technology has been applied in 3up1101 FMTCFBDA of Gaozhuang coal mine, and the fault with throw of 13.5 m in 23 days has been fast pushed through successfully, ensuring yield stability of the dual inclined coalface during this period.

Study on the change law of disturbance principal stress and the stability of surrounding rock of vertical working intersection

ZHAO Weisheng，HAN Lijun，ZHANG Yidong

2015, 32(1): 90-98.

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Taking vertical working intersection in a mine as the background, the distribution law of disturbed principal stress vector (including the value and the deflection rule of the direction of such disturbed principal stress vector) of vertical working intersection, which keeps a different spatial location relationship with the in-situ stress, has been revealed through VB programming to dispose the data of numerical analysis. And the law of both the deformation and loose circle of intersection surrounding rock changing along the spatial location mentioned above has been studied by introducing the method of point safety factor. The result shows that such stress vector is mainly influenced by the in-situ stress but hardly by the spatial location and the excavation sequence of vertical working, and from the shallow of surrounding rock to the deep, the value of such stress vector decreases to in-situ stress after the first in crease; the maximum disturbed principal stress in the roof and floor of intersection is horizontal stress, while such stress in the two sides of intersection is vertical stress; the closer the axes in the vertical intersection is to the two horizontal principal stress normal bisector , the more stable the surrounding rock of intersection is. What is more, the surrounding rock is more stable when the roadway of intersection near the maximum horizontal principal stress is excavated firstly than the other excavation sequence.

Experimental research on the influence of blasting on the inclined crack in the back-blasting side of nearby roadway

GUO Dongming，LIU Kang，YANG Renshu，ZUO Jianping，FAN Jingchong

2015, 32(1): 99-104.

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Based on the often neglected problem of disturbance of explosive load to the defects of surrounding rock in adjacent tunnel back-blasting side, using explosion load digital laser dynamic caustics experimental system，the slant crack propagation regularities of neighboring roadway side are explored under explosion dynamic load. The experimental results show that crack extension final displacement is the largest, when the angle of prefabricated crack is in the side of back blasting of the straight wall and arch tunnel is 30° under the blasting load, then with the increasing or decreasing of crack angle, the ultimate displacements of crack extension all tend to decrease gradually; attenuated effect for stress wave of arc is less than the rectangle. Consequently, oblique upward crack extension displacement is 2-3 times of oblique down crack which is symmetry with horizontal subjected to blasting loading. In addition, energy release rate has driving effect on the propagation of the crack, and the energy release rate reaches the maximum in a moment and then gradually decreases to zero. But this change range becomes small with the crack extension displacement decreasing. The research provides theory basis for the economic and reasonable supporting of adjacent tunnel back-blasting side.

Study on the prediction of the vertical shaft freezing construction based on neural network model

WEI Jianjun，ZHANG Jie

2015, 32(1): 105-111.

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The premise and foundation of the scientific construction is to know the circle time and formation characteristics of the frozen wall under the different depths and lithologic strata in the process of vertical shaft freezing construction. In response to the existing objective problems of the vertical shaft freeze design, the reasonable input parameters as well as output parameters have been determined by using the neural network system theory. Based on the learning and training, the neural network prediction model of the vertical shaft freezing construction information has been set up. And then, the forming time and characteristic parameters such as inside and outside extended range, the average propagation velocity, effective thickness, the temperature of the wall, diameter range of the frozen rock-soil, average temperature have been predicted. Finally, the measured data and predicted data have been analyzed contrastively. The results show that, the measured results are consistent well with the predicted results. The prediction model has the advantages of the high prediction accuracy, wide applicability, which provides a theoretic foundation for the scientific design of the construction method and the supporting schemes during the course of the vertical shaft construction.

Experimental study on strength characteristics and deformation behavior of the cracked rock samples under uniaxial compression

NIU Shuangjian，JING Hongwen，YANG Dafang，GUO Jiaqi

2015, 32(1): 112-118.

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The prominent characteristic of the surrounding rock of tunnel is its capacity after it was broken. Correct evaluation of the strength characteristics and deformation behavior of the broken surrounding rock have an important significance on the surrounding rock stability control. In this paper, taking acquired cracked rock samples from the failure surrounding rock in km deep mine as the research object, according to the low even approximate to zero confining stress states of the broken surrounding rock, re-fracture tests of the cracked rock samples have been conducted by the MTS machine under uniaxial compression to study its strength characteristics and deformation behavior systematically. The results show that the fracture plane has obvious effect on the uniaxial compressive peak strength, but it has no direct and decisive influence on the residual strength; the stress-strain curves of cracked rock samples can be generally divided into two types, single peak and multi-peak; the fracture plane has no obvious effect on secant modulus，the Poisson’s ratios and peak axial strain, but it has obvious influence on peak hoop strain and volumetric strain; there is a close relation between the expansion process and failure mode of the fracture plane and angle of the main rupture surface—when the direction of loading direction is consistent with main rupture surface, failure mode is mainly vertical splitting, on the contrary, when the direction of the former is perpendicular to the latter, it is mainly vertical splitting holing through the main rupture surface, and combination of shear and splitting mainly occurs in other situations. The distribution of the fracture plane on surface of the cracked rock samples shows obvious fractal characteristics, and the uniaxial compressive peak strength is a linear monotone minus function to the Box Counting Dimension.

Research on the single freezing pipe temperature field under the condition of foam material partial insulation

ZHANG Tao，YANG Weihao，HAN Tao，HUANG Jiahui，ZHANG Chi

2015, 32(1): 119-125.

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Technology of partial insulation can solve challenging problems when freeze sinking method is applied into the deep shaft sinking project, and it can also save a large amount of cold energy. The partial insulation freezing temperature field of single pipe has been used as research object, in order to obtain the effect law of heat preservation material characteristics on the temperature field. Firstly, combined with the method of similarity theory and theoretical research, the dimensionless mathematical model and criterion of corresponding expression which attributed to the single pipe freezing temperature field have been derived. Secondly, combined with numerical calculation and simulation test, single pipe partial freezing problems have been studied under the condition of foam material freezing pipe, with the dimensionless criteria being used as influencing factors. The relationships between freezing-pipe dimensionless heat flux and specific heat，conductive coefficient，outer radius of insulating material have been obtained. The optimum selection range of conductive coefficient should be no greater than 0.035 (dimensionless), and the outer radius of insulating material should be at 1.4~1.6 (dimensionless). The conclusion can be widely applied to frozen engineering fields. It provides a theoretical foundation and convenient conditions for the design and application in the freeze sinking projects.

Research on deep jointed rock fragmentation by TBM cutters and cutters spacing optimization

SUN Jianzhong，YANG Shengqi，WEN Sen

2015, 32(1): 126-131.

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In order to optimize the layout of TBM cutters on deep jointed rock and improve the efficiency of TBM, two-dimensional discrete element software UDEC has been used to research the impact of joint spacing, angle and the cutter spacing on the rock fragmentation. The results show that when the joint spacing is 50 mm, cracks extend to the joint surface and spread along the tilt direction despite the barrier effect and the various angle of joints; when the joint spacing is not more than 100 mm, the rock cracks can extend to the joints but the crack propagations is controlled by the joints; when the joint spacing is no less than 150 mm, joints have no impact on the break rocks because the propagation of crack can’t reach the joints. When the spacing of horizontal joints is small, the joints will affect the rock fragmentation and the effects may gradually weaken until disappear with the increase of the joint spacing. The reducing joint spacing resulted in the best cutter spacing reduce when the small joint angle is 30° and the smaller joint spacing was better to break rock when the joint angle is 60°. The best penetration rises gradually with the joint angle increasing and increase more quickly from 2 mm to 7 mm when the joint angle increases from 0° to 90°.

Elastic-brittle-plastic mechanical model for rock with confining pressure

ZHANG Chunhui，XU Xiaopan，WANG Xizhao，ZHAO Quansheng

2015, 32(1): 132-137.

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To model effects of confining pressure on the post-peak mechanical properties for rock such as the degradation of strength and modulus, and dilatancy, the deformation process is simplified into three phases including linear-elastic, brittle degradation and perfect plasticity. Degradation index and dilatancy index are employed to reflect the effects of confining pressure on the peak-post mechanical properties for rock in this paper, and an elastic-brittle-plastic model with confining pressure is presented. Based on the transformation relationship between Hoek-Brown failure criterion and Mohr-Column failure criterion, how to obtain the calculation parameters of the peak-post mechanical model in this paper is presented. The Fish function method within FLAC is adopted to realize the elastic-brittle-plastic mechanical model model in this paper. In numerical case study the peak-post mechanical properties of rock under varied confining pressure including the degradation of strength and modulus, and dilatancy are modelled. The results show that the model can perfectly describe the deformation process and the effects of confining pressure on peak-post mechanical properties of rock．

Study on the monitoring method of three-dimensional stress with FBG in surrounding rock and the simulation experiment

WEI Shiming，MA Zhiyong，LI Baofu，CHAI Jing

2015, 32(1): 138-143.

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To achieve effective monitoring of three-dimensional stress state in surrounding rock and its change law with mining, the fiber Bragg grating (FBG) sensing has been used and the correlative simulation experiment has been carried out. The test structure sensitive to three-dimensional stress has been formed by respective pasting three fiber gratings parallel to x，y and z direction on the rubber matrix cube surface. Based on the generalized Hooke law, the mechanical relationship between the fiber’s strain and the rock’s stress has been derived, and the correlative mechanical calibration experiment has been performed. The result indicates that the sensor has a good mechanics response characteristics to three-dimensional stress, and the sensitivity coefficients of stress λ1 and λ2 are respectively 0.047 14 and 0.021 84 ε/MPa. In addition, the three-dimensional stress change in the simulation experiment during mining has been tested. The result indicates that the sensor can achieve the monitoring of three-dimensional stress in simulation models, and the result is consistent with the actual change process, and it can meet the requirement of rock three-dimensional stress detection.

Experimental study on permeability properties of coal seam under high pressure water injection

YU Yanbin，JIANG Yujing，CHENG Weimin，CHEN Lianjun，ZHOU Gang，WANG Gang

2015, 32(1): 144-149.

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For the purpose of studying the influences of permeability properties affected by the different pore-water pressures, MTS electro-hydraulic servo system has been utilized to conduct the permeability characteristics experiments of specimens from deep coal mine under the conditions of the different pore-water pressures, especially the high pore-water pressures. The results show that the permeability rate curves are quite consistent with volumetric strain curves, which are both U-shaped. Meanwhile, under a certain external condition, the effect of the pore-water pressures on the permeability properties and volumetric-strain depends on the critical threshold pore-water pressures of coal specimens. The permeability properties under higher pore-water pressure than the critical threshold have been improved several times than that under lower pore-water pressure. Moreover, the pore-water pressure has an important influence on ultimate strength of coal rock. The higher the pore-water pressure is, the lower the peak strength is. The more distinctive effects of dilatation emerge, the more strain is needed for the appearance of permeability peak. The research result provides the guidance for the employment of high pore-water pressure to improve the permeability and disaster prevention of coal seam water injection.

Experimental research on chemical grouting short hole shrinkage for weak-broken orebody

WU Aixiang，LIU Chao，HAN Bin，HUANG Mingqing，YU Shaofeng，WANG Heng

2015, 32(1): 150-155.

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The mining condition of deposit is extremely harsh in Tangdan Copper Mine, and the orebody and surrounding rock are loose, broken, unstable and have high mud content, so it causes a series of problems during mining such as difficulty of hole-forming and drawing, high dilution and loss rate and poor production capacity. Grouting technical scheme has been determined by the comparison of theoretical calculation and engineering analogy among different grouting schemes. The friable rocks will be bonded as a whole after the grout injected into orebody and part of hanging wall, and the mechanical property and integrity of the engineering rock mass, the hole-forming and mining index will all be improved. Through the comparison of 9 schemes based on mechanical calculation, lab experiments, and numerical simulation by using ANSYS and FLAC3D, the optimum design scheme in which the top pillars should be 15 m, the jams 16 m and the chamber 12 m has been concluded. The industrial experiment indicated that chemical grouting applied in short-hole shrinkage method can enhance ore's stability, improve the safety coefficient of stope, increase the fluidity of stored ores, decrease mining loss and dilution rate, which can realize the safety and efficiency mining of weak-broken ore.

Gas drainage radius and borehole distance along seam

LU Yi，SHEN Hongmin，QIN Botao，ZHANG Leilin，MA Hongfen，MAO Taoliang

2015, 32(1): 156-162.

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To determine the reasonable distance of gas drainage boreholes in coal seam being mined, based on the control equations of seepage and deformation fields, and the coupling equations of porosity and permeability, the solid and gas coupling mathematical model of gas seepage in drilling extraction was established. The drainage radius of gas extraction borehole in current coal seam was calculated by numerical simulation, and the relation between the borehole distance and extraction radius of single-borehole was deduced. Taking coalface 15107 of Huangyanhui coal mine for example, by the gas drainage experiments of single drilling and multiple drillings in this face, the correctness of the drainage radius, and the relation between borehole distance and extraction radius were calculated and verified. The research results provide a scientific basis for gas extraction.

Water coning effect in gas pressure determination of coal-rock mass containing moisture

LI Xiaowei，JIANG Chenglin

2015, 32(1): 163-167.

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The water coning of coal seam permeability coefficient and adsorption characteristic has seldom been studied at home and abroad. Aiming at that, the theory model of dynamical water coning breaking through boundary of drilling hole was established. The analysis presents that when evacuation during the process of gas pressure determination, gas flow amount is maximum, breaking through velocity of water coining is fastest, and the influence of gas flow decreasing after borehole sealing is smaller. Additionally, the relation between the time of breaking through boundary of drilling hole and the gas flow amount, thickness of coal seam, drilling depth and the porosity of coal mass in the rising process of dynamic water coning has been derived, and the times of water coning breaking through the boundaries with different flow rate, coal seam thickness and length of borehole were calculated. It is found that the breaking through time greatly reduces with the increase of flow rate. As the flow rate keep a constant, with the increase of the drilling depth, the breaking through time first undergoes a smaller variation process, and then decreases significantly. Moreover, using the ball direction flow field to determine the gas pressure in engineering , the influence of coal seam water coning to the gas pressure determination can be avoided by shorten the evacuation time.

Seepage rules of loaded coal containing gas under the coupling effect of temperature and axial deformation

WEI Jianping，WU Songgang，WANG Dengke，LI Furen

2015, 32(1): 168-174.

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Using the self-made triaxial seepage experimental device, an experiment was carried out under the condition of constant confining pressure, gas pressure and different temperatures, to simulate the gas seepage process of raw coal containing gas during the coal body deformation, and build the qualitative and quantitative relations between the permeability of loaded coal containing gas and temperature or axial strain. The results show that: 1) Axial strain has a great impact on loaded coal containing gas. Before the yield step of loaded coal containing gas, the permeability has decreased with the increment of axial strain, and the decreasing extent decreased gradually. After the unstable failure, loaded coal containing gas was broken suddenly, resulting in the permeability increasing severely to 769%. 2) Effect of temperature variation on permeability is closely associated with the stress-strain stage of coal containing gas. The experiment demonstrates that the influence of mining process on permeability of coal containing-gas can be divided into three main phases, that is, matrix expanding outward，matrix expanding inward, and slippage effect. 3) Calculation formula about the permeability of loaded coal containing gas was built suitable for the common effect of deformation and temperature, that is, k=(aT+b)εcT+d. This formula can well describe the relationship between the permeability of loaded coal containing gas and the deformation and temperature. The results can provide theoretical basis for the reveal of gas seepage law and mine gas prevention and control.

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