Journal of Mining and Safety Engineering

Intelligent expert system for designing bolt-grouting support of soft-rock roadways and its applications

WANG Lian-Guo, LU Yin-Long, SUN Xiao-Kang

2016, 33(1): 1-6.

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The bolt-grouting support design for soft rock roadway is a complicated non-linear problem which relates to many factors, such as hydrogeology, engineering geology, mining condition, rock mechanics, etc. To solve this problem, expert system technology in artificial intelligence field has been combined with theoretical research results and practical experience of soft rock roadway bolt-grouting support, due to which an intelligent expert system model for bolt-grouting support design of soft rock roadways has then been proposed. Based on the knowledge of soft rock roadway support engineering, the database of geomechanical properties of soft rock roadway, the database of project cases of soft rock roadway bolt-grouting support design and the database of expert experience knowledge of soft rock roadway bolt-grouting support design have been established. Furthermore, by using three kinds of reasoning strategies (theoretical calculation, BP-ANN and production rule), the core reasoning mechanism of the proposed expert system has been built to optimize the design of the parameters of bolt-grouting support for soft rock roadways. The proposed expert system has then been employed to design a soft rock roadway bolt-grouting support for a soft rock roadway in Huaibei coal mine area and the scientificity and reasonability of the selected parameters of bolt-grouting support for this roadway has been significantly improved. This system has also effectively maintained the stability of the soft rock roadway in the zone.

Support technology and device development of yield cables for the high stress and large deformation roadway

GAO Ming-Shi, YANG Qing-Song, ZHAO Yi-Chao, CHENG Zhi-Chao, QUAN Xiu-Cai

2016, 33(1): 7-11.

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Due to high stress and large deformation of deep roadway surrounding rock，the support system must have high-strength yielding characteristics. Deformation strength of yield device is equal to the limit of cable yield strength. So when the bearing capacity of cable goes up to or approaches the limit of yield strength, the yield device will respond firstly with yield strength reduction and displacement, and will release some energy, which makes it possible to avoid premature failure of over-load and keep surrounding rock of roadway long-term steady and to maintain its integrity. Simultaneously，the experiments to test mechanical property parameters of various yield devices have been done by using Rock Mechanics Test System MTS815. 3 types of yield devices for cables respectively match with cable support system in certain diameter (Φ15.24 mm，Φ17.8 mm，Φ18.9 mm) and strength. Engineering practice has shown that this support technology and success of new product development can protect the integrity of bolting mesh system effectively, and improve the quality and level of support for surround- ing rock of deep roadway.

Numerical analysis on percolation characteristics of water-enriched roof of roadway

YAO Qiang-Ling, CHEN Tian, LI Xue-Hua, LIU Kai, LIANG Shun, ZHU Chen-Guang

2016, 33(1): 12-18.

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Due to the excavation of roadway, the occurrence mode of water in the fractures of roof strata has changed, which has significantly decreased the strength of roof rock mass under the action of water and tends to induce large deformation of roof even loss of its stability. Field measurement on the occurrence position of roof effluent water and development law of surrounding rock internal fractures has been conducted in water-enriched roadway, and research has also been done on flow characteristics of roof water and variation law of pore water pressure as well as the influences of roof support intensity on the flow characteristics of roof water by means of numerical simulation under the following three conditions, no drain hole existing in the roof, drain hole existing in the roof and drain hole crossing the fissure-plane of roof strata, respectively. Research results have indicated that the occurrence position of roof effluent water locates in the developing area of fissures and it is conducive to drain roof water and control the stability of roof surrounding rock by reasonably arranging technical parameters of water drainage. Based on the above research, the technological principles of controllable water draining and reasonable water retention have been put forward and engineering application has also been conducted.

The mechanism of synergetic anchorage in deep roadway surrounding rock

LONG Jing-Kui

2016, 33(1): 19-26.

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In response to the difficulties during the surrounding rock control in deep roadway, based on previous research and engineering practices, the mechanism of synergetic anchorage in deep roadway surrounding rock has been put forward, taking synergetics as its theoretical basis and guideline. Through analyzing the components of the controlling system of the roadway surrounding rock, and introducing the way how synergetics direct the anchorage of surrounding rocks, a research framework has been built to propose the synergetic mechanisms concerning structure, intensity, rigidity, anchorage timing, preload, and deformation. The study shows that the synergetic anchorage system achieves the effect of 1+1>2, as its macroscale function outweighs the sum of its total subsystems. This is of fundamental and vital importance to the stability control of the deep roadway surrounding rock, and meets the essential needs of safety production of coal.

Numerical simulation research of bolt-grouting supporting mechanism in deep soft rock roadway

MENG Qing-Bin, HAN Li-Jun, QIAO Wei-Guo, LIN Deng-Ge, LI Hao

2016, 33(1): 27-34.

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Grouting test equipment for cracked rock mass has been developed independently, and grouting reinforcement test has been done on cracked rock mass. Mechanical characteristics and microstructure of cracked rock before and after grouting reinforcement have been explored. Concept of “equivalent layer of bolt-grouting reinforcement”has been proposed. Mechanism of bolt-grouting supporting in deep soft rock roadway has been studied with the method of FLAC3D. Influence of displacement and plastic zone under different thickness, elastic modulus, cohesion and internal friction angle of bolt-grouting reinforcement equivalent layer has been revealed. The paper has shown that as the parameter of the equivalent layer of bolt-grouting reinforcement improves, plastic zone and displacement of roadway surrounding rock have reduces, which has reflected that the grout can improve the integrity and strength of cracked rock mass. Research has laid a foundation for parameter optimization design of bolt-grouting supporting.

Influence of mining sequence of hanging wall and foot wall on mining-induced stress of fault coal pillar

DAI Jin, JIANG Jin-Quan

2016, 33(1): 35-41.

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The laws and differences of the load transmission of the basic roof over the gob area of the fault’s two sides have been studied under the condition of different mining sequence of hanging wall and foot wall, based on the articulated balance theory of the fracture rock mass, with the roadway being arranged along the boundary of the fault. And the characteristics of ground pressure of fault coal pillar and the mining gateway nearby have been studied with the method of field test. The study has shown that the load transmitting coefficient of fault is relatively higher, the hanging wall of coal pillar abutment pressure is low and that the foot wall coal pressure is relatively higher when the hanging wall of fault is firstly mined. However, the load of transmitting coefficient of fault is related with the angle of fault when the foot wall is firstly mined. When the angle of fault is larger, the load of the gob area overlying strata can be transmitted to the hanging wall, so the foot wall of coal pillar abutment pressure is low and the hanging wall coal pressure is higher; while the angle of fault is smaller, the load of the gob area overlying strata can hardly be transmitted to the hanging wall, so the foot wall of coal pillar pressure is higher and the hanging wall coal pressure is relatively lower. Therefore, different widths of the fault coal pillar should be considered according to different mining sequences.

Study on stability of strip coal pillar with different moisture content

YANG Yong-Jie, ZHAO Nan-Nan, MA De-Peng, ZHANG Fu-Jun

2016, 33(1): 42-48.

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The stability of strip coal pillar under high stress is obviously affected by water abundance of coal seam. In order to study the influence of moisture content on creep characteristics of strip coal pillar, creep tests of coal specimens with different moisture content have been carried out firstly, and the results have revealed that moisture content has obvious influence on creep characteristics of coal speci- mens, to be more specific, with the increase of moisture content, the creep deformation gets bigger, but the creep threshold value, the creep strength and the creep coefficient get lower. The fitting results of creep tests have shown that the creep mechanical properties of coal can be well described with the im- proved Burgers model. Based on the creep test results, the creep characteristics and stability of strip coal pillar with different moisture content have been analyzed with the FLAC3D numerical simulation soft- ware. With the increase of moisture content, the distance between the peak stress position and the strip coal pillar boundary will increase, so will the plastic zone of the strip coal pillar; meanwhile, the vertical stress of coal pillar and the creep deformation will decrease, but the bearing capacity of coal pillar will reduce, and the time the strip coal pillar using to gets into long-term stability state will in- crease. The simulated results have indicated that when the moisture content is 0.78%, 1.07% and 1.36%, the widths of plastic zone of the strip coal pillar are 10, 12 and 16 m respectively and the period the strip coal pillar gets into long-term stability is 18, 24 and 36 months respectively when other conditions remain unchanged.

Deformation mechanism and control of lower seam roadway of contiguous seams

YU YANG , SHEN Wen-Long, GAO JIE

2016, 33(1): 49-55.

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In order to solve the support problem of roadway locating in the lower seam of contiguous coal seams, this paper, taking Beiyu coalmine in Pu County, Shanxi Province as a case, has studied the stress field in the floor of gob belonging to upper seam and characteristics of deformation and instability for roadway locating in lower seam by means of numerical simulation. Principles of ground control for roadway roof in lower seam have been determined and different roof control methods have been tested in field. According to this research, three-dimensional combined roof control techniques based on hy- draulic expansion bolt and advancing insertion of tube on roof have been put forward with corre- sponding key parameters being determined through theoretical analysis and field test. Field test has suggested that control techniques raised in this paper are effective for the ground control of roadway in lower seam of contiguous coal seams and the general condition of roadway is good, which has provided great reference value for ground control of roadway in similar conditions.

Mechanical and deformation characteristics of gob-side entry retaining surrounding rock and support methods

JIANG Peng-Fei, ZHANG JIAN , HU BIN

2016, 33(1): 56-62.

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Taking the gob-side entry retaining at the working face 3311 at Hexi coal mine as the back- ground and using FLAC3D finite difference program, this paper has calculated and analyzed the distribu- tion characteristics of stress and deformation in the gob-side entry retaining surrounding rock, filled wall and coal pillars, and proposed reasonable support methods for the gob-side entry retaining. The research results have shown that: the fierce degree of the vertical stress and horizontal stress change in the immediate roof is obviously bigger than that in the main roof for the gob-side entry retaining; the mechanical change of the surrounding rock and filled wall is obviously influenced by the hysteresis mining-induced stress after the mining of the working face 3311 and the main impact is on the vertical stress change; at the second mining phase of the working face 3313, the deformation of the roadway surrounding rock caused by the mining influence at this phase is much more sensitive to the influence of the stress, which means after the action of the second mining stress, while the stress in the filled wall and the roadway surrounding rock increases moderately, the roadway deformation increases relatively significantly and is mainly in the form of convergence of floor heave and ribs. The underground test has indicated that with the combined support of the bolt, cable bolt and filled wall and optimized onsite construction, gob-side entry retaining has met the ventilation requirement of the mining face, reduced the cost of the roadway exaction and realized the rapid advancement of the mining face.

Numerical analysis of stability of roadway surrounding rock with weak interlayer under dynamic disturbance

TANG Li-Zhong, GAO Long-Hua, WANG Chun, JIANG Feng

2016, 33(1): 63-69.

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In order to study the influence of weak interlayer of different thickness a, position h and an- gle θ on the stability of surrounding rock of roadway under dynamic disturbance, numerical analysis of the mechanical response of roadway surrounding rock with weak interlayer under the action of stope blasting has been carried out using the finite element software ABAQUS, and the optimization support scheme has been put forward combing the practical conditions of roadway of Dongguashan Copper Mine. The results have shown that in conditions of dynamic disturbance：1) Both the stress and dis- placement have a non-linear relation with interlayer thickness a or position h upon the roof and two sides of roadway; the stability of the surrounding rock declines at first with the increase of a/h and then shows an up-going trend, which has indicated relative changes of the influence of a or h on secondary static stress of surrounding rock and dynamic disturbance attenuation. 2) With the increase of interlayer angle θ, the attenuation of the layer to dynamic wave rises up and then becomes more obvious when θ grows larger. 3) The weak interlayer as an important role on the stability of roadway surrounding rock of Dongguashan Copper Mine, support measures and technical parameters can effectively control the deformation of surrounding rock, which has verified above results.

Analysis and prediction of vertical shaft freezing pressure in deep alluvium based on RBF fuzzy neural network model

YAO Ya-Feng, CHENG Hua, RONG Chuan-Xin, LI Ming-Jing, CAI Hai-Bing, SONG Jian

2016, 33(1): 70-76.

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The field measurement of varied monitoring levels about the shaft freezing pressure in Dingji mine has shown that the freezing pressure changes with time and circumstance. It is easily influ- enced by many factors, such as strata depth, geotechnical moisture content, average freezing wall thick- ness and mean temperature, and that it has obvious uncertainty. The degree of uncertainty has been characterized by the variation coefficient, laying a foundation for optimizing the traditional RBF neural network and introducing variation coefficient of freezing pressure to fuzzy central value and weight value learning strategy to establish prediction model of shaft freezing pressure in deep alluvium. With variables of strata depth, geotechnical moisture content, average freezing wall thickness and mean tem- perature as the input information, the model has been used to distinguish clay strata and calcareous clay strata in training and learning with sample data from thirty three monitoring levels in seven shafts of Huainan and Huaibei areas, and finally has made an engineering prediction for the shaft freezing pres- sure in Kouzidong mine. The results have shown that the field measurement has well fitted with the pre- diction; the efficient and precise model algorithm has provided reliable basis for analysis and prediction of vertical shaft freezing pressure in deep alluvium of Huainan and Huaibei areas.

Study on the orthogonal numerical simulation experiment of the effect of surrounding rock mechanical parameters on roadway deformation and failure

QIN Zhong-Cheng, YU Xin, LI Qing-Hai, ZHANG Pei-Sen, HUANG Dong-Mei, WEN Zhi-Jie-

2016, 33(1): 77-82.

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This paper has presented a study on the effect of surrounding rock mechanical parameters on roadway deformation and failure with the method of orthogonal numerical simulation experiment. Re- searchers have selected 5 factors including internal friction angle, cohesion, Poisson’s ratio, tensile strength and Young’s modulus. The experiment results have shown that, according to the effect on roadway deformation, the sequence of these 5 factors is cohesion>tensile strength>Young’s modulus> internal friction angle>Poisson’s ratio; In terms of the importance to roadway failure, the order is cohe- sion>internal friction angle>Young’s modulus>Poisson’s ratio>tensile strength. This experiment results have well reflected the consequences of theoretical analysis, which has indicated that this method is highly effective for the study on the deformation and failure of roadways.

Study of rectifying shaft tower based on numerical simulation and Mindlin’s equation

ZENG Wei, MA Jin-Rong, WEN Kai, ZHU Kun-Peng, HE Ya, YANG Han

2016, 33(1): 83-87.

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The theoretical calculation and application based on the Mindlin’s Stress Equations have been widely used in Piled raft foundation, soil nailing wall, rock bolt foundation, etc., while rarely used in rectifying the tower, which has rigid connection with the shaft. Stress relief method has been suc- cessfully used in rectifying building but none in rectifying shaft tower. Numerical simulation and the Mindlin’s equations have both been utilized to verify that the stress relief method is effective in rectify- ing shaft tower. The results of Mindlin’s equations have been revised by considering the unloading ratio of the excavation, and they are in great accordance with the numerical simulation results. Both of them have shown that stress relief method can be successfully used in shaft tower rectification; and that in- creasing the width of the stress relief area, shortening the distance between stress relief hole and shaft tower, deepening the stress relief hole and increasing the diameter of the stress relief hole can effec- tively enhance the rectifying performance.

An analysis on strong strata behaviors and stress transfer of the roadway approaching gob in triangle area of the face end

YANG Jing-Xuan, LIU Chang-You, YU Bin, WU Feng-Feng

2016, 33(1): 88-95.

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There are obvious strata behaviors in the forepoling segment of No.5105 roadway approaching gob in the working face No.8105 in Tongxin coal mine in Datong mining area. The roadway deformation and single pillar breakage are serious, and the normal use of the roadway is affected seriously too. Based on the analysis of the characteristics of the strong strata appearing in the roadway ap- proaching gob, the main factor of the strong strata has been gained, and simultaneously the method of transferring bidirectional stress of the face roof to reduce the stress concentration in the triangle area of the face end has been proposed. The research shows that: the superposition of the bidirectional bearing pressure in the face end can bring out high stress concentration in the triangle area of the face end, which is the essential influence factor on the strong strata to the roadway forepoling segment; the three-parameter Weibull function in a changed form is adopted to analyze the superposition of the bidirectional support pressure, and the high stress magnitude and stress regional distribution in triangle area of the of face end is gained too; the technical measures of the stress transfer to reduce the stress distribution of the roadway approaching gob has been proposed. Field practice indicates that after using hydraulic fracturing technology to the roof of No.5105 roadway approaching gob and the return air roadway, the forepoling segment pressure of the No.5105 roadway has been significantly improved, and the amount of roadway deformation has been obviously reduced, ensuring the normal production of the coal face.

Study on field measurement and floor failure law of paste filling fully mechanized mining

CHANG Qing-Liang, TANG Wei-Jun, LI Xiu-Shan

2016, 33(1): 96-101.

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To solve the safety problem of coal mining above confined water, based on the engineering background of paste filling mining above confined water in Zhucun colliery of Henan Energy and Chemical Industry Group, using the theoretical calculation, numerical simulation analysis and field measurement method, failure laws of floor and evolution characteristics in paste filling mining have been studied , and prediction research of floor failure scope and water-inrush character of paste filling mining has been conducted, which has in the end revealed the mechanical mechanism of control floor failure in paste filling mining. Research has shown that the floor failure depth increases with the increase of mining height, but when added to a certain height (1.8 m), the floor failure depth tends to a relatively stable value; paste filling fully mechanized mining can make floor failure depth of about 12.0 m by the method of caving mining, reduce to about 2.0 m, and the water inrush coefficient reduce from 0.19-0.56 to 0.08-0.20. Actual measurement has shown that the maximum floor failure depth in full area of paste filling fully mechanized mining is about 4 m, and in area influenced by fault ranges from 10.0 m to 12.0 m. Water inrush disaster has not appeared in any process of paste filling fully mechanized mining, and the safety degree of mine extracting has been improved by lowering mining height and relatively increasing the thickness of water-resisting floor.

Mining affect of close distance coal seam to surrounding rock stress evolution of coal face in distressed zone

LIU Zeng-Hui, LOU Song, MENG Xiang-Rui, GAO Zhao-Ning

2016, 33(1): 102-108.

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To study stress evolution characteristics of surrounding rock in mining process of close dis- tance coal seams, according to the geological and mining conditions of 762 working face of No.8 coal seam and 962 working face of No.9 coal seam in Haizi coal mine, Huaibei mining group, three-dimensional numerical model was established to study the interaction of surrounding rock stress between the mining operation of 762 and 962 working faces. The results show that floor relief stress of 762 working face exhibits a nearly linear decrease, and forms relief zone in the headgate of 962 working face. The length shortening of 762 working face reduces the distressing effect to 962 working face, and the floor lateral concentration stress of 762 working face and the abutment pressure of 962 working face are superimposed. The pulse numbers of electromagnetic radiation monitored in gateways verifies the mining stress evolution of surrounding rock.

Mining-induced stress distribution and its evolution in fully mechanized top-coal caving face based on in-situ stress

LIU Qin-Jie, YANG KE , CHEN GUI , CHENG Rong-Fa, SHI Hou-Tao

2016, 33(1): 109-115.

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Value and orientation of in-situ stress play an important role in surrounding rock deformation, dynamic disaster and mining-induced stress field around the fully mechanized top-coal caving (FMTC) face, which was always little considered in the past related research work. The hollow inclusion strain gauge method was used to measure the in-situ stress in the south limb of Zhuxianzhuang(ZXZ) coal mine, and the original ground stress field has been feedback analyzed based on multi-objective constraints optimization method, while the results illustrate the optimum boundary loads and in-situ stress distribution. In addition, numerical models with FLAC3D have been established to investigate the influence law of mining-induced stress redistribution characteristics in FMTC mining face by the factors of the intersection angle between the longwall panel advancing direction and the maximum stress direction, the non-uniform coefficients of horizontal stress, and the lateral pressure coefficients, and so on. The results indicate that in-situ stress states has remarkable effect on mining-induced stress distribution and evolution characteristics of FMTC mining face. Finally, based on the real in-situ stress state, physical and mechanical parameters of coal-rock mass, and mining conditions of a coal face in ZXZ coal mine, the mine-induced stress distribution rules and its evolution process were further analyzed. Research results show that superposition and interaction of mining-induced stress and in-situ stress are important for strata management and roadway support in similar FMTC mining face.

The impact study on strata behavior laws of different coal seam spacing in ultra closed coal seams

WANG Xiao-Yi, SONG Xuan-Min, CHEN Chun-Hui

2016, 33(1): 116-121.

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In order to analyze the mining pressure behavior mechanism of lower coal seam working faces in shallow and closed coal seams while mining through upper coal seam goaf and left coal pillars, and determine the support resistance reasonably, the mine pressure change law and the support resistance of the lower coal seam in shallow and closed coal seams have been discussed. Results show that with the increase of coal seam spacing support resistance decreases. The mining pressure behavior will be influenced greatly by coal seam spacing when the coal seam spacing is less than 15 m while the influence will be very limited when the coal seam spacing is more than 15 m. The mining pressure behavior are different under the goaf, the left coal pillars and the coal seam：under the goaf the roof breakage pace is 9.8 m, the maximum operation resistance is 10 920 kN and the dynamic factor is 1.3; under the left coal pillars the roof breakage pace is 10.8 m, the maximum operation resistance is 11 065 kN and the dynamic factor is 1.35; under the coal seam the roof breakage pace is 12.2 m, the maximum operation resistance is 10 742 kN and the dynamic factor is 1.39.

Catastrophic analysis of support crushing disasters while roof cutting in shallow seam mining

YANG Deng-Feng, CHEN Zhong-Hui, HONG Qin-Feng, ZHANG Shan-Shan

2016, 33(1): 122-127.

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Aiming at the problem of roof cutting support crushing disasters caused by roof step convergence along the coal wall during the periodic weighting in shallow seam mining, based on the nonlinear variation characteristics during unstable failure of immediate roof under the abutment pressure, a system mechanics model composed by the main roof-immediate roof-powered support-waste rock was established. In addition, the instability mechanisms of the system under the loads were studied by catastrophic theory. The necessary sufficient condition for instability failure of the system and the formula of the jump value of displacement of immediate roof were gained, and the main factors for instability failure of the system were analyzed. The results show that the unstable failure of immediate roof leads to the roof cutting, the failure of the system is not only related to the stiffness ratio of the powered support, the immediate roof and the material parameters, but also related to the upper load and the cycle weighting interval. The rationality of the theoretical derivation has been verified by engineering example, some suggestions were given to the mining face.

Strength degradation and loading rate effect of sandstone containing a longitudinal fissure

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

2016, 33(1): 128-133.

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Fractured rock mechanics behavior is the foundation of underground engineering stability analysis. Experimental study on strength degradation and the loading rate effect of sandstone containing a lengthways fissure under uniaxial compression has been done based on the mechanics model of roadway roof in the western shallow buried strata. The results show that, split failure will dominantly happen in the samples when the translation distance is small (0-6 mm); while mixed failure of split and shearing will probably occur when the translation distance is large (12-24 mm); and the shearing failure is the decisive factor leading to final instability. With the increasing of fissure translation distance, sample capacity presents a trend of increasing first, then decreasing and gradual increasing again, and the translation distance between 6 mm to 12 mm appears an obvious sudden change region which is closely related to the failure form of the samples. The capacity of sample containing lengthways fissure increases gradually with the increasing of loading rate, however the strength degradation coefficient decreases and presents the staged characteristic of first sharp decline and then gentle variation.

Ecological significance and method to design protective coal pillar on surface runoff in desert shoal area

LI Tao, WANG Su-Jian, LI Wen-Ping, CHEN Tong, GAO Ying

2016, 33(1): 134-139.

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It is significant for the mining watershed ecology to design protective coal pillar on surface runoff in ecologically fragile mining area. Taking Shennan mining area in Northern Shaanxi Province as research area, ecological carrying characteristics of watershed in desert shoal mining area have been investigated with methods of field geological investigations and sampling tests. Based on the research of development rules of water flowing fractured zone, limitations of traditional design for protective coal pillar have been analyzed. And a new method to design protective coal pillar, on the basis of watershed mining, has been proposed from the point of hydrodynamics of groundwater. The results have shown that on one hand surface runoff satisfies the most gross of ecological water requirement, as well as domestic and production water demand, but on the other hand 91.33% of surface runoff comes from ground water recharge in the sand layer. The water flowing fractured zone heights will reach 40.4 m to 69.2 m as first coal seam’s mining around drainage basins, and at the same time, sandy aquifer above goaf will drain off after mining. The new designing method based on watershed can avoid reverseseepage of surface runoff into goaf. The practical calculation has shown that the designed protective coal pillar is 62 m around Changjiagou River based on watershed, which is greater than 34.8 m of the traditional design for protective coal pillar.

Draining test of mine water inrush under complex geological conditions and its hydrogeological significance

QI Yue-Ming, LI Min-Zu, XU Jin-Peng

2016, 33(1): 140-145.

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In order to avoid lacking of awareness and usage of the process of water inrush, drainage test of mining water inrush on site were studied under complex geological condition on the base of a comprehensive analysis of the background field near the water inrush point and risk assessments. Re- sults show that the process of mine inrush water under certain conditions can be successfully used as drainage test, and some following roles can be gained such as determining the water source, revealing hydrodynamic process, calculating hydrogeological parameters, and revealing the Karst medium condi- tions and reasons for water inrush, and so on. The new method has been carried out to get access to hy- drogeological information which was difficult to get using routine methods, providing important scien- tific data for analyzing water inrush reasons, and dealing with efficiently water inrush disaster.

The boundary conditions of model test for deep engineering and its simulation methods

FAN Peng-Xian, WANG Ming-Yang, FANG Xiang

2016, 33(1): 146-151.

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Along with the increasing of buried depth of underground engineering, the boundary condition of geomechanical model test has become one of the most important problems restricting the scientificity of simulation test in deep rock mass. The flexible uniform pressure loading technique has made it possible to equally distribute the boundary stress. However, the boundary condition can still not be met strictly. In this paper, the stress and displacement of surrounding rock mass of real excavation have been analyzed based on elastic-plastic theory. The main source of error in simulating deep rock store environment under the existing loading conditions and the reason why the deep environmental simulation can not be accepted have been revealed. Loading method by using a combination of springs as an equivalent action of peripheral rock mass has been presented to simulate boundary conditions. And the formula of equivalent springs stiffness of loading plate has been deduced by the equivalence of the displacement and stress, and both the advantages and disadvantages of this method have been discussed.

Parameter sensitivity analysis of temperature field in single fracture rock mass based on Morris

LIU Bo, JIN Ai-Bing, GAO Yong-Tao, DENG Fu-Gen

2016, 33(1): 152-157.

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Based on the three-dimensional discrete element numerical simulation (3DEC), the model of flow and heat transfer in single fracture rock mass has been established. Furthermore，combined with global sensitivity analysis method of Morris, the“elementary effect”of each parameter has been calculated by the value variation of one parameter in turn. In addition, the mean value μ and variance σ have also been obtained. Moreover, according to the value of μ and σ，the effect of each parameter on model temperature output and the law of the spatial and temporal distribution of μ and σ have been analyzed. Research results have shown that：slit aperture (b), fluid-rock heat transfer coefficient (h)，rock Thermal conductivity (KT ), rock mass specific heat (Cs), and fluid specific heat (Cf) have an important impact on the temperature output of the model, what is more, rock thermal conductivity (KT ), rock mass specific heat (Cs), and slit aperture (b) have a great interaction with other parameters. With the increasing of time step, μ and σ could be basically divided into 3 stages: rapidly increasing stage, slowly increasing stage and stable stage. Furthermore, along with the direction of fracture fluid flow and crack normal, the value of μ and σ has presented a decreasing tendency. More interestingly, compared with the negative influence of b and Cf on the temperature value, Cs has presented a positive effect. However, for the different positions of h, u and KT , those parameters have both positive and negative effects.

Numerical simulation of SHPB tests for coal by using HJC model

LI Cheng-Wu, WANG Jin-Gui, JIE Bei-Jing, SUN Ying-Feng

2016, 33(1): 158-164.

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By using the Holmquist-Johnson-Cook (HJC), the constitutive model, the Φ50 mm split Hopkinson pressure bar (SHPB) tests for coal have been numerically simulated with the finite element analysis software LS-DYNA. The simulation results have reoccurred the stress waves shape, stress variation and the destruction process of coal specimen during the SHPB tests. By contrast, it has been found that the numerical simulation is similar to the experiment results, and that the dynamic destruction process of coal specimen during the SHPB tests can be reoccurred reasonably with HJC constitutive model. The numerical simulation has shown that：1) The coal specimens have been destroyed firstly from around with the destruction mode of splitting failure in the axial direction mainly. 2) When the impact velocity is about 3 m/s, the destruction of the coal is caused by both compression and tensile; When impact velocity is about 9 m/s, the destruction of the coal is caused mainly by compression. 3) The destruction of the coal is out of sync with the peak stress: when the dynamic load is lower, the destruction of coal specimens lags behind the stress peak; when the dynamic load is higher, the destruction of coal specimens is ahead of the stress peak.

Engineering application and experimental study of parallel boreholes sleeve fracturing method for stress measurement

RONG Chuan-Xin, PENG Shi-Long, CHENG Hua, LI Ming-Jing, CHENG Shuai, YUAN Xiao-Yong-

2016, 33(1): 165-171.

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In view of limitations of the sleeve fracturing method for deep in-situ stress testing, a sleeve expansion pipe was improved for ground stress measurement. Synthesizing the characteristics of single-hole sleeve fracturing method and control fracturing method, a more operable ground stress measurement technology of parallel boreholes sleeve fracturing method was provided in this paper. Additionally, the formulas for the single-hole sleeve fracturing and the control fracturing were modified reasonably through the testing. The results show that the correction coefficients obtained for single-hole sleeve fracturing method was 0.78, while that for control fracturing method was 0.83. In-situ test was carried out for main track roadway buried in 965 m underground located at Zhuji east coal mine. The test results show that the maximum principal stress is 23.16 MPa in the west-east direction, the intermediate principal stress is 21.04 MPa in the vertical direction, and the minimum principal stress is 13.01 MPa in the north-south direction.

Occurrence mechanism and time-dependency effect of buckling rock burst

WENG Lei, LI Xi-Bing, ZHOU Zi-Long, LIU Ke-Wei

2016, 33(1): 172-178.

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To analyze the formation mechanism of slabbing thin plate in surrounding rock and the mechanical mechanism of bulking rock burst, the differentiation law of principle stresses during the deep roadway excavation was studied by numerical simulation. Based on three-parameter viscoelasticity constitutive relationship and the slabbing thin plate mechanical model for buckling rock burst, the buckling time-dependency equation of buckling rock burst under two dimensional stress state was theoretically derived, and the time-dependency features of bulking rock burst under different stress states were discussed. Simulated results indicate that for the roadway where vertical geo-stress is greater than horizontal geo-stress, the principle stresses decrease and the rock energy releases gradually in the roof and floor with the excavation process, while the principle stresses in sidewalls appear to be largely different, the tangential stress increases while the axial stress decreases in sidewalls where the rock mass energy accumulates massively. On the contrary, for the roadway where horizontal geo-stress is greater than vertical geo-stress, the differentiation evolution process of stresses and the characteristics of energy accumulationare the opposite. The results illustrate the mechanism of delayed rock burst, that is, when the slabbing thin plate structure in surrounding rock forms, the thin plate starts to bend and creep under the action of two-dimensional stress state, after the deformations reach to a limited value in a period of time, the slabbing thin plate structure will bulking fail and release massive elastic strain energy simultaneously.

Frequency characteristics of acoustic emission signal during rupture process of siltstone based on HHT

ZHANG Yan-Bo, LIANG Peng, SUN Lin, LIU Xiang-Xin

2016, 33(1): 179-184.

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By the uniaxial compression tests of siltstone samples, frequency characteristics of acoustic emission (AE) signals in the failure process of siltstone rock were investigated based on HHT analysis. The results show that HHT is a kind of signal time-frequency analysis method based on principal component analysis, which can determine the major and minor components of the signals, and precisely describe the time-frequency characteristics of the signal with instantaneous frequency. The time-frequency distribution of AE signal of siltstone can be divided into three stages during rupture process: initial zone, wave zone, and quiet zone. Main frequencies of AE signals during rupture process of siltstone samples are associated with stress levels, that is, main frequency decreases with the increase of stress level be- fore siltstone failure. From the stable extension of crack to unstable extension, until the rock failure, high energy AE signals transfer from high frequency to low frequency, and its duration increases. Appropriate monitoring bands of AE signals during siltstone rupture process is 20-120 kHz.

Research of the disturbance of curved roof caving for gas in upper corner

FU Ming-Ming, ZHANG Ying-Hua, HUANG Zhi-An, GAO Yu-Kun, FENG Cai-Yun, XIAO Shan-Lin

2016, 33(1): 185-190.

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By the means of force equilibrium analysis of the arc roof, four major factors affecting its balance have been identified. The four key factors have been used in the simplification of irregular triangular body model. And the formula for calculating volume change during the roof caving has been derived, which has indicated that if the sum of the volume change during roof caving, volume change of work surface interior and the lower corner during weighting process substracts the air leakage into goaf, the incremental value of emission gas from the upper corner position during the weighting process can be calculated. By analyzing the upper corner CH4 volume fraction monitoring records of four mine working face, the change rule of upper corner gas volume fraction during the weighting process has been concluded, which has shown that the upper corner gas emission is influenced by the upper arc roof. With periodic roof caving, emission of upper corner gas has significantly increased periodically. According to the air monitoring data near upper corner of Kangcheng and Yunjialing coal mine, the increased air volume of upper corner during the weighting process has been conducted. Based on the comparison between the measured data and theory calculation, the error is less than 5%.

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