Table of Content

15 January 2014, Volume 31 Issue 1

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Experimental study on short columns under axial load of U-type confined concrete arch centering and its application in mine

LI Wei-teng, WANG Qi, WANG De-chao, LI Shu-cai, HUANG Fu-chang, WANG Hong-tao, ZHANG Hong-jun, SHAO Xing

2014, 31(1):  1-9. 

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In order to clarify the basic mechanical properties of the latest invented U-type confined concrete arch centering, the axial compression experiment program of U-type confined concrete (UCC) short columns is designed. And from the aspect of deformation and failure modes, load-strain curves, ultimate bearing capacity, core concrete response characteristics of the acoustic emission and so on, the mechanical behavior, deformation and failure character are analyzed, and the fracture mechanism of core concrete is researched. The study result shows that the failure modes of UCC short columns under the axial compression is in overall plastic instability, and the N-ε curve shows the rise → gently rise 4 stage type. UCC short columns have better ductility and post-bearing capacity, with the ultimate beating capacity increasing by 127%~196%. Accordingly, the economy improves. Acoustic emission activity shows 4 periods: incubation → active → stabilization → elimination death. At the same time the deformation & failure behavior and mechanism of UCC short column are obtained by comprehensive analysis. The application effect shows that UCC arch centering is a new effective support for deep and soft rock roadway, and the surrounding rock controlling effect is much better than U-steel arch centering.

Rational width of narrow coal pillar based on the fracture line location of key rock B in main roof

WANG Hong-sheng, ZHANG Dong-sheng, LI Shu-gang, WANG Lin, WU Lin-zi

2014, 31(1):  10-16. 

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In this paper, to master the influence law of the main roof’s fracture structure on the stability of narrow coal pillar, the mechanical model of surrounding rock structure in gob-side entry was built, three fracture forms of the overlying main roof in gob-side entry were put forward, and the correlation between the fracture structure of main roof and the stability of narrow coal pillar was analyzed. The results show that there are great differences in the stress of roadway surrounding rock, and the stress and strain in coal pillar while the fracture line of main roof locates in different places. When the fracture line of main roof locates just at the top of the roadway, the surrounding rock deformation closed to the goaf is larger than that closed to the entity coal wall. The stress in the roadway roof is reduced fast, the surrounding rock is crushed and its anchoring ability is pool. The stress and deformation in pillar are increased fast, and the loads on the pillar are the largest when the surrounding rock is stable. Meanwhile, the continuous deformation speed of coal pillar is also the largest, which leads to the difficult later maintenance of roadway. When the fracture line of main roof locates in the lateral of roadway, the pillar deformation is in a reasonable scope, and the supporting capacity is strong, which is beneficial to the maintenance of roadway. The research results have been applied successfully in the No.8105 fully mechanized face with sub-level caving of Yanjiahe Coal Mine, and satisfactory technical and economic effects are achieved.

Study on supporting failure mechanism and reasonable length of anchor cable in thick soft-weak roof of high-stress coal roadway

WANG Wei-jun, LUO Li-qiang, HUANG Wen-zhong, QU Yan-si, WU Hai, YU Wei-jian

2014, 31(1):  17-21. 

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With the traditional method, large-area supporting failure often arises in anchor cable which causes the result that the maintenance of roadway is very difficult and the cost is high in thick soft-weak roof of deep coal roadway. Through field investigation and theoretical analysis, the factors of anchor cable supporting failure have been studied. The study indicates that the main reasons of anchor cable supporting failure are deformation of cable holes during constructive process in thick soft immediate roof and anchor agent damage during installation. Accordingly, the new design method of anchor cable parameters applying to thick soft immediate roof is proposed. The results show that the length of anchor cable in accordance with the new method is shortened and the anchoring force is improved greatly, and therefore the maintenance of roadway is improved significantly.

Arrangement and support technology of open-off cut along gob area in fully mechanized caving face

JIANG Li-shuai, MA Nian-jie, ZHAO Zhi-qiang, JIA Hou-sheng

2014, 31(1):  22-27. 

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Open-off cut along gob area of fully mechanized caving face has the characteristics of large span, large thickness of top coal, small coal pillar along gob area, soft surrounding rock and fracture development, so, its support is difficult. In this paper, in view of the open-off cut along gob area with 8 m in width, and 5.6 m in thickness, by using theoretical analysis, numerical simulation, field test and monitoring analysis, the remaining principle of coal pillars and pillar stress distribution characteristics were studied, and the coal pillar width was optimized. In addition, the support mechanism of open-off cut along gob area was analyzed, and the supporting schemes including the anchor net belt combined with anchor cable, and the anchor net belt with truss and anchor rope were designed and tested. The results show that the rational width of coal pillar is around 4~5 m, and the two supporting schemes of anchor net belt combined with anchor cable and truss and anchor rope, respectively, can improve the forced state of top coal and the bearing capacity of surrounding rock, effectively control the bed separation, fracture propagation, bending and subsidence of large span and thick top coal, and ensure the stability of open-off cut along gob area of fully mechanized caving face.

Study on the asymmetric deformation mechanism and control countermeasures of deep layers roadway

WANG Jiong, GUO Zhi-biao, CAI Feng, HAO Yu-xi, LIU Xin

2014, 31(1):  28-33. 

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The paper presents the research results based on failure mechanism and control countermeasures by numerical analysis and engineering tests. It shows that with the increase of buried depth, ground stress, and especially the influence of the horizontal tectonic stress, the surrounding rock of tunnels performs large asymmetric deformation under the original supporting conditions, and the key parts of failure are at the cross section of roadway layer and rock tendency layer; dislocation deformations such as shearing slip deformation between different layers and extrusion deformation of soft rocks by the influence of asymmetry structure of surrounding rocks will also occur. Combined with field engineering geological conditions, the asymmetric coupling support countermeasures by using bolt-mesh- anchor and anchor in corner to strengthen key parts supports are put forward, which shows good effect in field applications on asymmetric deformation and dislocation deformation controlling, and surrounding rock stabilities are improved.

Study on supporting technology for roadways of soft rock mass in natural caving method

MING Jian, SHAN Qiang, YAN Rong-fu

2014, 31(1):  34-40. 

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As for the problem of intense roadway layout, long time existence, large mining influence and great maintenance difficulty in the mine with natural caving mining method, a comprehensive method including field investigation，laboratory test，theoretical analysis, underground roadway test and deformation measurement has been used to analyze the deformation failure characteristics and support difficulties. With the guidance of confining pressure restored reinforcement theory, the active and passive combined support system of the surrounding rock is put forward, and mudsill, roof-contacted filling and other enhanced support techniques are adopted. The industrial test shows that the roadway deformation can be controlled within 80 mm after support provided. This proposes support technology can effectively control the surround rock deformation in soft rock roadway, which ensures the safety and feasibility of natural caving method in soft rock.

Space breeding mechanism of rock burst and its microseismic characteristics

WANG Gui-feng, DOU Lin-ming, LI Zhen-lei, GONG Si-yuan, HE Jiang, CAI Wu

2014, 31(1):  41-48. 

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Based on variation characteristics of “surrounding rock-coal” system during coal mining, a space breeding model of stope was established in this paper. In the model, roof, coal seam and floor was regarded as a whole system to investigate the fracture, instability and burst process of coal-rock structure. In addition, this theory was verified through microseismic monitoring in a stope with strong rock burst tendentiousness.The results show that the space breeding model can accurately describe the entire process from stable state to instability of coal-rock structure. The area with high static stress concentration is the stress basis for instability and failure of coal-rock structure. Mining operations launch the dynamic process of strong tremor and rock burst, and the dynamic load caused by roof fracture can quickly trigger the dynamic process into crack mutation stage and even lead to instability and failure of coal-rock structure. The emergence of strong tremor and rock burst depends on whether the high stress concentration area can reach high inoculation degree before it was unloaded and destroyed gradually. Crack extension stage shows the abnormal precursory information of strong tremor and rock burst, and the crack mutation stage predicts the occurrence of strong tremor and rock burst. The previous strong tremors and rock bursts in No.2 Workface of No.1-3 District show obvious breeding characteristics. Especially before the rock bursts happened on 26th, Jun and 15th, Oct, the seismic events and energies are very active, which presents a more obvious breeding characteristics.

Study on the deformation and fracture feature of steep inclined coal seam roof based on the theory of thin plates

TU Hong-sheng, TU Shi-hao, CHEN Fang, WANG Chen, FENG Yu-feng

2014, 31(1):  49-54. 

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Based on the geological occurrence conditions of roof and floor steep coal working face and the characteristics of middle and lower caving gangue filling of goaf, the force model of steep coal working face is established by using theory of elastic thin plate, flexure deformation characteristics under overlying strata and inferior goaf filling gangue are studied, and the theoretical calculation formula of goaf filling width and deflection equation of roof deformation is obtained. In light of the field parameter at Xintie mine of Long Mine group in Qitaihe branch, the study have shown that in the steep inclined working face, there is a larger deformation in the roof in the upper part and less deformation in the lower part; maximum deflection is 24 m away from working face end, with maximum deformation 320 mm; In the working surface of coal wall in the front and rear upper coal wall, roof and upper part of caving rock contact office will first appear to stretch or cause shear failure, finally will form an “U”type breaking. Research results conform to actual roof deformation.

Research on the application of continuous miner shortwall mining technology in gently inclined longwall face

ZHOU Mao-pu, CAO Sheng-gen, JIANG Xiao-Jun

2014, 31(1):  55-59. 

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To solve the problems in the operation of continuous miners in mining caused by bigger-angled gently inclined coal seam, this paper proposes such strategies as adjustment on apparent dip in roadway arrangement, choice of crawler type continuous transport system, and adjustment in feeding patterns of the continuous miner, which can insure the operation of the continuous miner and its post-support equipment in reasonable angles, minimize the amount of triangle residual coal, and realize the safe and high efficient mining in gently inclined coal seams with the continuous miner. The application of these above-mentioned strategies in real practice in Dongpo Coalmine brings satisfactory results: 1) Mining in gently inclined coal seams with continuous miners has achieved monthly advance of 550 meters per single entry on average; 2) monthly extraction of coal has reached 55 000 tons averagely. This offers valuable reference for the application of continuous miners in gently inclined coal seams in China.

Distribution and variation of mining-induced stress field in deep workface

LIU Jie, WANG EN-yuan, ZHAO EN-lai, XU Wen-quan, HU Shao-bin

2014, 31(1):  60-65. 

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To prevent the occurrence of dynamic disaster in deep soft coal seam, based on the engineering background in No.2 Coal Mine of Pingdingshan Tianan Coal Co. Ltd., the mining-induced stress field in the deep workface was measured by using the stress real-time monitoring system, and the distribution and variation of stress along strike and inclination was studied. In addition, the effect of stress on coal stability and dynamic phenomena was further analyzed, and the dynamic disasters which may occur in this workface were discussed. The results show that in the upper part of workface, which is approaching the gob-side, the influencing distance of advanced mining-induced stress, the stress concentration range within the roadway coal sidewalls are larger, and the stress concentration factor and peak value of stress are higher. The stress distribution and variation is quite different between the head and end of the workface. Moreover, the variation of peak stress and stress gradient significantly influence the stability of coalmass. Because the main disaster probably occurred at the workface is extrusion disaster controlled by the stress, the dynamic disasters can be fore casted by monitoring the stress changes at the workface.

Analysis of large-span goaf roof instability critical parameters and stability

ZHANG Hai-bo, SONG Wei-dong, FU Jian-xin

2014, 31(1):  66-71. 

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For the comprehensive analysis of complex goaf roof stability, the method combining classical mechanics and numerical simulation is adopted. With simply supported beam theory, load transfer intersection line theory, and ratio of span and thickness equation, the goaf roof instability critical parameters are theoretically calculated. The FLAC3D numerical simulation software is utilized to give a study of the surrounding rock stability. Results indicate that the goaf is instable when the roof structure parameters are all higher than the instability critical parameters; according to the goaf roof stability numerical simulation analysis, the roof central displacements are larger than the pillar lateral displacements with a maximum of 4.7 cm；the goaf roof minimum principle stress is near to the tensile stress; plastic zones are distributed to varying degrees in the goaf roof, floor and pillars, especially widely distributed in the pillars, showing that the goaf surrounding rock is in poor stability and the goaf is obviously instable. Reasonable measures should be taken in time to deal with the goafs. As it shows, the numerical simulation with FLAC3D, which can comprehensively evaluate the instability factors of the goaf, and truly reflect the state of goaf surrounding rock stress-strain and plastic distribution, has widespread applicability.

Water migration in arid mining area and thought of“water preserved mining”

CHANG Jin-yuan, LI Wen-ping, LI Tao, QIAO Wei, WU Fa-quan

2014, 31(1):  72-77. 

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Large-scale mining has produced great influence on local fragile eco-environment in Northern Shaanxi, such as leakage of aquifer and reduction of flows. Under this background, to acquire the migration situations of water resources in arid mining area, taking Shennan Mining Area in Northern Shaanxi as example, a series of works were carried out to study the division evaluation of water resources’ leakage degree, water resources quantity forecasting after mining, and analysis and comparison of water quality in goaf. The results show that the gross quantity of water resources in the mining area increases after mining, and the water in goaf is the main source of the growth. Consequently, the gross amount of water resources is proposed as the evaluation standard of “water preserved mining”. If the gross amount of water resources before mining is greater than that after mining, the water resources are running off on the whole. On the contrary, it is considered that the mining process can improve the oc- cur rence condition of water resources in some specified region, that is, the coal mining is beneficial to water resources protection. From above standard, water resources environment in Shennan Mining Area is improved.

The determination method of elastic modulus of deep damage rock mass

JIN Chang-yu, LI Jie, FENG Xia-ting, SUN Cheng-shuai, LIU Jian-po, XU Shuai, YANG Cheng-xiang

2014, 31(1):  78-83. 

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Excavation in deep underground cavity results in numerous micro-cracks on the surface of surrounding rock. In the readjusting process of stress field, propagation and coalescence of these cracks will cause severe problems such as spalling, board split and collapse, which make it difficult to determine the elastic modulus in the damaged zones using drilling method. In this paper, based on the damage mechanics principle, the general range of the elastic modulus in the damaged zones is preliminary judged by in-situ sonic test combined with empirical formula, and then the distributing regularity of elastic modulus in damaged zones is obtained by accurate inversion using neutral network and RDM model. This approach is applied in the 27th stope of Hongtoushan Mine and it has been proved to be valid and feasible to determine both the elastic modulus of damaged rock mass and distribution regularity of rock mass integrity in deep underground projects.

Analysis on development characteristics of Karst collapse column and water inrush risk in Shuangliu coal mine

LI Zhen-hua, LI Jian-bo, HE Zhi-hong

2014, 31(1):  84-89. 

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In order to prevent Karst collapse column conducting ordovician limestone water and making great mine flood, the basic characteristics of Karst collapse column in Shuangliu coal mine are studied by geometric parameters, development characteristics, precursory and distribution characteristics through theoretical analysis and field observation. It indicates that Karst collapse column mainly develops in shallow parts with small faults, while the attitude of coal and rocks is mainly distributed within ordovician limestone Karst dissolution pore and cave development region. Taking X15 Karst collapse column from 220 working face in Shuangliu coal mine as an example, the water inrush risk is analyzed by FLAC3D during mining upper coal group when there is Karst collapse column. The results show that: with working face moving forward, plastic failure fields, stress and seepage field of surrounding Karst collapse column begin to change. When the face moves to 30 m from the Karst collapse column, the plastic failure fields and seepage field begin to contact with each other, and with the face advancing, it extends to heavy water inrush risk.

Restrictive function of lithology and its composite structure on deformation and failure depth of mining coal seam floor

ZHU Shu-yun, CAO Ding-tao, ZHOU Hai-yang, YANG Chao-wei, LIU Jin-guo

2014, 31(1):  90-96. 

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In order to study the relationship between lithology and its composite structure and deformation and failure depth, based on these comprehensive field test data, restricting function of deformation and failure depth to mining coal seam floor by lithology and its composite structure is discussed. The obvious difference characteristics are obtained on homogeneous floor and soft and hard rock composite structure floor. The study results show as follows：1) The law of deformation and failure of homogeneous floor is relatively simple; the depth of deformation and failure of mining floor is controlled by the strength of floor, and has a gradual characteristics from strong to weak below floor on the whole；2) The deformation and failure floor of soft and hard rock composite structure is complex. There is an obvious restrictive function to the depth of failure floor and deformation degree by the composite structure, weak intercalation being the main weak surface which has strong constraint effect to the depth of failure floor. Namely, soft rock plays an important the effect of the cushion for overlying hard rock, and can produce stress diffusion effect for underlying hard rock. The results show that the floor of lithology and its composite structure has an important restrictive function on the deformation and failure of mining floor depth, and also has theoretical and practical significance to supporting tunnel and preventing water-inrush from mining floor.

Experimental study on coal face direct passing collapse column by hydrochloric acid softening method

ZHAO Guo-fei, KANG Tian-he, YANG Yong-kang, GUO Jun-qing, ZHANG Wen-yang

2014, 31(1):  97-101. 

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In order to solve the problem of coal face direct passing collapse column, hydrochloric acid softening method of coal face direct passing collapse column is proposed and carried out successfully. Through the methods of laboratory immersion test, rock mechanical characteristics test, X-ray diffraction and so on, the change law of rock sample in different concentrations hydrochloric acid, soaking time and its softening mechanism are studied. The study results show as follows: 1) The mechanical strength of sandy mudstone is negative logarithmic law changes with soak time of hydrochloric acid solution; 2) The exponential law of the mechanical strength of sandy mudstone decreases with hydrochloric acid solution concentration increasing; 3) With hydrochloric acid solution concentration increasing, its porosity increase, yield point is obvious and plastic to raise, but its elastic modulus changes insignificantly; 4) The decrease in the contents of muscovite and kaolinite mainly lead to the decreased mechanical strength of sandy mudstone; 5) Suitable hydrochloric acid solution concentration, soak time, the amount of injecting liquid and the cutting depth of the shearer can make sure of coal face’s normal advancement. Practical application shows that this safe, reliable, efficient method can provide references for coal face direct passing collapse column under similar conditions.

Study on the dynamic height of caved zone based on porosity

XIA Xiao-gang, HUANG Qing-xiang

2014, 31(1):  102-107. 

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Based on the formation process of caved zone, the dynamic height of caved zone is studied systematically. The studies have shown that the ultimate caving height mainly depends on residual broken expansion coefficient of breaking down rock dispersions, while the residual broken expansion coefficient is determined by the porosity of breaking down rock dispersions. Accordingly, the porosity calculation model is set up by fractal geometry. The relationship between residual broken expansion coefficient and initial broken expansion coefficient of rock is given based on the porosity calculation model. The calculation model of ultimate caved zone height of caving rock filling the whole mined-out area is deduced. At last, the model is verified by an engineering example.

Features of overburden failure and water filling in coal mining with sub-level caving under Santaizi reservoir

FENG Guo-cai, XU Bai-shan, WANG Dong

2014, 31(1):  108-114. 

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To solve the security problem of fully mechanized mining with sub-level caving in the super-thick coal seam under the reservoir, by the flushing fluid leakage measurement in surface borehole and detection of EH-4 continuous conductivity profile instrument, the overburden failure features and water filling states before and after N1S1 Coal Face mining in Daping Coal Mine were detected, and the deformation and failure features of overburden were retrieved and simulated by using RFPA2D Software. The results show that the permeable fractured zone is developed in the vertical pressure-relief and horizontal tensile zone of rock stratum above goaf, while the top interface depth is 220.92 m, and the average flushing water leakage in borehole is 0.50~0.71 L/(s•m).Meanwhile, the weak water-bearing section in the lower part of Cretaceous sandstone and sandy conglomerate confined aquifer is located in the fracture zone, while the rock strata below the depth of 200 m are in the state of water filling, and the apparent resistivity is 20~40 Ω•m. In addition, the rock strata which are above the permeable fractured zone, and below the depth of about 120 m, are in the states of vertical pressure-relief and horizontal compression, as well as bed separation development, and no water filling. Thus, the coal mining under the reservoir is safety and reliable.

Failure characteristics of floor “three-zone” along the inclined direction of coal seam

SUN Jian

2014, 31(1):  115-121. 

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To research the failure characteristic of coal seam floor with a certain dip angle, based on the theories of ground pressure, a mechanical model of workface lateral floor was established by considering the dip angle of coal seam, and the calculation formula of the maximum failure depth of workface lateral floor was deduced based on the Mohr-Coulomb yield criterion. The mining-induced failures in floor can be divided into three zones along the inclination, and the failure forms present a “spoon-shaped” state, which is larger than the width of workface. Finally, the influencing laws of dip angle on floor failure depth, failure form and the position of the maximum failure depth were simulated by FLAC3D. The results show that: 1) the plastic failure depth of floor increases with the increase of workface width, and increases first and then decreases with the increase of coal seam dip angle. It will reach the maximum failure depth at 30°, and is more likely to induce shear sliding failure; 2) the maximum plastic failure depth position of coal seam floor gradual deviates from the middle of workface and downward with the increase of dip angle of coal seam, and the wider the workface, the farther the deviation.

Impact of parameter on Knothe time function and its calculation model

HU Qing-feng, CUI Xi-min, KANG Xin-liang, LEI Bin, MA Kai-feng, LI Lei-cheng

2014, 31(1):  122-126. 

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Based on the analysis of the influence of the Knothe time function parameter, This paper puts forward that before the Knothe time function is convergent, for the same point in time, the smaller the value of becomes, the smaller the Knothe time function value becomes, and vice versa. The influence of the different parameter on the Knothe time function value is very significant, especially when t∈[0,0.2]. According to the general laws of surface subsidence and the size at which the gob reached the full extraction, a new evaluation parameter model of Knothe time function (named the probability integral calculate the parameter method) was established. By comparing the measured value and the calculated value of the model of Pingan coal mine, Fuli coal mine and Suncun coal mine, the correctness of the model is verified. By applying the model to several observational subsidence data of the strike line of the 29401 face, and comparing the measured data and predictions, the practicality and reliability of the Knothe time function parameter calculation model is established in this paper.

Rockmass structural plane digital recognition and stope stability classification based on the photographic surveying method

ZHAO Xing-dong, LIU Jie, ZHANG Hong-xun, YOU Wei, LIU Feng-tao

2014, 31(1):  127-133. 

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Stope rockmass structural plane distribution is one of the important indexes to evaluate the stability of stope and its surrounding rock mass. Therefore, in this paper, the 3-D digital measurement system (ShapeMetrix 3D) is employed to survey and collect the digital information of the parameters of rockmass structures plane that include rock mass occurrence, joint set number, joint spacing, liner density of structural plane etc of -630m stage stope at Xincheng Gold Mine. Based on the digital joint structure characteristics, the Q-system and RMR system are employed to analyze and classify the stability of stope rockmass, combining geostress measurement result and rock mechanics parameters. The stability of stopes is analyzed by using the Q-system and RMR-system. Assessments are conducted at the hanging wall, orebody and footwall of different stopes. By contrasting the assessing results of two kinds of rock mass rating system, the hanging wall and orebody have poor Q and RMR values, and the foot wall has fair conditions, which indicates the fair or poor stope stability. The stability analyzing method is very effective to assess the stope stability at Xincheng Gold Mine and it provides the reliable basic data for choosing the right stope structure parameters and roof supporting forms.

Research on the dilatancy influencing factors and dilatancy prediction in deep working face coal seam

HU Zu-xiang, XIE Guang-xiang, JIANG Fu-xing, ZHANG Li-qing, TANG Yong-zhi

2014, 31(1):  134-138. 

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This paper has conducted a comprehensive analysis on damage deformation characteristics of coal containing gas and working face coal stress environment based on coal containing gas mechanics experiment. The fuzzy comprehensive analysis method is used, and influencing factors and its significance of dilatancy is determined in the working face coal seam. Using the Binary Choice Model, dilatancy prediction discriminant model in working face is built. The results show that mining stress, compressive strength and the original rock stress are the key influence factors of coal mass dilatancy in working face. And mining stress is the main control factor in these three factors, so reducing mining stress is the most effective way to control deep coal dilatancy. A new method of dilatancy prediction is founded based on Binary Choice Model, the mining stress being the main control factor. Consequently, the purpose for effective predicting and controlling dilatancy in working face coal is achieved.

Numerical simulation of explosion-proof safety distance and propagation characteristics of gas deflagration

JIANG Bing-you, LIN Bai-quan, CHEN Jian, GUO Chang, ZHANG Peng

2014, 31(1):  139-145. 

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In this paper, an explosion roadway with the length of 100 m and cross-sectional area of 0.08 m×0.08 m was established by using AutoReaGas Software, where the methane/air mixture gas with 9.5% fuel concentration is distributed uniformly within the first 10 m of the roadway. The results show that the maximum explosion overpressure presents a changing trend of decreasing, increasing, and decreasing again in the process of gas explosion propagation, and reaches its maximum value near the location where the flame is extinguished. Both the maximum combustion rate and flame propagation speed increase firstly with the increase of propagation distance, and then begin to decrease after obtaining their corresponding maximum values. The maximum overpressure and gas velocity have reduced to zero at the distance of 35 m from the ignition source, and the maximum density also has decreased to its initial value at this distance. These trends indicate that the explosion-proof safety distance is 35 m under this condition. The maximum combustion rate and flame propagation speed have reduced to zero at the distance of 17 m, which indicates that the maximum distance of flame propagation is 17 m. The occurrence of gas backflow is related to flame propagation. The research results can provide references to optimal route determination for avoiding gas explosion disasters in underground coal mines, the emergency rescue and disaster relief after gas explosion, the explosion accident investigation, and so on.

Damage evaluation and support optimization of deep vertical shaft through the coal and rock seams disturbed by array gas-discharging holes

LI Ming-jing, RONG Chuan-xin, CHENG Hua, ZHENG Shi-hao

2014, 31(1):  146-153. 

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Aiming to ensure the security of deep vertical shaft through the coal and rock seams which are disturbed by array gas-discharging holes, the disturbing mechanism is analyzed, and a damage evaluation model is established based on the damage mechanics theory. Then, the stability of disturbance coal and rock seams, mechanical response of rock excavation and shaft lining placement are simulated by numerical method specific to a km deep vertical shaft in Haizi coal mine. Based on the analysis result, support scheme of deep vertical shaft through the coal and rock seams disturbed by array gas-discharging holes is optimized. Results show that, to evaluate the damage of coal and rock seams disturbed by array gas-discharging holes, the erosion action of water in drill hole, pressure-relief and ar- ray holes effect of coal and rock seams should be considered at the same time, as the integrating of the three effect causes a larger damage of coal and mudstone stratum than the siltstone stratum. Disturbed coal and mudstone stratum is apt to be unstable in a great range. In order to ensure the stability of surrounding rock and support, firstly, before the vertical shaft pass through the relevant strata, gas-discharging holes are used in pre-grouting to reinforce the surrounding rock; secondly, during the excavate and pouring process of shaft lining, some strengthened initial support is constructed in time, and the tensile properties of shaft lining concrete is improved; thirdly, after the shaft lining pass through the disturbed strata, the surrounding rock is reinforced by backfill grouting in time.

Controlling effect of extremely thick igneous rock on gas occurrence of underlying coal seam

WANG Wei, CHENG Yuan-ping, WANG Liang, WANG Hai-feng, LU Shou-qing, JIANG Jing-yu

2014, 31(1):  154-160. 

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To study the controlling effect of extremely thick igneous rock on gas occurrence of underlying coal seam, five coal samples had been selected in igneous rock covered areas with different thickness in No.10 Coal Seam of Haizi Coal Mine. The changes of coal firmness coefficient, initial methane diffusion velocity, methane adsorption constants, outburst risk index value, etc, as the increasing of igneous rock thickness were tested in this paper. Meanwhile, the proximate analyses, micro porous measured by carbon dioxide, scanning electron microscopy and maceral were used to study the influence of igneous rock on the coal quality and pore structure. The results show that the distribution of extremely thick igneous rock plays a control role in the coal property and gas occurrence of underlying No.10 Coal Seam. The metamorphic degree of No.10 Coal Seam has been improved under the thermal evolution and thermal metamorphic effects of igneous rock. The underlying coal seam is gradually improved from long flame coal in without igneous rock covered area to lean coal under the extremely thick igneous rock. With the thickness increase of overlying igneous rock, the micro porous of No.10 Coal Seam developes, the ability of gas adsorption and reservoir enhances, and the gas content increases. The strength of underlying No.10 Coal Seam decreases under the squeezing action of igneous rock intrusion, and soft coal layer can be easily formed in local area. Thus, the risk of coal and gas outburst increases.

Coal and gas outburst simulation experiment reacted by microseismic monitoring

LEI Wen-jie, LI Shao-quan, SHANG Peng, ZHANG Yao, XU Jiang, WANG Zhen-gang, LI Qing-song

2014, 31(1):  161-166. 

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In this paper, by using the large-scaled coal & gas outburst simulation experiment system, as well as the developed materials in cavity opening with the property of high sealing performance and powerful rheological behavior, the automatic outburst process was simulated under the comprehensive action of vetical and horizontal stresses. Meanwhile, the whole experiment processes were monitored by microseismic system with high sensitivity installed on the cavity surface. The gas pressure within the outburst assembly cavity in each stage was monitored, and the dimension and shape of the outburst cavity were outlined. The analyzed frequency ranges from 0 to 2 000 Hz. By the optimization of wavelet primary function, the maximum decomposition of wavelet packet was determined. Then, the frequency characteristics in the four stages was acquired by the decomposition and reconstitution of signals based on Wavelet Packet Transform. The results show that the signal frequencies in the inoculation stage are in the high frequency range, while the signals in the excitation stage start to broaden and the low frequency signals appear. In addition, the frequency in the outburst stage is distributed in the full-band, while the signals transmit from the low frequency band to high frequency in the residual stage. The research results can provide reference to the early-warning of outburst by microseismic monitoring.