Journal of Mining and Safety Engineering

Theory and Applicable of Yield Mining at Ending Stage of Fully-Mechanized Face in Shallow Seam at Shendong Mine Area

WANG Xiao-Zhen, JU Jin-Feng, XU Jia-Lin

2012, 29(2): 151-156.

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According to the problem of support crushing accidents at the ending stage of fully-mechanized faces in Shendong mining area，theory analysis and practice method was adapted to research the principle and application of yield mining．The results show that yield mining is a kind of skill that can avoid the influence of ground pressure at ending stage of fully-mechanized faces by stopping mining at a proper position before removing，which can change the starting location and decrease the length of continuous pressure by reducing mining velocity and create a non-pressure surroundings．While the width of interval pillars during yield mining must be determined by taking interval pillars’ stability and non-pressure at ending stage as premise．Four probable situations are put forward according to the pressure law before stopping mining and pressure behavior during stopping mining．Yield mining was successfully used at the ending stage of NO.21305 fully-mechanized face in Daliuta coal mine and NO.22303 fully-mechanized face in Bulianta coal mine which realizing a safe waking face removing．

Study of Caving and Fracturing over A Longwall Panel Beneath A Goaf Mined by Room and Pillar

YANG Zhen, TONG Bing, HUANG Cheng-Cheng

2012, 29(2): 157-161.

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In order to research the process of roof caving and fracturing over a longwall panel which is beneath a goaf mined by room and pillar method，physical analog simulation has been built up in condition of geological situation of Tangshangou coal mine.In this physical model，the subsidence velocities of roof and strata fracturing have been obtained．After the subsidence velocities have been differentiated，we got the acceleration of subsidence in such kind of geological and mining condition．The data shows that the overburden released energy with a short step periodically．By the way，the larger energy released after a several short step．During this process the strata began to fracture，and especially，the pillar collapsed quickly in a goaf mined by room and pillar method．The caving process started from pillar and roof to the surface quickly．The fracturing speed of strata is quicker than one in a virgin overburden.

Strata Movement Control due to Bulk Factor of Backfilling Body in Fully Mechanized Backfilling Mining Face

HUANG Yan-Li, ZHANG Ji-Xiong, ZHANG Qiang

2012, 29(2): 162-167.

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Fully mechanized coal mining and backfilling with solid waste，such as waste rock，fly ash，and loess，creates advantages for effective mining of coal under buildings，railroads，and water bodies．According to field geological conditions and the equal mining height concept，we analyzed the effect law of the equal mining height arose from different bulk factors of backfilling bodies．Moreover，we numerically simulated the strata movement and surface subsidence control under the condition of different bulk factors，and put forward that the allowable bulk factor of backfilling body is 15% based on allowable ground subsidence．Finally，the engineering application confirmed that the strata movement controlling is effective，and the surface buildings and facilities are not severely influenced．The research results has provided references for the effective execution of fully mechanized coal mining with solid waste backfilling．

The Study on the Deformation Process of Overlying Strata in the Deep and Thin Bedrock

JIA Ming-Kui

2012, 29(2): 168-172.

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According to the geological condition of buried deep with thin bedrock coal seam in the 11011 working face of Zhao-Gu No.1 coal mine，the paper discussed the conditions of thin bedrock water gushing and running sand coal seam by using the coal mine field investigating and statistical analysis method．After analyzing and calculating the working face roof’s structure instability mode by using the theories of ‘masonry beam’ and ‘step beam’ we have analyzed the overlying strata damage，migration evolution rule of fractures．The results show that and the height of the working face roof water fracture zones is about 48 m．Therefore，some preventive suggestions and measures have to been taken into practice when mining a coal within such a range．The measures can also guide other coal mines with similar geological condition．

Evaluation Model on the Coal Scientized Mining Coefficient by the Subjective Dynamic Weight

LI Dong-Yin, ZHOU Ying, LI Hua-Min

2012, 29(2): 173-177.

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Scientized mining is the objective requirements of human beings for coal mining，and the advanced stage for human obtaining coal resources from the nature．The scientized mining has been related to the human social and ecological environment safe and harmonious development，and also healthy and sustainable development．Based on the connotation of scientized mining，guarantee measures and objective analysis of the mining conditions，confirmed the scientific evaluation system which composed of by 5 first-class indexes，33 second-class indexes and 64 third-class indexes．By the use of method with experts-input-parameter，the standard value method，switching function method, sub-function method，qualitative value method，and other means to achieve the evaluation index of the dimensionless processing．Combined with industry characteristics，respectively，in the process of weight determination and quantification，give full play to the role of evaluation expert，and by optimizing subjective weighting of experts participation together，realizes the target weights of evaluation system in dynamic．Using scientized mining coefficient (ScMC) to quantify expression the scientized mining level of the evaluated mine．

Study on Deformation Mechanism and Stability Control of Surrounding Rock in Roadway for Deep Underground Mining of Oil Shale

ZHAO Hong-Chao, CAO Sheng-Gen, ZHANG Ke-Xue

2012, 29(2): 178-184.

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According to the situation that the typical roadway of oil shale at the middle Jurassic period in Yaojie mine field，Minhe basin，could not meet the normal need of using. In this paper，we combined with the sedimentary environment and main physical and chemical properties of oil shale，used the nonlinear strength degradation creep model of surrounding rock，numerical simulation to analysis the rule of stress and deformation speed of surrounding with time，and pointed out that the massive clay mineral in oil shale with the influence of weathering and water physical easily swells and collapses．While time effect on the strength of surrounding rock and unreasonable support parameter plays an important role in the stability of surrounding rock．Based on the previous study，the appropriated rock control technology of “high resistance and yield pattern，occlude crack，cut off the water ” has been concluded．Through the use of high pressure yielding anchor bolt with butterfly pallet，guniting and grouting，the stability of surrounding rock has been implemented．Compared with former support technology，the result showed that control technology of surrounding rock proposed effectively，reduced the deformation of surrounding rock and guaranteed the stability in the field application in the concentration transportation roadway 800-850m in deep.

Visco-Elastoplastic Analysis on the Deep Underground Roadway Surrounding Rocks Considering Softening and Swelling

SU Hai-Jian, JING Hong-Wen, ZHANG Chun-Yu

2012, 29(2): 185-190.

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With the coal mine excavated deeper gradually, strain softening, swelling fracture and rheology of the rock appear around deep and high stress underground roadways. The stress, displacement and radius of cracked region are obtained, after linear softening model is built and visco-elastoplastic mechanics analysis on the deep underground roadway surrounding rock is done. According to an example based on the research background of the mudstone roadways in the shaft station of Yuncheng coal mine in Shandong province, the failure and deformation character of rocks have been analyzed with the influence of swelling fracture and strain softening. The result shows that both swelling and softening have played an important role on the deformation of roadway and the thickness of cracked region. The deformation and failure under coupled action is more serious than the other situations, and softening action is more disadvantaged to the stability of surrounding rocks than swelling. After comparing the data from actual measurement with the theoretical value，it proves the correctness of the research.

The Study on Coordination for Avoiding Impact Using Bolt and Anchor Cable with Large Deformation

WANG Ping, JIANG Fu-Xing, WANG Cun-Wen

2012, 29(2): 191-196.

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Under the roadway support of large deformation caused by strong impact，it could be safety when bolt coordinates with anchor cable on anti-rockburst supporting. That kind of support not only relates with the safety during construction，but also influences the long-term safety of roadway support. When bolt and anchor cable union support the roadways with large deformation is used in condition of strong impact，the bolt and anchor cable will be easily destroyed．So the paper introduces the main construction and yield pressure features about the large deformation bolt（anchor cable）suited to the roadways with large deformation caused by strong impact．The coordination of anti-rockburst principle and design criteria of the research about bolt and anchor support has been analyzed at the same time．On the base of experimental research of the large deformation of bolt (anchor cable)，the experimental design method under different impact conditions have been given．Research result has certain reference value to the support design construction of the roadways with large deformation caused by strong impact．

The Surrounding Rock Deformation Rule and Control Technique of the Roadway Driven Along Goaf and Heading for Adjacent Advancing Coal Face

WANG Meng, BAI Jian-Biao, WANG Xiang-Yu

2012, 29(2): 197-202.

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The roadway driven along goaf and heading for adjacent advancing coal face was in full procedure influenced by the dynamic pressure occurred by the lateral main roof broken，turned and stabilized of the upper sectional coal face，the surrounding rock would occur large deformation and difficult to maintain．This paper researched the surrounding rock deformation rule and control technique by theoretical analysis，numerical calculation and field test. The result shows that this roadway would occur asymmetrical deformation，small coal pillar and roof deformed greatly，improve support strength of small coal pillar and roof was the key to remain the roadway stable．According to the research，the better supporting technology is shown as follows: 1）Reasonably determine the width of small coal pillar，kept roadway in stress decreasing zone；2）High strength and large elongation anchor controlled deformation of surrounding rock；3）Reinforced support of the small coal pillar and roof to improve the carrying capacity of key parts．According to the engineering application in Qipanjing Mine，the supporting technology effectively controlled the deformation of surrounding rock of roadway，and achieved good results．

Loose Regularity of Bolting and Surrounding in A Non-Soft Floor and Roof Gateway

XIN Ya-Jun, GOU Pan-Feng, YUAN Dong-Feng

2012, 29(2): 203-208.

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Analyzing the loose regularity of gateway surrounding is the base for optimum bolting．After analysis of the relationship between surrounding loose characteristics and bolting in non-soft roof and floor gateway，the paper calculates theoretically surrounding loose scope of non-soft floor and roof gateway，obtains the scheme of bolt-mesh-cable coupling supporting in non-soft roof and floor gateway，analyzes surrounding loose regularity of non-soft roof and floor gateway before and after bolting by numerical calculation，and monitors with drilling and detects with ultrasonic surrounding loose scope in test gateway．Results show that surrounding loose scope of non-soft roof and floor gateway lies in both two angles of roof and the middle of two sides．Two sides show semicircle destruction，roof saddle destruction．Surrounding loose scope reduces and surrounding stress transfers from two roof angles to deep in two floor angles along two sides after bolting．Bolt (cable) coupling supporting in roof and floor angles is favorable for stability of gateway surrounding．

Bolt-Cable and Wire-Netting Combined Support Research of Large Deformation Coal Entry with Soft Roof and Floor

QIN Guang-Peng, JIANG Jin-Quan, SUN Sen

2012, 29(2): 209-214.

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The coal entry’s roof and floor of Heigou Co．Ltd were soft strata．It was analyzed in theory and numerical simulated by Flac3D software of the surrounding rock weak structure deformation and bolting support mechanism that in order to resolve the serious deformation of the coal entry under shallow depth．The results show that the clamping action produced by bolting support result in the formation of arched support body of shallow rock which enhance the self-bearing capacity and integral stiffness．It is the floor corner bolts which play an important role in controlling the heave that induce floor peak stress area shift to the deep and reduce the stress-floor heave degree．The anchor cable supports reduce the tensile stress area and strata damage degree and increase the integrated stability of roof-floor seam．The flexible structure formed by steel belt and metal mesh prevent the damage develop to the deep．The combination of bolt and cable and wire-netting can achieve the effective support of the large deformation coal entry with soft roof and floor．

Numerical Research on Reasonable Width of Coal Pillar in the Double Gob-Side Entries

SI Xin-Yan, WANG Wen-Qing, SHAO Wen-Gang

2012, 29(2): 215-219.

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In order to maintain the stability of double gob-side entries of the 3405 fully-mechanized caving face at a coal mine，the reasonable coal pillar width of the double gob-side entries should be first determined．Based on the geological conditions，the FLAC3D was used to simulate the distribution law of stress，displacement and plastic zone in surrounding rock of the gob-side entries for coal pillar widths of 2，4，6，8，12，20 m．The results show that as the width of gob-side pillar increases the vertical convergence of the entries first decreases，then rises and last decreases again，while the horizontal convergence initially rises and then decreases；when the width of pillar between two entries increases the surrounding rock displacement of the entries decreases on the whole；the peak stress and plastic zone of coal pillars first increase and then decrease with the rise of the pillar widths．After the comprehensive analysis of the simulation results both in technology，economy and effect，we know that the 4m wide coal pillars of both along gob side and between entries are reasonable for the double gob-side entries because the coal pillars are in low stress region and more coal can be mined．According to the findings，the double gob-side entries were excavated and supported with dynamic superposition technology，which successfully solved the supporting problem of the double gob-side entries．

Study on Surrounding Rock Control for Mining Roadway of the Overlying Protected Seam in Ascending De-Stressed Mining

WANG Cheng, DU Ze-Sheng, ZHANG Nian-Chao

2012, 29(2): 220-225.

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Surrounding rock control in the overlying protected coal seam is a challenging topic of de-stressed mining of multi-seams．Based on current research on roadway control，a numerical simulation model was established to study stress field and fissure field before and after roadway excavation during underlying mining．Meantime，a physical simulation mode with the complex textured-roof and varying thickness was used to study roadway instability and collapse caused by dynamic pressure as well．The results show that when thickness of the roof is bigger than that of the bolted depth. The roadway situation is in the worst and the roof has the greatest possibility to lose its stability．Then a series of control principles have been proposed，such as strengthening roof，reinforcing both sides，strengthening the key area and strengthening bolted area．Therefore, combined supporting technique of tridimensional cable bolt beam structure based on new “three-high” bolt has been put them into practice finally，which showed that a better supporting effect was obtained．

Influence of Key Stratum on Waterproof Coal Pillar Size in Steep Seam

LI Yong-Ming, LIU Chang-You, HUANG Bing-Xiang

2012, 29(2): 226-231.

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To provide theory basis for safety mining of steep seam under water body，the UDEC2D numerical calculation is used in this paper to analyze the influence of key stratum in overburden on water flowing fracture distribution and waterproof coal pillar stability，based on the occurrence conditions of coal-rock seams and hydrogeology conditions in South No.2 District of Longhu coal mine．The results show that when there is no key stratum in overburden，the water flowing fracture in steep seam mining presents“ear style”distribution．When there exits key stratum in overburden，the water flowing fracture is mainly composed of bed separated fracture parallel to the bedding face，and will be parabolically increased in tendency with mining height．In addition，the water flowing fracture zone begins to develop upwards the key stratum and its upper strata after the first breakage of main roof．The exit of key stratum in steep seam can enlarge the falling range of waterproof pillar obviously，and the water body is more easily to enter into the goaf along the plastic failure zone of waterproof pillar．Hereby，the strip and up-dip backfilling mining method is designed，and the corresponding measures are adopted to reinforce the waterproof pillar，so as to ensure safety mining of steep coal seam under water body．

Multi-Field Coupling Mechanism of Seepage Damage for the Water Inrush Channel Formation Process of Coal Mine

LI Li-Ping, LI Shu-Cai, SHI Shao-Shuai

2012, 29(2): 232-238.

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Gradualness failure formation process of water inrush channel is the key problem for study on water inrush mechanism of mining, sustained coupling effect of seepage damage induced by double effect of groundwater and mining disturbance finally leads to the formation of rupture channel. Calculation program considering the double failure criterion of tension shear and compression shear for rock mass under the groundwater effect, in order to get the catastrophe evolution process of crack initiation, propagation, transfixion and channel formation for surrounding rock of water insulation under mining influence, coupling effect of stress and seepage damage for the catastrophe evolution process has been analyzed, and the formation trajectory of water inrush channel has been accurately located. Based on the calculation results of numerical experiment, water inrush channel finally forms due to strength decreased of rock mass induced by the sustained coupling effect of stress and seepage damage, and surrounding rock of water insulation experiences group crack initiation, propagation and transfixion, when the water inrush channel of group cracks suddenly connects to each other, rupture damage energy of rock mass increases sharply, shearing stress of rock mass near the channel suddenly drops, permeability coefficient and discharge increase sharply, precursor information of water inrush has been pregnant with the different physical field of rock mass at the channel path.

Research on the Effect of Coal Mining on the Aquifer of Quaternary Loose Soils

JIAO Yang, BAI Hai-Bo, ZHANG Bo-Yang

2012, 29(2): 239-244.

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In order to make a comprehensive analysis of coal mining on the aquifer of Quaternary loose soils，Zhangcun coal mine in Lu-an mining area has been chosen to be the research field．After theoretical analysis，numerical simulation and actual observation data contrast，we have found the rule of the water flowing when mining 6 m thickness of coal seam in condition of analyzing the mining of shallow coal to deep coal．The results show that as follows：In the region where the depth of coal seam is less than 110 m，the water flowing fracture would break the aquifer of Quaternary loose soils by breakthrough the water-resisting layer at the bottom of the Quaternary and develop to the artesian aquifer；Though the fissure water in weathered zone could reach to the coalface through the water flowing fracture which has developed to the weathered zone，and there is little impact to the aquifer of Quaternary loose soils in the area that the depth of coal seam between 110 m to 190 m；If the depth of coal seam is more than 190 m，the water flowing fracture only exist in the intact bedrock, and the sandstone fissure water over the roof could flow into the coalface．According to the analysis，the mining in Zhangcun coal mine where the depth of coal seam with 6 m height more than 190 m，there is almost no any influence to the aquifer of Quaternary loose soils．

The Distribution of Cracks and Its Mechanism of Tunnel Reinforced by Bolts Under Top Explosion

WANG Guang-Yong, REN Lian-Wei, GUO Jia-Qi

2012, 29(2): 245-249.

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Distribution of cracks and its mechanism of the tunnel reinforced by bolts were studied by numerical analysis．It is proved that numerical results are reliable by comparing the law of stress wave propagation and distribution of cracks．With stress wave propagation，cracks produced by stress waves were formed in free surface of top and tunnel，and some cracks were distributed in two sides of arch foots and between bolts．Comparing cracks of the tunnel with no support and the tunnel reinforced by bolts，the cracks of the tunnel with no support are wider and thicker than anchored tunnel．As a result, it shows that the anchored effect is very good．

Study on the Relationship Between Subsidence Coefficient and Mining Degree Under A Thick Alluvium Stratum

CHEN Jun-Jie, ZOU You-Feng, GUO Wen-Bing

2012, 29(2): 250-254.

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Mining effect plays key role to control deformation of the surface，and whether value of subsidence coefficient is precise or not can directly determinate the accuracy of the prediction results of surface movement deformation．In order to discuss the relationship between subsidence coefficient and mining range under thick alluvium，based on the observation data’s of surface movement observation stations under thick alluvium，the influence degree of thickness of alluvium to supercritical mining degree was studied，the unreasonable reason was proclaimed that tradition method estimates mining degree，then stress distribution of overlying strata and movement mechanism caused by mining were analyzed under thick alluvium．Then the estimation criterion that the bedrock and alluvium is regarded as the different composite medium was provided for mining degree，by calculated and analyzed，the critical mining width was proposed for supercritical mining，and subsidence coefficient was obtained under thick alluvium. Compared with actual measurement，subsidence coefficient was in accord with actual situation comparatively，which provided science prediction for“under railways，under water bodies and under buildings”under thick alluvium in mine-area．

Sensitivity Analysis of Influence Factors on Interlayer Separation of Complex Roof

WU De-Yi, GAO Hang, WANG Ai-Lan

2012, 29(2): 255-260.

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n order to analyze the sensitivity of influence factors on interlayer separation of complex roof，size of construction surface and interlayer separation was simulated by orthogonal experiment which had six factors with each factor having five levels that was original rock stress，rock properties of complex roof，tunnel width，rock thickness of complex roof，cohesion and internal frication angle of construction surface．The results showed that tunnel width and rock thickness of complex roof had obvious influence on interlayer separation and construction surface separation，with the increase of tunnel width and decrease of rock thickness of complex roof，the size of interlayer separation and construction surface separation linear increased．Rock properties in certain range had some influence on interlayer separation and more influence on construction surface separation．Internal frication angle and cohesion of construction surface had little influence on interlayer separation and construction surface separation．

Stope Structural Parameters of Panel Isolation Pillar Numerical Optimization

LUO Zhou-Quan, GUAN Jia-Lin, FENG Fu-Kang

2012, 29(2): 261-264.

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In order to take full advantage of the mineral resources and improve resource utilization, it is an important to be considered for a large copper mine to effectively recover temporary panel isolation pillar. Stope structure parameters of panel isolated pillar have been determined to be reasonably determined to safely and efficiently recover panel isolated pillar, at the same time stope and pillar stope’s safe and efficient have been sure in the first mining area. On the basis of comprehensively analyzing geological overview, mining pressure and mining situation of the mine, three stope structure preliminary plans were proposed by using numerical simulation method optimized stope parameters of panel isolated pillar. The stope could be in the most favorable mechanical state after obtained the structural parameters and mechanical response characteristics of the stope with the changing structural parameters. The results could provide technical support for safely and efficiently mining panel isolated pillar.

Analysis and Implementation of Surface Mine Slope Stability Based on Bishop Method

ZENG Wei-Guo, CHE Zhao-Xue, LI Xu

2012, 29(2): 265-270.

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The accuracy of the slope stability analysis in surface mine by Bishop method was improved．Based on the study of the numerical solution for circular sliding，a method of searching for the most dangerous sliding surface is given，which is analyzed and proved more reasonable in theory．And the moving trace of circle center as the length of radius progressive increases in presupposed step length is modified．At the same time the accurate variation range of radius and the distance of fissure is derived，which also shows the relationship between the slope angle and height．When the cohesion，the internal friction angle and the density of various rock layers are confirmed the influence of the layer structure is considered，which is more practical．We put forward the program implementation of calculating the stability coefficient of circular arc sliding and the finale slope angle in surface mine slope，including the situations of searching for the most dangerous sliding surface and the slope of layer structure，and the program algorithm flow is introduced．We designed the VB program of calculating the stability coefficient and the finale slope angle in surface mine slope，of which the result is acceptable，and we can check the stability coefficient in different slope angles．

Division of Spontaneous Combustion “Three-Zone” in High-Gas Goaf Based on Oxygen Concentration

SONG Wan-Xin, YANG Sheng-Qiang, XU Quan

2012, 29(2): 271-276.

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The oxygen concentration method is the most effective and most commonly used method in dividing spontaneous combustion “three zone” in low-gas goaf in engineering practice at present. But this method cannot be directly applied to high-gas goaf, because it neglects gas concentration. Based on the principle of chemical dynamics and theoretical derivation, the division standard of the spontaneous combustion “three zone” in high-gas goaf was proposed, and spontaneous combustion “three zone” in actual high-gas goaf was divided by this standard. The result was tested and verified by measuring and analyzing the temperature of residual coal in goaf. The study provides guidance for prediction and prevention of spontaneous combustion in high-gas goaf.

Study on the Initial Released Gas Expansion Energy Property of Imitation Tectonic Coal

WANG Hao, JIANG Cheng-Lin, YANG Fei-Long

2012, 29(2): 277-282.

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Through theoretical analysis and the trial of imitation tectonic coal which is made of certain fragmentation degrees of non-tectonic coal, the thesis studies on the Initial Released Gas Expansion Energy Property of Imitation Tectonic Coal and discusses the possibility of taking the place of tectonic coal with imitation tectonic coal. The result of lab test proves that gas pressure, gas released volume and expansion energy of initial released gas of both tectonic coal and imitation tectonic coal all keep consistent with negative exponent curve. They stand still 1 000 ms later while cumulative volume of released gas is increasing continuously, and decay rate of expansion energy in the super critical state is smaller than that in the subcritical state. At the same time there is an inflection point at critical pressure. Expansion energy of initial released gas of imitation tectonic coal which has the same fragmentation degree as tectonic coal is equal to that of tectonic coal approximately. It is very significant to solve the problem of making wrong determination using non-tectonic coal instead of tectonic coal in coal and gas outburst identification, which caused by the difficulty of collecting tectonic coal.

Method and Experimental Study on Draining Water and Cinder by Jet in Gas Drainage Hole

LI Dong, LU Yi-Yu, WANG Jie

2012, 29(2): 283-288.

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Water and coal cinder in the downward drainage holes influence the effect of gas drainage. A new method is proposed to drain water and coal cinder by jets. A set of device for drain water and cinder by jets is designed. The feasibility of this method is verified by using orthogonal test and the influences of working parameters on the device performance are also researched. The results show that the device performance is most affected by compressed air pressure p. The amount of water and coal cinder increase at first and then reduce as p increases indicates that there exists an optimal air pressure p* making the device performances the best. There is a critical depth Hnp of drainage holes. When the depth of hole is less than Hnp, the amount of water and coal cinder keep invariant. However, the amount decreases gradually when the depth of hole is more than Hnp. If all other conditions do not change, the amount of water and coal cinder increase gradually as the water depth in the holes increase. The p* of the device for water and coal cinder drainage is 0.55 MPa obtained by experiments. The method of draining water and coal cinder by jets is feasible and simple to operate and available to drain water and coal cinder effectively in the drainage holes of coal mine.

Study on New Drilling Technology in Soft and Outburst Seam

WANG Yong-Long, SUN Yu-Ning, DI Xin-Xian

2012, 29(2): 289-294.

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Low spiral drill rod is a new type of drill rod，which invented to solve the drilling problems of soft and outburst seam. In order to fully play the advantage when low spiral rod applied to soft coal seam drilling，the paper analysis effect on the slag removal conditions due to low spiral rod in different spiral convex edges width and pitch change according to the practical applications and establish corresponding numerical model of the slag removal. According to the dynamic parameters of the matching drilling rig in engineering application，the strength of low spiral rod has been analyzed. The result of study shows that it is optimum to slag removal result，and the minimum safety factor of drill rod strength for 1.87 with the convex edges width l=14 mm，pitch s=80 mm. It is reasonable to optimization parameter design of machining low spiral drill rod. Depth and efficiency increase significantly showing when drilling industrial experiment carried out.

Lean Methane-Air Premixed-Gas Heating Process Research

XIAO Qi, DENG Hao-Xin, lv Yuan

2012, 29(2): 295-300.

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The methane oxidation and heat release phenomenon had been found in low concentration methane/air premixed gas (methane concentration is lower than 25% low explosive lever) preheating process in coal mine ventilation air methane regenerative oxidizer. How different concentrations of methane oxidation and heat release effect on premixed gas preheating process were investigated in this paper. The FLUENT software was used for numerical simulation of premixed gas preheating process with unsteady flow field and chemical reaction. The results show that premixed gas preheating temperature is obviously higher than air preheating temperature and surface temperature of regenerative ceramic because of methane oxidation and heat release when methane concentration is higher than 0.2% and preheating temperature is higher than 900℃. When methane concentration of premixed gas increases, the preheating length of premixed gas and quantity of regenerative ceramic decrease at the same time. The numerical simulation results and the experimental results agree well with each other.

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