Table of Content

15 September 2013, Volume 30 Issue 5

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Feasibility of application of TBM in construction of deep coal mine and its key scientific problems

LIU Quan-sheng, SHI Kai, HUANG Xing

2013, 30(5):  633-641. 

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The article analyzed the present situation of reserves of coal resources and exploitation, and presented that the coal mine in China had come into the time of deep exploitation and would soon come into 1000-meter-below exploitation time, when the construction of deep coal mine would have the tendency of upsizing, intensification and modernization. The status quo and difficulty of excavation in deep roadway showed that the traditional drilling and blasting method or road header can’t meet the requirements of safety and fast-speed in construction of large-scale deep coal mine below 1000 meters under complicated conditions, such as high in-situ stress, high geothermal energy, and so on. Based on the real situation of the deep roadway and various advantages of TBM in other forms of underground engineering, application of TBM in deep coal mine construction is put forward, and construction cases of TBM in coal mine are summarized. Finally, a series of key problems are presented based on the complexities of geological environments and mechanical behavior of deep rock mass.

Advancing solid backfill mining on condition of two entries pre-excavation

ZHOU Nan, ZHANG Ji-xiong, MIAO Xie-xing, ZHANG Qiang

2013, 30(5):  642-647. 

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Restricted by geological conditions and existing roadways layout of some mining area under buildings, railways, and water bodies, to guarantee the controlling effect of solid backfill mining to strata movement and ground deformation, the article proposed solid backfill mining technology on condition of two entries pre-excavation, analyzed its principle and the technical difficulties, established advancing solid backfill mining system on condition of two entries pre-excavation, optimized key equipment structure for backfill mining and corresponding layout, and designed an integrated technique and a comprehensive system based on the technical features of both solid backfill mining and gob-side entry. On-site practice shows that the filling ratio of 90.6% is achieved, the cross section of the retained entries account for more than 90% of the original one, and the maximal sinking value of the ground is 125 mm, which prove this technology can effectively control the strata movement and ground deformation. This integrated technology shows a great potential for excavating the coal resource under similar conditions.

Research on expert system of roadway supporting schemes for coal mine and its application

YANG Ren-shu, MA Xin-min, LI Qing, ZHANG Jun, BAI Xiao-sheng, WANG Mao-yuan

2013, 30(5):  648-652. 

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Concerned with geology condition，production conditions，mining conditions and rock mechanics, supporting schemes of mine tunnel is an involved problem of theory and technology. Aiming at the above-mentioned problem, the expert system of roadway supporting schemes for coal mine combines expert experience, typical engineering cases and theoretical achievements with artificial intelligence technology; establishes content-rich knowledge base of expert experience, typical engineering cases and theoretical research achievements; adopts initial program for roadway support inferred from two methods of rules and typical cases; builds the program for the roadway support model and compiles into dynamic-link library files loaded and invoked based on the secondary development technology of FLAC3D; realizes optimization of the roadway support on the basis of the initial program and generates sectional chart of roadway support automatically. An application example is presented in coal mine in Shanxi province; the results prove that the system optimization scheme is reasonable and feasible.

Study on failure evolution laws and control technology of roadway surrounding rock under mining circumstances

ZHANG Hua-lei, WANG Lian-guo, TU Min, ZHANG Ying-gui

2013, 30(5):  653-658. 

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Aiming at the situation that the surrounding-rock of the tunnel cannot meet the requirements for normal production after being repaired for several times, with No.86 return airway of Haizi colliery affected by mining as the background, the mechanical model of a special point in the floor mining- affected zone was established. It is concluded that the tunnel was in the asymmetric pressure force state, thus elastic-plastic model of the tunnel stress was established in the asymmetric pressure force state, the plastic zone width calculation formula of the tunnel surrounding rock was deduced and reinforcement schemes taking thread steel grouting bolt as the core were made. The results showed that after the floor tunnel was reinforced with supporting system taking the grouting blot as the core, the deformation of surrounding rock, caused by mining in the overlying working face, could be effectively controlled and the plastic zone width calculation of the tunnel surrounding rock was rational.

Relationship between ground stress distribution and roadway stability in deep tectonic region

XIAO Tong-qiang, ZHI Guang-hui, ZHANG Zhi-gao

2013, 30(5):  659-664. 

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In this paper, aimed at controlling the stability of roadway surrounding rock in deep tectonic stress field, relationship between ground stress distribution and roadway stability was studied. Through ground stress measurement and inversion, the deep ground stress field in Juye Mining Area belongs to tectonic stress field. Meanwhile, based on the ground stress distribution characteristics, by using similar simulation, numerical simulation and field test, the effects of buried depth, tectonic stress, roadway layout, fault, etc, on roadway stability were systematically studied. The results show that when buried depth is over 800 m, and lateral pressure coefficient is over 2.5, roadway deformation increases rapidly, plenty of shoulder bolts are broken, the shear failures in roof and floor are serious, and the thick top coal appears "fastigium" shape collapse. Meanwhile, ground stress is higher near fault structures, and the larger the angle between roadway and the maximum horizontal stress is, the larger roadway deformation is, and the more serious the damage of support structure is. Thus, the surrounding rock control in roadway roof and shoulder needs strengthening in deep tectonic regions.

Analysis on secondary support parameter of deep high-stress & broken-expand surrounding rock

HUANG Wen-zhong, WANG Wei-jun, YU Wei-jian

2013, 30(5):  665-672. 

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According to deformation features and supporting problem of deep high-stress & broken- expand surrounding rock, with Qujiang Coal Mine as an example, optimization of secondary support parameter was studied. Concrete support projects were put forward based on deformation features of deep roadway and original supporting project, these projects include the first support parameters, the secondary support parameters and the secondary support opportunity. The piecewise linear strain-softening model was used to obtain post-peak soften strength parameters of surrounding rock. Strength effect of anchorage body was considered, the concept and the calculation formula of anchor supporting strength index (ID) was put forward, and modified calculation parameters of rock mass were given. Numerical calculation was done for these sixteen secondary support projects, and comprehensive scores index (ES) of roadway stability proposed was used to optimize projects. The results showed that the eleventh project (the anchor length (la) is 8 000 mm, the low and row distance (ea×ia) is 1000 mm ×1000 mm, the displacement value of secondary support opportunity (da) is 60 mm) can not only ensure stability of roadway, but also save cost, so it is optimum scheme. Therefore, influence relation of different anchoring effects and different displacement values of secondary support opportunity action on roadway stability were respectively analyzed, and overall evaluation and designing principles of support parameters were put forward.

Bearing behavior of block wall structure in gob-side entry retaining and its application

HAN Chang-liang, ZHANG Nong, WANG Xiao-qing, LI Bao-yu, LI Zhi-bing

2013, 30(5):  673-678. 

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To investigate the adaptability of block wall in gob-side entry retaining, block wall structure form, failure process, constitutive relation and bearing capacity were studied, revealing the failure mechanism and bearing behavior of block wall structure. The results show that failure of block wall in gob-side entry retaining usually occurs in III stage, and retained entry is easily maintained in I, II stages. Axial bearing capacity of block wall should match its support resistance, and the strength of wall, roof and floor should be matched. Based on the two matching principles, a whole design process of block wall structure in gob-side entry retaining was proposed, and has been applied in Shaqu Coal Mine. The blocks with the size of 0.80 m×0.18 m×0.12 m, strength over 10 MPa and the mortar with the strength over 2.5 MPa, were designed to lay block wall with width of 1.6 m and strength between 4.3~9.3 MPa by using special masonry form, which has achieved favorable effects in gob-side entry retaining.

Elastic-plastic damage analysis for weakly consolidated surrounding rock regarding stiffness and strength cracking

WANG Wei-ming, ZHAO Zeng-hui, WANG Lei

2013, 30(5):  679-685. 

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The cracking of stiffness and strength, due to existing and development of micro cracks in elastic region, causes the loosening scope of roadway surrounding rock expanded. By defining stiffness cracking coefficient and strength cracking factor, considering characteristics of strain softening and plastic dilatancy after post-peak, the article established an elastic-plastic flow damage model for weakly consolidated soft rock under non-uniform initial stress field on the basis of damage theory and strain softening model with three linear steps; inferred analytical solutions of stresses, displacements when surrounding rock generate three different failure areas: elastic zone, elastic and plastic softening zone, and plastic flow zone; and discussed the rule on the influence of original rock stress, strength cracking, dilatancy gradient of soft surrounding rock in Luxin coal mine on damage evolution, displacement and plastic circle of surrounding rock. Results show that dilatancy gradient has great effect on damage speed and displacements in plastic zone while it has little effect on the size of plastic circle and stress responses; that original rock stress level has remarkable influence on the distribution of plastic circle of the roadway; and that the rising of stiffness and strengthen cracking coefficient will accelerate the cracking speed of surrounding rock, which should be paid enough attention in analyzing the stability of the surrounding rock and designing weakly consolidated soft rock tunnel.

Reinforcement mechanism and experimental study on continuous double shell of deep roadway

SUN Li-hui, YANG Ben-sheng, YANG Wan-bin, SUN Chun-dong

2013, 30(5):  686-691. 

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Aiming at the problem that the deep roadway was deformed seriously, and the traditional support could not guarantee stability of roadway, this paper proposed idea of reinforcement continuous double-shell of the deep roadway based on analyzing deeply the deformation characteristics of deep surrounding rock and analyzed its reinforcement mechanism. The nude roadway, anchor support, deformation of surrounding rock in continuous double-shell support roadway and stress distribution rule of roadway under different deep mining conditions were studied through imitation test with similar materials. The results showed that with the mining depth increasing, the self-stability of the surrounding rock in nude roadway couldn’t be maintained for it was damaged largely; that there was potential failure risk for the bolt support roadway because its deep surrounding in inlet anchorage zone was destroyed in abscission layer; and that the local shear failure for continuous double-shell support roadway occurred in the shallow part wall of roadway and the stability of surrounding rock was good. The example of the new-southern roadway support of Tao-er coal mine proved the reasonability of continuous double- shell’s support.

Support technology and controlling principle of surrounding rocks of coal rise entry in Wuyang mine

YUAN Yong, WANG Ji-lin, LI Qing-feng

2013, 30(5):  692-698. 

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Based on engineering practice in Wuyang coal mine, the mechanical properties of roof rock has been obtained by the triaxial compression experiment of confining pressures step longtime loading, and the surrounding rock visco-elasticity property of supporting roadway has been analyzed, and controlling principle of surrounding rock has been proposed for controlling deformation of coal rise entry in supporting practice. Four conclusions were drawn: 1) the surrounding rock deformation of roadway is a time course, the deformation tends to be stable after any load being loaded for a certain period of time, and the time span taken by reaching steady increases exponentially with increasing normal loading; 2) the rate of axial strain can be effectively decreased by raising the confining pressure when the axial strain does not tend to be stable; namely, the stability of surrounding rock deformation can be accelerated by raising the confining pressure when roadway displacement does not tend to be stable to avoid the instability of surrounding rocks; 3) roof deformation and the evolution of the plastic zones can be effectively controlled with prestressed anchor cable, but the deformation of coal side and coal seam floor can be aggravated; namely, the stability of slope of roadway sides and floor must be strengthened when the roof is supported with bolting and rope; 4) the appropriate stress transfer can be beneficial to the ultimate stability of surrounding rock, and controlling principles of step loading of one support is highly effective for controlling surrounding rock deformation of the thick coal seam rise entry.

Study on support design and parameter optimization of truss and anchor rope in the large mining height open-off cut

HAN Lei, MENG Xiang-rui, CAO Huai-jian

2013, 30(5):  699-705. 

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In order to study the truss-cable combination support mechanism in the large mining height and complex roof open-off cut, adopting theoretical analysis, field measurement, numerical simulation test method, the truss-cable support parameters in the open-off cut of large mining height 2-1101 working face were optimized. The results show that if the inclination of anchor cable is too large or too small, these are not conducive to control the deformation and plastic zone of the surrounding rock. The anchor cable inclination angle of 65°~75° is the best for truss-cable support; anchor points in the truss system must be anchored into a stable rock pressured to ensure that the truss system has a stable anchoring basis point. Truss-cable drilling depth is chosen as 9 m to enhance the stability of the roadway. The reasonable distance value of the cable drilling to roadway side is 1.5 m. It is better to control the development of the surrounding rock plastic zone when the roof bolt density is 10 in each row. The results of field measurement show that the convergence rate of roadway section is very small. The largest value of the open-off cut two sides moving closer is 145 mm. The roof subsidence maximum is 166 mm; trussanchor- combined support has a good effect on the controlling of surrounding rock in the open-off cut.

Study on migration mechanism of slipping floor heave rock mass in deep roadway and its control countermeasure

LIU Shao-wei, ZHANG Wei-guang, FENG You-liang

2013, 30(5):  706-711. 

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Along with the depletion of superficial coal in China, the mining depth is increasing, and the problem of floor heave gets more and more serious. Probing into the problem of slipping floor heave, with the plastic mechanics theory, slipping floor mass is divided into several areas and the calculation formulas of floor breaking depth and critical load is obtained. The stressed characteristic of unit body in the slipping area is analyzed according to the mechanism of bolt action, and the control measure of slipping floor heave is proposed. When applied to practice, the research results can have reference value to field production.

Research of stress distribution evolution law and influencing factors

YIN Yan-chun, ZHAO Tong-bin, TAN Yun-liang, ZHANG Ze

2013, 30(5):  712-716. 

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With laboratory tests and particle flow simulation, stress distribution evolution law and influencing factors along anchorage segment are studied. The failure process of anchor system can be divided into three stages: viscoelastic stage, de-viscosity stage and failure stage. In the viscoelastic stage, the shear stress first increases and then decreases along the anchorage segment, and the peak point is close to the pull end. In the de-viscosity stage, the bond at the pull end first fails, and then expands to the internal layer. The shear stress peak point also moves inward. Elastic modulus of anchor and anchor agent influences the stress distribution. With the increase of anchor’s modulus and decrease of anchor agent’s modulus, the intensity of stress at pull end weakens.

Strength deterioration and acoustic emission characteristics of water-bearing sandstone in uniaxial compressive experiment

YAO Qiang-ling, LI Xue-hua, HE Li-hui, ZHOU Jian

2013, 30(5):  717-722. 

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Water-bearing sandstone is widely distributed in the roof of primary mining coal seam of Ningdong coal field, which is prone to deformation and instability. In this experiment component of water-bearing sandstone is quantitatively analyzed, and time relationship between drying and water suction of sandstone is also studied. Research shows that this kind of sandstone is rich in clay minerals, and the variation of moisture content tends to keep stable six hours after being dried and soaked respectively; moreover, uniaxial compressive strength and elastic modulus of the sandstone decrease on the scale of exponential function with the increase of moisture content. The results of acoustic emission characteristics experiment show that count peak of acoustic emission of sandstone samples corresponds to the peak stress under the condition of being dried and lags behind with the increase of moisture content which shows “delaying” characteristics; in the mean time, pulse count decreases significantly with the peak of energy. According to these, technical thoughts are put forward to predict and forecast the stability of such kind of sandstone roof.

The in-situ stress measurement and practice of repeatedly stress relief on the original borehole

ZHENG Xi-gui, HUA Jin-bo, ZHANG Nong, ZHANG Lei, CAO Xu

2013, 30(5):  723-727. 

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With the stress-factors affecting the stability of tunnel-surrounding rock, based on the stress distribution of deep tunnel-surrounding rock and the principle of stress relief method, the in-situ stress measurement of repeatedly stress relief on the original boreholes was approached, and the scientific basis of discriminating the original boreholes was established. According to the measurement of basic borehole and checking borehole, the relations between the original rock stress in other measuring area and radius of the tunnel could be deduced. The project practice showed that, in Kongzhuang colliery, Datun coal mining area with buried depth more than 1 000 m, the basic borehole enter the original rock stress area at the distance about 3.7R, the original vertical stress result is 23.3 MPa，which was proved in the checking borehole and extension borehole.

Deformation law and safety degree of surrounding rock in roadway intersection

CAO Ri-hong, CAO Ping, LIN Hang, ZHANG Ke

2013, 30(5):  728-734. 

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In this paper, taking one mine as the engineering background, different numerical models of roadway intersection were established, and the deformation laws of surrounding rock in different roadway intersections were analyzed. Meanwhile, the security analysis method which both considering shear and tensile damages was used to analyze the security situation of surrounding rocks in roadway intersection. The results show that the surrounding rock deformation of roadway intersection shows different offset degrees to the acute angle side, and the smaller the intersection angle is, the more obvious the offset phenomenon is. Thus, the smaller the intersection angle is, the larger the scope needed to strengthen support in the acute angle side of roadway intersection. Meanwhile, due to the enlargement of disturbance to surrounding rock in roadway intersection, the roof and floor safety coefficient are relatively low in roadway intersection, and the regions where the safety coefficients is less than 1 are greater than other parts of roadway. Moreover, the safety coefficient of corner rock pillar from exterior to interior shows gradient changes, and the safety coefficient of rock mass outside the corner rock pillar is the smallest, which will be damaged first, and then develops gradually to the internal. When the intersection angle is too small, the percentage of damage area of corner rock pillar in the acute angle side is relatively larger, which is not beneficial to the stability of roadway. The results can provide reasonable references to roadway support in similar engineering conditions.

Research on reasonable size of waterproof pillar in mining inclined coal seam

WANG Zhi-qiang, CHEN Chao-fan, WANG Lei, LI Peng-fei, GUO Xiao-fei, GAO Yun

2013, 30(5):  735-738. 

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In the study, we calculated the pillar size of 4# coal seam with the traditional method, the analysis result showed that repeated calculation was existed in calculation of the central elastic area of the waterproof pillar in inclined seam, which results in oversized waterproof pillar left. In order to improve the disadvantages of traditional methods, in the premise of ensuring safety, we calculated the yield zone size of 4# seam, considered the impact of the overburden rock moving angle and we obtained the reasonable waterproof pillar size after the design method had been optimized. In order to further improve the recovery rate in the mining area, we comprehensively analyzed the common problems of coal pillar design and proposed optimization. Findings showed that the size of waterproof coal pillars after the design was optimized is only 42.42% of the size calculated in traditional method. Integrated the triangle coal loss of the slope segment and combined with a waterproof coal pillar size, coal loss after optimization is only 45.42% of the one in traditional method. It is calculated according to the push length of the mining area designed that nearly more than 1.58 Mt of coal can be mined between the adjacent faces. In addition, the recovery technology from the slope sections can improve the stability of equipments, which caused by the large inclination in working face.

Crack propagation induced by hydraulic fracturing in low permeability rocks using CT technology

YANG Yong, YANG Yong-ming, MA Shou, JU Yang, GUO Ying-chun, YU Yong

2013, 30(5):  739-743. 

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In order to expose the cracks propagation law induced by hydraulic fracturing in deep low-permeability reservoir stratum, a series of hydraulic fracturing physical tests of low-permeability core samples collected in situ are carried out. Using CT scanning technology and self-developed three-dimensional reconstruction algorithm, the cracks propagation and special distribution laws are featured in low-permeability rock subjected to triaxial stress and hydraulic pressure. The effects of lithology and crustal stress on cracks growth distribution features are exposed. The results show that the lithology of rock and ratios of horizontal crustal stress have great influences on initiation stress and geometric distribution features of cracks growth. The initiation pressure is always greater than the confining pressure. When the minimum horizontal crustal stress is similar, the bigger ratio of horizontal crustal stress induces more fractured cracks and small initiation stress. The direction of failure main cracks is consistent with the direction of maximum horizontal crustal stress. The main cracks appear in the middle of samples accompanied by noticeable interruption, distortion and bifurcation.

Uniaxial compressive creep test of red sandstone and its constitutive model

ZHAO Bao-yun, LIU Dong-yan, ZHENG Ying-ren, LIU Hong

2013, 30(5):  744-747. 

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In this paper, to study the creep properties of red sandstone, the uniaxial compressive creep test was carried out. Based on the test results, a non-linear visco-elastic-plastic creep model was established, and the parameters of the model were identified by using the nonlinear optimization algorithm of BFGS. The results show that red sandstone has obvious creep characteristics, and the model can better reflect the creep behaviors of instantaneous loading strain, decay creep, steady creep and accelerating creep, etc. Finally, the non-linear visco-elastic-plastic creep model was fruther developed by using FLAC3D simulation software, and the uniaxial creep numerical simulation of red sandstone was carried out. The creep curves of numerical simulation and experimental results were comparative analyzed, and the practicability of non-linear visco-elastic-plastic creep model was verified.

Response of primary electric voltage to groundwater seepage during mining operation

LIU Jing, LIU Sheng-dong, CAO Yu, WANG Bo

2013, 30(5):  748-755. 

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In view of the mine water inrush warning requirements, based on three kinds of laboratory experiments and one field test in coal mine, the dynamic response characteristics of primary voltage U to groundwater seepage was studied. During the field test, the primary voltage U and the water yield Qo in water inrush process were detected. Physical simulation experiments of steady seepage in both homogeneous and heterogeneous media have indicated that before water-saturated of solid /water two-phase medium, the variation of primary voltage U contains two stages: there exists a second-order relations between the variables of U and Qi in the first stage, while U tends to be stable, and is no longer varying with the increase of Qi in the second one. Additionally, seepage experiments under mining conditions have indicated that the seepage evolution affected by mining can be regarded as the continuation of many small steady seepage processes, and the relation between U and Qi accords with steady seepage characteristics in each small steady seepage process. Moreover, field test shows that there exits a negative correlation between U and Qo in the detection area during roof water inrush process.

Steep mining method in slippery area of end-slope under slope timeliness

HAN Liu, ZHOU Wei, SHU Ji-sen, PENG Hong-ge, LIU Lei

2013, 30(5):  756-760. 

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In order to solve the problem that a lot of coal is covered in slippery area of end-slope for steep mining is difficult to be implemented, based on the theory of slope timeliness and the steep mining technology, two strip steep mining methods as vertical and parallel propelling were proposed and the analysis system for confirming the best cut width was established. According to the systematical sequence, numerical simulation was conducted with strip steep mining method in slippery area of end-slope in Sandaoling open coal mine, which drew a conclusion that the best cut width of the slope is 60 meters, and the scheme of advancing vertical end-slope trend is recommended in the paper. The results reveal that the angle of eastern end-slope can be increased from 34° to 41 °, which will recover 193,100 tons of coal residues in end-slope. It could ensure slope stability, recycle residual coal and reduce the stripping ratio by applying strip steep mining method in slippery slope.

Study on application scope of stripping semi-continuous system in internal dumping open pit mine

WANG Hai-jun, LI Ke-min, CHEN Shu-zhao

2013, 30(5):  761-765. 

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Based on the analysis of overburden internal dumping distance in the open pit mine, this article establishes the optimization model of mining system, and provides support for the research on application scope optimization of stripping semi-continuous system. According to the characteristics of flat dipping open-pit mining, this article gives the calculation methods of overburden internal dumping distance in the shovel-truck discontinuous system and semi-continuous system. Based on comprehensive consideration of investment and operation cost effect, open pit mining system optimization model is established with the objective of minimum total cost in calculation period, and gives the calculation method of investment, stripping system operation cost and the additional costs, and the boundary conditions of semi-continuous application. The case study shows that with the increasing of mining depth and pit size, the application of semi-continuous system in upper stripping bench is reasonable, and the service range of the stripping semi-continuous system in H Mine is more than +140m level. Sensitivity analysis of fuel costs shows that the rapid rise of diesel prices in China will popularize the application of stripping semi-continuous system in large open pit coal mine.

Surface well drilling extracting gas technology in low permeability coal seams depressurized mining

TU Min

2013, 30(5):  766-772. 

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Based on depositing conditions of high gas and low permeability of coal seam group in Huainan mining area, this article analyzes the movement and failure characteristics of overlying strata, the movement and deformation characteristics of relief seam, the vertical zoning characteristics of mining fractures and stress zoning characteristics of relief seam through the analogue test. Conclusion is drawn that there are annular fracture area, vertical fracture area, and the remote relief seam fracture area from the roof of goaf in the first mining layer. According to the developing characteristics of the mining fracture areas, this article puts forward the deployment method of surface drilling in the drainage of pressure relief gas. The “ ”-type , “│”-type and “L”-type ground drilling are respectively put outside the starting cutting hole 1117(1) work face, inside the wind tunnel, and in front of the work face in Guqiao Coalmine. The relationship among the ground drilling locations, drilling type, drilling stability and relief gas drainage effect is probed into and found.

Research on dilatation energy of released gas from coal seam

YU Bao-hai, WANG De-ming

2013, 30(5):  773-777. 

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Aiming at the problems about prediction techniques for coal and gas outburst hazard, an in-depth study on dilatation energy of released gas from coal seam is conducted. Following the basic calculation methods of dilatation energy, based on the distribution rules of gas released from coal seam, the theoretical equations of dilatation energy of released gas from coal ribs and drilling boreholes have been derived respectively. In addition, by using the numerical simulation software of MATLAB, dilatation energy released from the drilling boreholes was further analyzed and calculated. The results show that there is a sharp decrease for the value of dilatation energy of released gas within the first 3 seconds in releasing time. The biggest factor affecting the energy is coal in-seam gas pressure; the second biggest factor is permeability coefficient; while the least one is the coefficient of gas content. Therefore, the dilatation energy of released gas from drilling boreholes can really reflect the instantaneous gas release ability of a coal seam. The measurement result of dilatation energy can be used as a predictor for the risk of coal outburst hazard when the coal in-seam gas pressure is determined in a field test.

Change regulation of coal seam permeability around hydraulic flushing borehole

WANG Kai, LI Bo, WEI Jian-ping, LI Peng

2013, 30(5):  778-784. 

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To research the change and distribution rules of coal seam permeability around hydraulic flushing boreholes, based on the actual occurrence conditions of coal seam, the pressure relief range of hydraulic flushing was investigated by using gas pressure and gas content methods in this paper. Additionally, the stress and permeability changes of coal mass around hydraulic flushing boreholes were simulated by RFPA2D-Flow Software. The results show that under the influence of hydraulic flushing, the pressure relief range with the radius of 5.0~6.0 m are formed around the borehole, and the stress within this area changes from 0.038 MPa to 6.545 MPa. Meanwhile, in the place about 6.8 m away from the reviewed borehole, stress concentration phenomenon is observed. The maximum principal stress is 15.85 MPa, which is basically consistent with the field investigation results. Furthermore, the distribution regulation of coal seam permeability around borehole is similar to the change trend of principal stress. While the distance away from the pressure relief range is different, the principal stress of coal mass is also various. The nearer to the borehole, the larger the decrease amplitudes of stress and gas pressure, and the larger the permeability coefficient of coal seam.

Parameters of high-pressure water jet punching technology in outburst prevention

ZHANG Jia-yong, GUO Li-wen, LUO Xin-rong

2013, 30(5):  785-790. 

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In this paper, by using ANSYS software, the stress of surrounding rock and displacement of coal mass in different roadway models after punching were analyzed comprehensively. Additionally, it was determined that the high-pressure water jet punching position should be 2/7 or so from the roadway floor, and the aperture size should be 4/15 or so of the roadway floor length. Thus, the fissures in roadway surrounding rock may develop fully, and the rock integrity can be maintained, which is beneficial to speed up the face driving. Field test has verified that renmant gas qunatity in coal seam after high-pressure water jet punching has reduced significantly, the fluctuation of electromagnetic radiation intensity in surronding rock is large, and the hole wall is deformed after punching. This shows that the fissure development in coal mass after punching, expands the gas release range around slots, reduces the gas pressure gradient of outburst coal seam, and eliminates the outburst risk.