Journal of Mining and Safety Engineering

Overlying strata movement property of fully mechanized caving angle-varied workface in steep dipping seam

GAO Xicai，WU Yongping，CAO Peipei，WANG Hongwei，YIN Jianhui

2016, 33(3): 381-386.

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Affected by variable angel, deformation, damage and movement of overlying strata in fully mechanized caving working face are more complicated than that in steeply dipping seam, which is exemplified by working face 120210 in Zaoquan coal mine. Based on its mining condition, a comparative study on movement of overlying strata respectively in steeply dipping working-face with variable angel and that with single angle is conducted through both similar simulation and field monitoring methods. The research has shown that 1) The movement law of overlying strata under different inclination angle in working face 120210 is crucially different from working face with single angle; 2) The overlying strata in the upper region with 26° angle has similar migration characteristics with inclined coal seam, the main roof in which region breaks and moves by cantilever beam structure with uniformly distributed roof pressure that values 23.7 MPa on average; 3) With an angle of 44°, the overlying strata in the lower region has similar migration characteristics with steeply dipping coal seam, and the caved rock slipped along dip direction and filled the gob; 4) The average roof pressure is 29.5 MPa, but it distributes non-evenly and varies in a large scope; and 5) As a critical transition section between the upper region and the lower region, the middle region posses overlying strata movement law of both inclined seam and steeply dipping seam. The average roof pressure in this region is 27.15 MPa and distributes evenly. The surrounding rock control principle is put forward according to the overlying strata movement property and ground pressure apparent feature in different regions. And a sub-regional method is proposed to control top-coal caving quantity according to this principle.

Similar material simulation test of steep-inclined extra-thick coal seam

CHENG Weimin，SUN Lulu，WANG Gang，HUANG Xuchao，HUANG Qiming

2016, 33(3): 387-392.

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Similar material simulation test has been applied to research the motion of overlying strata and the characteristics of fracture development of steep-inclined extra-thick coal seam mining by horizontal section top coal caving. The proportion of coal seam has been chosen as cement∶sand∶water∶ activated carbon∶coal=6∶6∶7∶1.1∶79.9 by low strength mechanical test and orthogonal test with the density of 0.913 g/cm 3 and uniaxial compressive strength of 0.076 MPa. The result of similar material simulation test has shown that 1) The overlying strata caving occurs as an integrity only after two or three mining levels have been mined; 2) The overlying strata of shallow mining levels move coordinately before caving; 3) In the deep mining level, hinge structure is formed between adjacent mining levels; 4) When the mining activity goes deeper, roof gets completely destroyed and caved after each mining level is mined; 5) The characteristics of abscission layer and fracture development are consistent with the motion of overlying strata; the depth of pressure relief is about 15 m.

Division of “four zones” in mining strata and surface movement

HUANG Qingxiang，XIA Xiaogang

2016, 33(3): 393-397.

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Based on the integration process of strata “collapse - breaking - bending - subsidence”, the strata failure and movement were analyzed. Considering the difference of the fracture development and the strata movement, the fracture zone is divided into quasi-continuous zone and block articulated zone. Thus, the four zone division of “caved zone, block articulated zone, quasi-continuous zone and continu- ous deformation zone” is set up, and the division criterion of the four zones is put forward by using hinge condition of strata structure, coefficient of rock mass stability and fractal dimension of strata fracture.

Pressure-relief mechanism of lower seam extraction after upper seam extraction

WANG Feng，XU Jialin，XIE Jianlin，GUO Jiekai

2016, 33(3): 398-402.

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With the extraction influence coal seam 5 # on longwall panel Y485 in Kailuan Tangshan coal mine as research background and based on the key strata theory, the pressure-relief mechanism of lower seam extraction after the upper seam extraction has been studied through numerical model and field ob- servation．The results have shown that during mining, the distribution of abutment stress is influenced by the key strata in the overlying strata．The key strata were fractured due to pressure-relief mining, and the abutment stress was only influenced by the key strata between the two seams．Therefore, the influ- ence distance of the abutment stress and the distance between the peak abutment stress and the panel were decreased．Due to the extraction of seam 5 # in Tangshan coal mine, the abutment stress in panel Y485 located in seam 9 # was only influenced by the key strata between the two seams．The influence distance of the abutment stress in panel Y485 decreased from 73 m to 38 m, and the distance between the peak abutment stress and the panel decreased from 29 m to 20.5 m．When there is a hard-and-thick key stratum present between two seams, the peak abutment stress is 2.34 times as great as that without one and severe stress concentration is formed during the lower seam extraction after pressure-relief mining.

Water-inrush mechanism and countermeasure for the roof of working face in Zhongguan iron mine

SHI Wenhao，YANG Tianhong，CHANG Hong，WANG Peitao，XIA Dong

2016, 33(3): 403-408.

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Zhongguan iron mine is a water-contained mine attributed to Ordovician Karst water in limestone and it is threatened by water-inrush during the mine construction. In this paper, a water-inrush case at -260 m level has been studied to find out the mechanism based on the combined research of regional tectonic conditions and dynamic monitoring results of the underground water level. The results have shown that the water-inrush is caused by the activation of X1 buried fault and the formation of water-inrush channel. The channel contributes to building the hydraulic connection between the driving face and the aquifer after the fault evolved from water-resisting to water-conducting due to several times of roof coving led by X1 fault exposed in the tension-deformation zone under artificial mining. On the basis of the water-inrush mechanism, the countermeasures summarized as “driving with detection and driving after detection; water plugging taking the first place or with drainage together” for preventing the karst water-inrush at the roof of driving face in -260 m level are established during the mine construction. Thus, construction of tunnels at -260 m level under karst conditions with safety and high proficiency has been achieved.

On preventing the high pressure water-inrush from floor with paste-like backfill mining

QIU Mei，SHI Longqing，YU Xiaoge，GAO Weifu，SHI Yongkui

2016, 33(3): 409-414.

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Studies on the paste-like backfill mining system and the floor failure depth of working faces were carried out in the working face 81006 of Caozhuang coal mine to prevent water inrush from floor karst aquifer. The new type of backfill material made up of cementitious material, coal waste and ash was developed. The backfill mining system was divided into the ground backfilling system and the underground system. The system achieves automatic control of material’s addition, mixing and transportation. Double-block leak hunting in drill was applied to measure the floor failure depth in the backfill mining face (working face 81006) and the mining face by caving method (working face 8812). It turns out that the past-like backfill mining has a significant effect on decreasing floor failure depth caused by mine pressure. Based on the“lower four-zone”theory, we analyzed the reducing mechanism of floor damaged depth caused by underground pressure under the condition of paste-like backfill mining, proving that the paste-like backfill mining is the effective measure to prevent high pressure water-inrush from floor.

Stability control of the roadway group under the influence of overlying goaf

SU Xuegui,，SONG Xuanmin，YUAN Honghu，DU Xianjie

2016, 33(3): 415-422.

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During the downward mining process of close-distance coal seam，affected by the upper coal goaf and pillar, complex changes have occurred in the stress environment and the failure mechanism of the roadway surrounding rock in the lower coal. The stress distribution law, the deformation failure mechanism and stability control of the roadway group in the lower coal were researched through the comprehensive methods of theoretical analysis, numerical simulation and engineering application. The research has shown that：1) The pressure relief effect of overlying goaf led to low stress concentration degree of roadway under goaf and more stable surrounding rock；2) Affected by the pressure transfer of coal pillar, the vertical stress was on a sharp rise with the stress concentration factor reaching 3.84, and large compression-shear failure appeared in two sides and shoulders of the roadway, which eventually led to the whole failure; 3) Roadway in the high stress zone under the coal pillar should adopt the arched section to increase the supporting strength and the anchor prestress; and the cables (bolts) layout in the roadway shoulders to make the supporting system couple with the plastic zone of surrounding rock and both get strengthened. With the optimized support, the roadway roof subsidence is reduced by 42.8%, the actual measured working load of the bolts and cables is reasonably distributed, which realizes the safe and effective control of the roadway of close distance coal seam under coal pillar.

Deformation and failure mechanism and control technology of large section coal roadway subjected to severe mining dynamic load

HE Fulian，ZHANG Guangchao

2016, 33(3): 423-430.

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Sever underground pressure phenomena such as roof caving, sides collapse and support damage frequently occur in the surrounding rocks of coal roadway with fully-mechanized caving during the process of excavation as a result of sever mining dynamic load resulting from large-scale fully-mechanized caving. Those roof and support behaviors have a very bad influence on the safety and transportation of gob-side entry. With Return Airway 20102 in Wangjialing Coalmine as research subject, a combined method of site investigation, theory analysis, numerical simulation and in-situ tests was used to research the mechanism of sever strata behaviors, and the rework technology was put forward. The cause of its failure was summarized as follows: fracture development and low strength, high abutment pressure, large cross-section and unreasonable support. The dynamic process of deformation and failure was concluded as follows: the large-scale fully-mechanized caving leads to the high abutment pressure and the strong storage of stain energy, and the excavation of roadway causes the strain energy released strongly, which leads to severe instability and failure of the roadway; meanwhile the unreasonable support and the large cross-section aggravated the instability and failure. The control principle of excavating and mining was proposed, and the support scheme was determined according to combining geological production. Field practice has shown that after the application of comprehensive control technology, the surrounding rocks of coal roadway remain in a stable state with roof convergences of roadway no more than 136 mm, sides convergences of roadway 116 mm and floor convergences 132 mm.

The application of fuzzy synthesis assessment method to adaptability of gob-side entry retaining in southwest

CAO Shugang，WANG Shuai，FAN Yingchong，YANG Hongyun，CHEN Xianzhe

2016, 33(3): 431-436.

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Gob-side entry retaining has shown great superiority in practical application. In order to promote the gob-side entry retaining technology in small-to-medium-scale coal mines, this paper has used analytic hierarchy process (AHP) and method of fuzzy synthesis assessment to evaluate the adaptability of gob-side entry retaining. According to experts’ experience and experimental results, six geological factors have been set i.e., burial depth, dip angle of coal seam, thickness of coal seam, lithology of roof, influence coefficient of immediate roof thickness, and roof lithology. Through AHP, the judgment matrix is structured and the weight of each factor is determined. For example, the adaptability rank of gob-side entry retaining of a roadway of a coal mine in southwest region is determined to be grade Ⅴ, consistent with the theory based on the experiments, which showed that the model can play a useful role in evaluating the adaptability of gob-side entry retaining.

Experiment and analysis of bearing capability of arched pallet for anchor bolts

ZHENG Yangfa，KANG Hongpu，JU Wenjun，ZHANG Jian，LI Jianbo

2016, 33(3): 437-443.

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For further understanding of the influence of arched structure on steel pallet’s mechanical property, and its bearing applicability when matching with different bolts, two equations of bearing capability relationship of arched pallet was established through elastic mechanics theory and limit equilibrium method analysis of shell structure, in which the five impact parameters were discussed based on support engineering practice．Bearing capability and deformation characteristics of square pallets with different thickness and different arch height were investigated through laboratory loading test．The results have shown that, the pallet bearing capability has a positive growth relationship with its steel plate thickness, proportion of arch height and the bottom circle diameter．Test of bearing capability well verified the correctness of the theoretical relationship, and the size and strength of adjustable ball-pad played a very important role for full bearing capability and support effect of arched pallet．Based on the above studies and the coal industry standard, a reasonable reference table was proposed for matching ordinary anchor bolts specification and different arched pallets’ size, which would have reference value for mines’ support engineering.

Study on asymmetric support of coal roadway nearby narrow pillar based on microcracks evolution process in fully-mechanized caving mining

YIN Shuaifeng，HE Fulian，CHENG Genyin，ZHAO Yongqiang

2016, 33(3): 444-451.

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To solve the controlling problems of the large deformation after the initial tunneling in coal roadway nearby narrow pillar, combined with the basic understanding of dynamic and static abutment pressure, the evolution process of microcracks was researched through CT scanning. Then, the asymmetric support technology of parallel-arranged composed of double truss cables and single cable was put forward, and its composition structure, controlling mechanism and stress field distribution characteristics were researched systematically. The research results have shown that 1) The numbers, development speed and penetration speed of microcracks are asymmetric on both sides of coal roadway; 2) The stress field distribution characteristics in the roof and coal pillar could be described as batwing expansion along vertical direction, and more anchorage-body remains in a compression state in stress superposition areas. The parallel-arranged asymmetric support technology was successfully applied in roadway 120210 nearby narrow pillar. The deformations in the roof and coal sides are coordinated and the controlling effects are well. The research findings will have great theoretical and practical value to other projects with similar engineering geological conditions.

Failure mechanism and support design of deep composite soft rock roadway in Yangcheng coal mine

JIANG Bangyou，WANG Lianguo，GU Shitan，ZHANG Jihua，WANG Rongchao

2016, 33(3): 452-459.

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To solve the control problem in a series of nonlinear rheological large deformation phenomena such as serious floor heaves and section shrinkage of the south limb soft rock roadway in Yangcheng coal mine, the surrounding-rock geomechanical properties and failure characteristics were analyzed with the methods of mechanical testing, theoretical analysis and field test. By establishing roadway mechanical model under biaxial uniform loading, the deformation and failure mechanism of the south limb soft rock roadway were studied and revealed. The results have shown that ground stress environment has a very adverse effect on the soft rock roadway, the surrounding-rock of the roadway is HJS composite soft rock, and the small complete strata thickness owing to joint fissures and loose damages of the surrounding-rock is the key factor for severe failure of the roadway. Based on the complex failure mechanism of the soft rock roadway, the combined supporting was put forward through bolting, metal net, guniting, and grouting with bolting and grouting support as the main method. In addition, a new grouting cable anchor was designed and applied. Deep and shallow coupling grouting was realized by the grouting bolt and the new grouting cable anchor. Finally practical engineering has shown that the combined supporting was effective and the large deformation of soft rock roadway was effectively controlled. The achievement of deformation control of the south limb soft rock roadway in Yangcheng coal mine provided an important reference for the similar roadway project.

Study on quantitative calculation method of mining roadway supporting intensity under depressurized mining

YU Fenghai，ZHAO Tongbin，TAN Yunliang，GUO Weiyao

2016, 33(3): 460-466.

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In order to realize the quantitative supporting intensity of mining roadway under depressurized mining, characteristics of floor stress distribution were discussed, coefficient of depressurized mining was proposed, and the calculation method about supporting intensity of roadway was given in this paper based on theoretical analysis, numerical simulation and field test. The results have shown that the floor zone can be divided into fractured zone (arc), decreased stress zone (parabola), increased stress zone (oval), and original stress zone. Decreased stress zone depth is 60%-70% times the width of coal face, increased stress zone is 3 times the width and 5 times the depth of external stress field length. The range about coefficient of depressurized mining is 0-1.0 and the depth of key influence areas is about 40 m. According to the field monitoring, required supporting strength of gateway decreased for depressurized mining. Although the supporting spacing increases from 600 mm to 800 mm, the roof to floor convergence decreases 46.5%, and the deformation of two roadsides reduces by 46.7%. It is rational determination to consider the effect of depressurized mining for roadway support.

Study on double-roadway layout under section coal pillar of ultra-close upper coal seams in Huojitu mine

CHEN Sushe，ZHU Weibing

2016, 33(3): 467-474.

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The rational layout of mining roadways below upper synchronously mining longwall faces under the condition of ultra-close coal seams is the key issue for the safe operation in Huojitu coal mine. To overcome this critical challenge, this paper studied the double-roadway layout under the upper section coal pillar in less than 2 m interval coal seams through numerical simulation and field measurement．It is showed that when the widths of section coal pillars are 20 m and 35 m, the maximum cover depths of lower double-roadway are 100 m and 150 m, respectively. By placing the double-roadway under the upper 35 m-wide section coal pillar in No.3 panel of Huojitu mine, the deformation of the roadway is only 50 mm totally in spite of 3 times mining influence. The roadways can be in safe and normal use without maintenance. This provides reference for safe and efficient mining under the similar shallow ultra-close coal seams condition.

Width optimization of narrow coal pillar of roadway driving along goaf in fully mechanized top coal caving face

QI Fangkun，ZHOU Yuejin，CAO Zhengzheng，ZHANG Qi，LI Ning

2016, 33(3): 475-480.

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The width of the narrow coal pillar of roadway driving along goaf is the key factor affecting the surrounding stability of the mining roadway in fully mechanized top coal caving face. Based on the abutment pressure distribution characteristics and the ultimate balanced theory, the reasonable width of narrow coal pillar should be chosen between 4.1m and 7.2 m, combined with the engineering condition in workface 3309 of a mine in Shandong. In order to optimize the width of the narrow coal pillar, the effect of plastic area distributions and stress distribution characteristics of the two sides of coal pillar under conditions of different width of narrow coal pillar have been studied by numerical analysis. The optimal width of coal pillar is 5 m. The validity of the optimal coal pillar width was verified by the engineering practice in workface 3309. Field monitoring has indicated that the surrounding rock deformation of the mining roadway could meet the requirements of safety production.

Deformation analysis and neutral plane stability control technology of small coal pillar with gob-side entry

XU Xingliang，LI Junsheng，TIAN Suchuan，LIU Zhongtang，LI Yuewen

2016, 33(3): 481-485.

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According to the abutment pressure distribution of stope lateral coal under the condition of small coal pillar with gob-side entry, some neutral plane areas where the deformation of coal is small in coal pillar have been studied through numerical calculation and in-situ measurements. As the size of coal pillar increases, the width of neutral plane area increases. However, the speeding-up of neutral plane area occupying the width of coal pillar decreases and becomes stable. The research has found that the intensity of bolt support can noticeably increase the width of maximum bearing and bearing ability for neutral plane area. The stability control technology of small coal pillar with full plastic zone was put forward. And the research results were successfully applied to engineering practice.

Elastic stress analysis on circular frozen wall in bi-directional unequal ground stress field under unloading condition

WANG Yong，YANG Weihao

2016, 33(3): 486-493.

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To obtain the stress and deformation of circular frozen wall in bi-directional unequal ground stress field, an elastic mechanical model of frozen wall interacting with surrounding rock has been established with the excavation unloading considered. The analytical solution has been derived and verified by finite element software，which has also been compared with the traditional loading model. The hoop stress and radial displacement distributions in the inner edge of frozen wall have been analyzed emphatically as well as their relationship with different influencing factors. The results have shown that the calculation results of the loading model are overall larger than the unloading model. When the elastic modulus ratio β between frozen wall and surrounding rock has a small value, the consideration of their interaction can decrease the stress and displacement effectively. If the ground stress uniformity coefficient λ is small enough, the tensile hoop stress will appear in the inner edge of frozen wall, which is not conducive to the full play of its carrying capacity. In addition, unloading rate, β, λ, and frozen wall’s radius ratio all have significant impact on the stress and displacement of frozen wall, while the influence of the Poisson’s ratio is relatively small. On the whole, the calculation model in this paper can really reflect the stress and deformation of frozen wall, and the research findings can guide the frozen wall’s design and construction.

Vertical additional force and structure of shaft lining in thick aeolian sand strata

ZHANG Chi，YANG Zhijiang，ZHANG Tao，HAN Tao

2016, 33(3): 494-500.

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Through physical experiment and numerical calculation, the vertical shear test between saturated sand and shaft concrete interface was preliminarily studied, and some interface shear strength parameters were obtained. The variation of vertical additional force on shaft lining in thick aeolian sand strata was further studied through numerical calculation. Research results have shown that 1) The vertical additional force presents nonlinear growth rule as the depth in aeolian sand strata increases, and the maximum vertical additional force appears near the interface between aeolian sand and bedrock; and 2) After entering the bedrock, vertical additional force rapidly decreases because of bedrock force-sharing effect. In more than 100 meters depth of aeolian sand, as water level of aeolian sand aquifer declines (such as decline more than 20 meters), traditional double layer shaft lining can be ruptured near the interface between aeolian sand and bedrock under the action of vertical additional force. Therefore, the compressible shaft lining structure should be adopted to limit the increase of vertical additional force in thick aeolian sand strata.

Mechanical behavior investigation for floor rock stratum in the water-rich coal seam

LI Hailong，BAI Haibo，QIAN Hongwei，MA Dan，XU Jing

2016, 33(3): 501-508.

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One special hydrogeologic phenomenon was found when building well drilling for Xiaojihan mine located in Yulin city, north of Shaanxi province. The coal seam is a main aquifer to the geologic structure of the nearby area. Different tests including rock mineral composition test for floor rock samples, rock expansion test and the rock strength test under water pressure have been applied to find out the mechanical properties of the floor rock stratum under this special hydrogeologic phenomenon. The following conclusions have been drawn: 1) The coal seam of Xiaojihan mine is found out to be a fracture aquifer as well as a main aquifer. The floor rock has been exposed to water erosion for a long time, which makes the rock body easier to be deformed or softened. This will cause a fracture expansion of the floor strata crack and damage the stability of the floor strata. 2) Some dilating mineral such as montmorillonite and illite are determined from the floor rock sample. The dilatability of these minerals can be the micro-influencing factor for the expansion deformation of the sample. 3) Three stages were observed in the rock expansion test of floor rock samples: rapid expansion, slow deformation and the end of deformation. Within 2 hours after the test started, a deformation expansion occupied 73.3% of total expansion was observed. From the third to the 12th hour after the test started, the deformation expansion of this stage occupied 24.7% of total expansion. After 12 hours, no deformation was observed. 4) The compressive strength, elastic modulus and shear strength decreased as the moisture content increased. The relationship was calculated to be exponentially declining. 5) After 12 hours’ under-water test, the compressive strength, elastic modulus and shear strength decreased by 71.6%, 72.3% and 65.4% respectively. It is obvious that coal seam fissure water has significant effect on the erosion and softens of the floor rock.

Experimental study on mechanical properties of mudstone fracture before and after grouting

LIU Quansheng，ZHOU Yueshi，LU Chaobo，ZHANG Jianming

2016, 33(3): 509-514.

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In the present study, the closure behavior and shear strength of mudstone fracture are investigated through direct shear test before and after grouting. Experimental results have shown that 1) The closure deformation of the mudstone fracture decreases by about 49%-57% after grouting; 2) The peak shear strength and residual shear strength can be easily observed; and 3) The shear stiffness of the mudstone fracture increases after grouting. The preliminary reasons for the phenomenon are general due to the increasing contact area caused by the filled material, which can transfer the loading and thus increase the shear strength.

Experimental research on ultrasonic monitoring and forecast methods of rockburst

ZHANG Xiaojun，LONG Kun，SONG Xiuli，ZHENG Huaichang

2016, 33(3): 515-520.

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With the paucity of research on rockburst monitoring，the uniaxial compression test of the rockburst of complete hard rock was carried out with whole-course ultrasonic monitoring. On this basis，failure characteristics and ultrasonic precursor law of rockburst was analyzed and the forecast of rockburst was discussed. The results have shown that the crackling sound produces when the load reaches its peak intensity and then rockburst of complete hard rock occurs. The analysis of sample debris helps find evident splitting phenomenon in the outer region and more serious powder degree of fracture surface and shear phenomenon close to the interior of the specimen, which was the consequence of the strong friction and high energy consumption caused by the increase of internal constraint degree. According to the whole-course ultrasonic monitoring of the rockburst of the complete hard rock, wave velocity develops from stability to fluctuations with the first wave amplitude fluctuating from slightly to violently and the attenuation coefficient from increasing to declining, which can be used as the precursor of rockburst; the first wave amplitude changing from the overall decreasing to significantly increaseing or from continuous decreasing to small fluctuations can also be used as the precursor of rockburst; besides, the process of hard rock specimens rockburst from deformation to damage and fracture and finally burst under load can be reflected by hard rock ultrasonic spectrum.

The influence of bedding angle on acoustic emission characteristics in biotite granulite

YANG Zhenqi，DENG Wenxue，ZHANG Penghai，WANG Peitao，ZHANG Tianwen，YANG Tianhong

2016, 33(3): 521-527.

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In order to study the influence of bedding angles on acoustic emission (AE) characteristics, the AE experiments on the biotite granulite specimens with the bedding angles of 0°, 45° and 90° were conducted. The biotite granulite specimens were taken from Sijiaying open pit mine in Luan County, Hebei province, China. Under the uniaxial compression condition, the spatial and temporal distribution of AE events, the change of the box dimension and the characteristics of the energy release were studied. The research results have shown that：1) The evolution laws of AE events in the specimens with the bedding angles of 0° and 90° were similar, while the evolution laws of AE events in the specimens with the bedding angle of 45° were significantly influenced by the fracture modes; 2) With the increasing of the bedding angles, the number of specimens in which box dimension reduction occurred before the failure was decreasing, and AE energy was prone to releasing in a sudden way. The findings have academic value to the research on revelation of mechanism of disintegration with acoustic emission.

Research on single jointed rock failure mechanism based on mesoscopic characteristics analysis

CHAI Jinfei，GAO Yongtao，WU Shunchuan，ZHOU Yu，GAO Yanhua，GUO Chao

2016, 33(3): 528-534.

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Based on moment tensor theory, P-T diagram method and T-k diagram method, the fracture parameters and their evolution such as spatial position, fracture azimuth, fracture types, stress state and moment magnitude were analyzed to reveal the rock failure mechanism of triaxial compression under the condition of different confining pressure with a large number of acoustic emission (AE) data in the process of generation, propagation and coalescence of cracks simulated by Particle Flow Code. The results have shown that：1) The rock fracture azimuth is influenced by the loading direction and the joint orientation. When the joint orientation and the loading direction are in a certain angle, the principal compressive stress components are gradually distributed around with the joint orientation corresponding location of the P-T diagram. 2) The proportion of linear tension fracture decreases as the angle between joint and Z-axial increases. The proportion of linear shear fracture, mixed fracture and double couple shear fracture increases as the angle between joint and Z-axial increases. 3) The tensile fracture is mainly distributed in the joint plane, and its energy is lower. The shear fracture and mixed fracture type is mainly distributed in the intersecting line of joint plane and free face; and its energy is higher. In conclusion, the rock fracture mechanism and its macroscopic evolution rule can be effective grasped with the moment tensor theory, P-T diagram method and T-k diagram method. These methods provide a new technical measure for the stability analysis of rock mass and its development trend, which is an effective supplement to the traditional analysis method.

Triggered effect of solid tidal stress on rockburst and its mechanism

ZHANG Yuezheng，JI Hongguang，CAI Meifeng，LI Tie，XIANG Peng

2016, 33(3): 535-543.

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There is certain correlation between the occurrence of rockburst and the activity of solid earth tides. In order to further prove triggered effect of solid tidal stress on rockburst, with Huating coalfield as research background, the relationship between rockburst occurring in the roof and the diurnal changes of the tidal has been analyzed through the Schuster inspection method. The results have shown that：1) The solid tidal stress has a significant effect on the occurrence of rockburst. There is a significant correlation between the frequency of rockburst occurrence and the vertical, the horizontal shear stress component of the tidal stress, the value of the P of Schuster inspection is less than that of the triggering threshold value 0.05. 2) The tidal stress has different effects on different levels of rockburst, and with the increase of magnitude, the occurrence of rockburst is controlled by gravity to tectonic stress. 3) For different types of rockbursts, the triggered mechanical function is different. For small and medium-sized rockbursts controlled by gravity, when tidal stress vertical component and the largest minimum horizontal component the rock burst occurs more easily, while the bigger rockbursts controlled by tectonic stress are opposite. 4) The rockburst activities can also cause the distortion of time sequence and shape in the borehole strain in related regional strata.

Numerical study on fracture initiation and propagation of reservoirs subjected to hydraulic perforating

ZHAO Xi，DAI Tao，JU Yang，HU Huifang，YANG Yongming，GONG Wenbo

2016, 33(3): 544-550.

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Understanding hydraulic fracturing initiation and propagation in low permeability reservoir is of great significance for exploiting and enhancing recovery of unconventional oil and gas resources. Cement, mortar and quartz sand were mixed to model the natural shale rock. Our laboratory tests proved that, the mechanical properties, especially fracture toughness, were close to those of the natural shale rock. The numerical codes FRANC 3D and ANSYS were adopted to probe into initiation and propagation of hydraulic fractures in reservoir rock in different horizontal stress ratio and perforation layout. The simulation and analysis have indicated that：1) Perforation fracturing initiation and propagation in three dimensions are properly simulated by FRANC 3D and ANSYS; 2) The initiation fracture pressure decreases with the increase of horizontal stress ratio; 3) Perforation parallel to the maximum horizontal stress has the smallest initiation fracture pressure. Propagation plane deflection tends to be parallel to the maximum horizontal stress when they are not in parallel; 4) Linearly distributed perforation is superior to symmetric perforation and staggered perforation as it provides the minimum initiation fracture pressure.

Pressure measurement technology of drilling borehole down the seam in imitative rock hole

TIAN Shixiang，JIANG Chenglin，SHI Jisheng，PAN Xingfeng，CHEN Yujia

2016, 33(3): 551-556.

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During the measurement of gas pressure in borehole embedded in coal seam, drilling deformation and collapse are very difficult to avoid. In order to fundamentally seal the cracks around borehole in coal seam, gas pressure measurement method conducted in borehole embedded in imitative rock has been put forward in this paper. The mechanical analysis of drilling instability shows that the radius of drilling fracture zone is relevant to rock lithology. Improving the internal friction angle and the cohesion of surrounding rock is an effective way to enhance the strength of rock. Moreover, through mechanism analysis of solidified borehole in coal seam and numerical simulation, it has been found that high pressure grouting technique applied to coal seam can strengthen the intensity of borehole surface. Field comparison tests show that the difference between gas pressure measured in imitative rock borehole and rock borehole is 0.02 MPa and its relative error is only 3.85%. Consequently, gas pressure measurement method in imitative rock borehole is feasible and has a promising future.

Experimental study on the effect of adsorption pore structure on gas emission characteristics

LIN Haifei，CHENG Bo，LI Shugang，XIAO Peng，YAN Min

2016, 33(3): 557-563.

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To reveal the influencing mechanism of adsorption pore structure on gas emission characteristics of coal, with the typical coal samples from Fukang coal mining area of Xinjiang, low temperature nitrogen adsorption experiment and initial velocity of diffusion of coal gas experiment are carried out. The characteristic parameters of adsorption pore and its influence on initial velocity of diffusion of coal gas are studied. The experimental results have shown that：1) The main transition forms of gas diffusion in adsorption pore are the Knudsen and transition; 2) The parameters of adsorption pore have different influences on gas diffusion characteristics: the greater the average pore diameter is, the smaller the gas diffusion resistance is and the greater the initial velocity of diffusion of coal gas is; the greater the specific surface area, volume of pore and each pore size are, the smaller the initial velocity of diffusion of coal gas is; 3) The initial velocity of diffusion of coal gas has negative liner correlation with proportion of micropore and transition pore volume, positive liner relationship with the proportion of mesopore volume, and no obvious relationship with the proportion of specific surface area of each pore size; 4) In the study range, the fractal characteristics of coal pore are significant, the initial velocity of diffusion of coal gas decreases with the linear increase of fractal dimension.

Layout parameter optimization of highly-located drainage roadway along seam for controlling gas with pressure relief from close-distance methane-rich seam group

XIAO Junfeng，FAN Shixing，LU Ping，CHEN Yangyang，CHEN Fu

2016, 33(3): 564-570.

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Highly-located drainage roadway along seam is an important method for controlling pressure-relief gas, whose extraction efficiency is largely influenced by its layout parameters. In order to reasonably determine the relationship between the above two factors, the evolution rule of cracks in roof rocks has been simulated in the mining process of working face 24202 of close-distance methane-rich seam group. Results have shown that the maximum separation fracture zones lie at the point 15 times of the mining height in the vertical direction, and that appropriate broken fissures are 35 m away from the mining boundary along seam, which is the best layout position for highly-located drainage roadway. Therefore, highly-located drainage roadway should be set in the return airway of working face 24202 and, 60 m toward the roof by the dip angle 40°, and 8 m along the seam. Field industrial experiments have indicated that the drainage radius of single highly-located drainage roadway is 55-60 m, 4-5 highly-located drainage roadways are in the active gas drainage period, and total effective drainage distance is about 500 m. In addition, the overall gas drainage amount of highly-located drainage roadway is 25.22 m 3 /min on average, which takes up 60.24% of the total gas drainage in quantity. In summary, high efficiency in controlling of pressure-relief gas was realized.

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