Journal of Mining and Safety Engineering

Fracture evolution characteristics of surrounding rock during ascending mining of closer coal seam in Panyidong coal mine

ZHANG Xiangyang，REN Qihan，TU Min，DOU Yichuan

2016, 33(2): 191-198.

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Based on the special engineering and geology condition of deep coal seam mining in Panyidong coal mine, the characteristics of rock break, crack evolution and subsidence deformation during the ascending mining of deep coal seams were analyzed by physical and numerical simulations in this paper. In addition, the interrelationship between the deformation curve and the layer break, crack development, stress state was further analyzed. The results show that during the mining operation of lower and upper coal seams, the rich cracks areas are mainly located in the right side of coal wall and the left side of open-off cut and above the gob. Rock layers above the gob go through an evolution course with the generating, expanding and closing of cracks. During the lower seam mining, the fractured angle in wall is smaller than that in open-off cut. During the upper seam mining, with the relative location difference of coal faces in the two coal seam, the fractured angle in wall increases firstly, and decreases af- terwards . Moreover, it has close relationship between the curve slope of roof subsidence in different area, the rock crack development condition, and the stress state.

Overlying strata failure process and support resistance determination in large mining height face

YANG Shengli，WANG Zhaohui，KONG Dezhong，CHENG Zhanbo，SONG Gaofeng

2016, 33(2): 199-207.

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Based on the failure control conditions of “intensity parameters-stress environment-weak planes of joints” in coal-rock mass, the failure characteristic of overlying strata in large mining height face was studied, the simulation of failure process was conducted in the laboratory, and the determination of support resistance was theoretically analyzed. The following conclusions can be made: The caving of layers with thin and low strength depends on the scope of abscission layer, the main roof is characterized by the deformation feature of the clamped beam, and the position of fracture line depends on the scope of shear dislocation fracture. Tensile stress shows a continuous distribution type in thin and low strength strata, whereas a non-isolating distribution type is presented in thick and high strength strata. Shear-closed interlaminar fracture develops prior to the face as an inverted trapezoidal form in large scale, whereas tension-open fracture develops inferior to the face as an upward trapezoidal form in small scale. After fracturing, the lower main roof can form single key block structure and the higher main roof can form static three-hinged arch, and the stability of lower main roof is the key of roof control. Determination of the range of immediate roof is put forward according to the condition of single key block structure in lower main roof, the computational formula of roof pressure is deduced based on the principle of conservation of energy, and the influential degree of immediate roof property on each parameter is thus determined: cohesion > plastic modulus> friction.

Top-coal caving process and movement characters of fully mechanized caving face in steeply dipping thick seam

SUN Lihui，JI Hongguang，CAI Zhenyu，ZHANG Biao，YANG Bensheng

2016, 33(2): 208-213.

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To analyze the top-coal caving process and movement characters in steeply dipping thick coal seam face, similar simulations were conducted and fifteen models were constructed according to different top-coal caving interval, top-coal caving sequence, caving methods and dipping, and the influence on recovery ratio and movement law of top-coal and gangue under different caving conditions was comparatively analyzed. The results show that：The combination mode of single sequence top-coal caving from lower to upper in dip direction and one-mining one-caving in the mining direction has the highest recovery ratio, and the recovery ration decreases with coal seam dip increasing. The caving is an non symmetrical cone due to the influence of coal seam dip, a turbination funnel type is presented when caving from upper to lower, whereas a positive conical funnel type is presented when caving from lower to upper. The coal seam dip angle has little effect on the caving funnel. The top-coal retention phenomenon of caving appears from upper to lower, but not appears from lower to upper, thus the lower-end should be caving as much as possible whereas the caving should be controlled on upper-end.

Connected effect between surface subsidence and rock burst in fully mechanized caving face under deep alluvium

WANG Naiguo，ZHU Sitao，WANG Huitao，JIANG Fuxing

2016, 33(2): 214-219.

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According to the rock burst prevention problem of fully mechanized caving face under deep alluvium in Xinjulong coal mine, field research was conducted to study connected effect between surface subsidence and rock burst. The results show that the starting distance of surface subsidence in fully mechanized caving face under deep alluvium is about 114 m, which is merely 1/7 of the mining depth and much lower than the starting distance of mining depth in general mining conditions. When the surface is in the full-mining stage, an obvious connected effect is observed between the surface subsidence velocity and rock burst. When the surface subsidence velocity increases rapidly, the dynamic pressure manifestation can occur strongly in working face, and the rapid increase of surface subsidence velocity is generally ahead of dynamic pressure manifestation. Based on a comprehensive analysis of seismic and surface subsidence data, a certain correlation is verified between the occurrence of rock burst, surface subsidence and strata movement , which can be used as an auxiliary reference for rock burst pre-warning.

Composite effect of key stratum and its influence on strata behaviors

FU Baojie，GAO Mingzhong，TU Min，ZHANG Pingsong

2016, 33(2): 220-225.

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In order to analyze the effect of movement of key neighboring strata on the pressure of longwall mining, and reveal the mechanism of the composite effect of key stratum, failure characteristics of two key neighboring strata and broken law have been studied by using electrical testing technology. And through making the characteristics verified by the pressure data in the test section, the paper has figured out that the stope pressure step is of a big and a small periodical change under the influence of the composite effect of key strata. Thus, the spatial structure model of the type of overlaying strata has been established. According to the structural relationship of key blocks in the model, the support working values of the working faces have been obtained, which have turned out to be in accordance with the measured results, and finally has offered basis of the control of surrounding rock under similar geological conditions.

Failure height of weak overburden by layered fully-mechanized mining in extremely thick coal seam

HAN Jun，ZHANG Hongwei，GAO Zhaoyu，RONG Hai，ZHAO Xiangzhuo，YANG Fawu，WANG Jingxin

2016, 33(2): 226-230.

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To determine the failure characteristics of weak overburden by layered fully-mechanized top coal caving mining, numerical calculation, micro seismic monitoring and transient electromagnetic methods were used in 55003 panel in Laohutai mine to analyze failure height of overburden strata and the relationship between the failure height of overburden and extraction thickness. The results show that the failure height of overburden is linearly related to the extraction thickness under the condition of weak overburden in Fushun mining area, and the failure height of overburden is 8.4 times of extraction thickness. The failure height of overburden with weak layers is smaller than hard overburden in extremely thick coal seam mining. The overburden fracture is mainly controlled by rock structure including oil shale and green shale, and also influenced by F7 fault and F7-1 fault.

Coupled bolt-mesh-anchor supporting technology for deep fault fracture zones throughout layers soft rock roadway

HAO Yuxi，WANG Jiong，WANG Hao，MENG Zhigang，GUO Zhibiao

2016, 33(2): 231-237.

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The mining depth is around 1 000 m in Qishan Mine. With the increase of mining depth, roadway has failure phenomenon including top, side, and floor heave, as well as other large deformation, with a maximum roof and side failure more than 1 100 mm, under the influence of high ground stress, especially horizontal tectonic stress and fault cutting conditions. The existing support can barely control the stability of surrounding rock of roadway, which has seriously affected and restricted the safety production. This paper has presented detailed analysis of the characteristics and controlling factors of roadway failures, based on the supporting project in Qishan soft rock roadway, and has put forward the failure mechanics mechanism of high stress soft rock roadway expansion, and developed the coupled bolt + mesh + anchor supporting measures to realize coupled supports with strength, stiffness and the structure, so as to achieve the stability control in deep soft rock roadway excavation. The effects of this coupling support have already been validated by the results of field monitoring.

Stability of pillars in backfilling mining working face to recover room mining standing pillars

AN Baifu，ZHANG Jixiong，LI Meng，HUANG Peng

2016, 33(2): 238-243.

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To provide theoretical basis to analyze the stability of the surrounding rocks in working face to recover the room mining standing pillars with backfilling, the rock mechanical structure consisting of backfilling materials and pillars has been researched by means of theoretical analysis and mathematical derivation. The results have shown that elastic foundation coefficient of pillars k p , compression ratio of backfilling materials φ, flexural rigidity of roof EI and load of the roof q are the key factors to control the stability of the pillars. Based on the elastic foundation beam theory, the deflection equation of the roof rock beam has been obtained; the calculation of the elastic foundation coefficient of pillars and backfilling materials developed; equations for calculation of the effect of compression ratio of backfill- ing materials on the press on pillars, roof subsidence and characteristics of stress distribution have been deduced; and in the end the assessing formula of pillar stability has been developed in the paper.

Study on roadway damage characteristics and stability control of extra-thick inclined compound roof

SU Xuegui，SONG Xuanmin，LI Haochun，YUAN Honghu，LI Benkui，DU Xianjie

2016, 33(2): 244-252.

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High-angle extra-thick compound roof rock has weak interlayer bonding force and low in-situ strength, and its roadway damage has asymmetric characteristics under the complex stress. Combined with the engineering examples, using similar simulation test, FLAC 3D numerical simulation and engineering test method, the thesis has analyzed the change rule of surrounding rock stress and displacement, etc. of irregular trapezoid and arch roadway, under conditions of conventional symmetric supporting and asymmetric intensive support, and it has also revealed the asymmetric failure mechanism of extra-thick inclined compound roof roadway. It has shown that affected by terrain characteristics, the asymmetric distribution of roadway structure and stress is the primary cause of asymmetric damage of roadway; decreases of compound layered rock level normal binding and stress concentration of obtuse angle parts directly lead to weak shear slip instability; the arched roadway with asymmetric support can effectively improve the stress state of surrounding rock, so as to reduce the deformation of the surrounding rocks,improve the stress state and balance load capacity of surrounding rock supporting system．

Deformation characteristics and control technology of roadways in soft steeply inclined coal seam

MA Zhenqian，JIANG Yaodong，YANG Yingming，ZHANG Kexue，MA Zhisheng，CAI Laisheng

2016, 33(2): 253-259.

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In order to solve the roadway support problem in soft steeply inclined coal seam, numerical calculation method has been used to study the roadway stress and displacement distribution characteristics in steeply inclined coal seam. The results have shown that the natural balanced arch formed at the top of roadway after excavation gradually extends upward along the inclined plane of coal seam, which is similar to the distribution form of vertical stress. The key supporting parts of the roadway are top coal and coal side. Based on the above research, a comprehensive support system with bolts, steel strips, nets, anchor cables and high strength arch beams has been proposed, aiming at fully mobilizing self-bearing capacity of surrounding rock to form a whole bearing system with the support system. Field test results have shown that the support system can effectively control the roadway stability, and the wall-to-wall relative displacement is less than 40 mm, which may also provide some reference to the roadway support in similar conditions of steeply inclined coal seams.

Stability analysis and engineering application of TBM deep coal mine roadway and surrounding rock

TANG Bin，CHENG Hua,，YAO Zhishu，WANG Xiaojian

2016, 33(2): 260-264.

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Aiming at practice of the first shaft coal mine TBM, the roadway surround rock stability analysis and informative monitoring have been carried out. The distribution law of displacement, stress and plastic zone have also been studied and the stability of support design has been verified by ABAQUS finite element numerical software. Results have indicated that the maximum deformation on the roof is 33.26 mm and the range of plastic zone is 0.8-1.2 m. The supporting way has been chosen as the mode of bolt support. Fracture developing condition inside surrounding rock, roadway convergence and deformation and bolt stress have all been measured and the results have illustrated that crush zone ranger reaches up to 1.5 m over roof, the maximum horizontal convergence is 12 mm, and that bolt stress ranges from 43.1 to 65.1 kN. The maximum penetration rate of TBM is 404 m per month which is 5-10 times that of conventional drilling and blasting or roadheader, and the TBM excavation has also been proved to be safety and efficient according to engineering application.

Study of instability mechanism and control of roadway regenerated roof in random joint rock

WANG Tongxu，MA Wenqiang，QU Kongdian

2016, 33(2): 265-270.

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To study the instability mechanism and control method of roadway regenerated roof in random joint rock, a random joint simulation program has been written to build a random joint numerical roadway model through FISH language embedded in UDEC software, combined with the Monte-Carlo simulation method and based on statistical result of joint parameters in an excavation roadway of Beizao coal mine. The stability failure process and support form of roadway regenerated roof has been simulated in the model, and the numerical simulation result has been tested by engineering application. The research has shown that some small rock blocks in the support roof are easy to slide and to be caved, then key rock block slides down along the joint interface, and when one end of key rock block is separated from the roadway wall, the whole roof loses its stability and begins to collapse. The proper roadway support form under regenerated roof is the combination of cable anchor and shield support, which can control the roof deformation and prevent the caving of broken small rock blocks.

Study on identification along with drilling of roof strata of excavation roadway

CHEN Jiasheng，DENG Haishun，GAO Mingzhong，CHENG Yunhai，WANG Chuanli

2016, 33(2): 271-277.

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In order to identify roof strata in the process of excavation, a measurement method used to detect roof strata by means of pressure and quantity of flow in hydraulic system of bolter has been presented. Calculation formulas of drilling parameters have been deduced. Test system has been built to detect roof strata along with drilling. Drilling data have been compared and analyzed with uniaxial compressive strength (UCS). The research results have shown that: 1) It can be inferred that drills bit has passed though rock interface or weak interlayer accordingly while a step or pulse change of pressure and flow in hydraulic system of bolter has been detected. 2) Tests have measured that the ratio of maximum and minimum value of penetration rate is 12.4 when drills bit passing through weak interlayer, which has shown that penetration speed is the most sensitive one among several drilling parameters. 3) Strata strengths and position of roof strata can be calculated by detecting pressure and flow in hydraulic system of bolter.

Instability mechanism of dynamic pressure roadway and staggered distance optimization in nearby-layer simultaneous working faces

MA Haifeng，YIN Zhiqiang，GUO Feng，LI Chuanming，LI Jiazhuo

2016, 33(2): 278-283.

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Aiming at the large deformation problems of roadway in nearby-layer simultaneous working faces, the paper has studied different staggered distances along strike and tendency in nearby-layer simultaneous working faces by means of theoretical analysis, numerical simulation and field measurement. The results have shown that：1) Owing to the impact of multiple mining during the progress of simultaneous mining, strata between the upper and lower working faces have experienced the continuous-quasi continuous-discontinuous-dispersion process. 2) Under the different strike staggered distances, the peak of abutment pressure, the scope and degree of failure rock have changed in descending order from staggered distance of 20 m, 0 m, 50 m to 60 m. 3) Affected by multiple mining, the displacement of haulage roadway in the lower face has shown stepped increase with the approach of working face, and twice experienced the process of gradually increasing-obviously increasing and being stable. Multiple mining effects which have been produced by simultaneous mining should be taken into considera- tion in the mining area design, and reasonable strike staggered distance and tendency staggered distance should be designed and optimized to improve the mechanics state of the stope rock, especially surrounding rock of roadway.

Deconstruction and stability calculation of pillar structure body

CHEN Qingfa，NIU Wenjing

2016, 33(2): 284-289.

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The fundamental concepts of pillar model and pillar structure body were defined in this paper. Based on the survey data of structural planes of the roadways related to the selected area of pillar model, the block calculation function of GeneralBlock was used to preliminarily deconstruct the pillar structure bodies. According to the authenticity analysis results of pillar structure bodies, the spatial endowment situation of pillar structure bodies was accurately deconstructed by using geometric method. Based on the failure modes of structural body, the mechanical model was built and the area of the minimum fixed surface of the fixed structural body was calculated. The mobility mechanisms of the real pillar structure bodies were analyzed by using mechanics and collection methods, and the calculation formula of stability coefficient of the structure body was derived.

Monitoring and analysis of hydration heat temperature field for high performance mass concrete freezing shaft lining

ZHANG Tao，YANG Weihao，CHEN Guohua，HUANG Jiahui，HAN Tao，ZHANG Chi

2016, 33(2): 290-296.

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The development law of hydration heat temperature field for high performance mass concrete freezing shaft lining is very important for the study on shaft temperature stress and key to improve the quality of shaft wall lining. In order to obtain the measured data, the early age temperature field of freezing shaft lining concrete, which has the largest shaft diameter and thickness in the domestic, has been monitored and analyzed. 4 monitoring layers have been set up. Through the real-time monitoring, the research has obtained the temperature field distribution rules and radial temperature rise laws, for high performance concrete freezing shaft lining whose strength up to C60 and thickness to 2.5 m by one-time pouring. For different strength and thickness of shaft, the maximum temperature has reached 61.4-73.1 ℃, and the maximum temperature rise has reached 39.6-48.8 ℃, and the maximum internal temperature difference has run up to 24.3-33.0 ℃. Double exponential relation has been obtained, which fits the maximum temperature rise and age of cast-in-place concrete shaft. Combined with the engineering practice. Besides, the technical measures taken to prevent the crack of mass concrete shaft from aspects of concrete materials, temperature rise of hydration heat, constraints reduction and curing conditions. The measured data have provided valuable basic information for the design and construction of freeze shaft, and provided reference for construction of mining.

Analysis of temperature field for multi-circle-pipe freezing considering variability of soil parameters

WANG Tao，ZHOU Guoqing，YIN Qixiang，XIA Lijiang，LIU Yuyi

2016, 33(2): 297-304.

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In order to further investigate the effect of spatial variability of soil parameters on the temperature field of multi-circle-pipe freezing, this paper has proposed a method to calculate the plane average variance from just the point variance by simulating heat transfer coefficient, specific heat capacity and latent heat of phase transition as spatially random fields, and by means of the local average theory of random field. Based on Neumann stochastic finite element method, the stochastic finite element calculation program has been independently developed to figure out the distribution law of temperature field of multi-circle-pipe freezing. The results have shown that the random field and the local average theory can consider the variability of soil parameters reasonably. The two-dimensional triangular local average method can perfectly be combined with triangular finite element method, and the corresponding relation is clearer, and the program is simpler to compile. The randomness of soil parameters results in the randomness of temperature field. In this paper, the mean temperature and the average thickness of stable frozen wall are -22.6 ℃ and 10.5 m. Both of their variable coefficients are 0.224. The mean temperature of shaft-lining is -12.8 ℃ and its standard deviation is 2.4 ℃.

The process and countermeasures for ecological damage and restoration in coal mining area with super-size mining face at aeolian sandy site

BIAN Zhengfu，LEI Shaogang，LIU Hui，DENG Kazhong

2016, 33(2): 305-310.

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Fragile ecological environment and strong mining intensity are the distinctive characteristics of the super-size mining face at aeolian sandy area. Thus, the ecological and environmental damages induced in aeolian sandy area are quite different from that in Eastern China. The environmental damage process has been divided into four stages in this paper: strata failure, ground subsidence, habitat change of the animal and vegetation, and succession of the ecology system at the mining area. The formation and changing rule of ground fissures, distribution soil moisture, changes of groundwater, and plant spe- cies diversity & coverage under the impacts of underground coal mining have been analyzed. Finally, the paper has put forward the idea that the countermeasures for the ecological restoration at aeolian sandy area should not only focus on ecology protection but also remediation, taking both different damage conditions of the environmental factors and objectives of the ecological restoration into ac- count.

Study on water inrush prevention technology by pre-grouting in surrounding rock of roadway

CAO Shenggen，CHENG Zhenggang，ZHANG Yun，JIANG Haijun，WANG Chen

2016, 33(2): 311-317.

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The geological data of Jiaozuo mining area and Zhongmacun colliery has been investigated and sorted out to analyze the sources and conduits of water bursting; the constitutive relation of surrounding rock in water inrush area has been raised according to rock and soil effective stress principle, besides the study has shown that the method of water inrush prevention is to increase the effective stress of surrounding rock and decrease the pore water pressure simultaneously. And the rheological property, flowing law and coverage pattern of grout has been analyzed and researched deeply; then in allusion to the actual conditions of Zhongmacun colliery, a technology of water inrush prevention by pre-grouting in surrounding rock of roadway has been designed and the grouting parameters have been determined. The final project practice has demonstrated the reasonability of the design and has obtained good water plugging effect and successfully met the needs of the mine safety production.

Experimental study on mining-induced failure depth lagging coal wall secondary deepening rule

LI Hailong，BAI Haibo，MA Dan，XU Jing，QIAN Hongwei，TIAN Chen dong

2016, 33(2): 318-323.

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The paper has firstly clearly detected and put forward the view of mining-induced failure depth lagging coal wall secondary deepening rule. Moreover, Jincheng, Yulin, Ordos coal mining working faces have been chosen to verify the point of view. By using better field test conditions water injection test and floor rock strain continuity of detection have been implemented to the floor damage rule after the coal wall pushing. The detection results have shown that: 1) Floor rock damage has occurred in the area of stress concentration when the working face is just pushed through the measuring point for the first time. 2) The working face has been 15 m to 20 m pushed away from point. After that point in the first periodic pressure, water-conductive failure depth of measuring point position has appeared secondary lagging deepening, and the degree of damage deepening is 1-2 m. 3) When the working face has been pushed away from point after 2-4 periodic pressure, the deformation state of floor rock in measuring point position tends to be stable. 4) When the working face has been pushed away from measuring point between the 1st periodic pressure and 4th periodic pressure (the working face pushed away from point 15 m to 60 m), the distance is the high-risk areas for backplane lagging water-inrush. 5) Results of bottom water injection test and detection of rock strain detection test are of high consistency.

Calculation of hydraulic conductivity in high water-pressure test

LIANG Dexian，JIANG Zhenquan，CAO Dingtao

2016, 33(2): 324-328.

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Based on turbulent flow and non-Darcy flow, the hydraulic conductivity calculating formula was derived by using hydraulic pressure in water injection borehole, length of the water injection part, hydraulic pressure and discharge in monitor borehole. With the test results of coal seam floor’s water-pressure in a mine, the difference of hydraulic conductivities under different flow status were analyzed, and it shows that the calculating result of hydraulic conductivity is greatly influenced by flow patterns, and the rock masses’ permeability can be changed greatly by hydraulic pressure. The paper provides an effective method for calculation of non-Darcy flow hydraulic conductivity in fracture rocks under turbulent flow conditions.

Experimental study of impact of deformation history on water-sand seepage characteristics of broken rock

CHEN Jiarui，PU Hai，XIAO Cheng，LIU Guihong

2016, 33(2): 329-335.

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In order to study the impact of deformation history of broken rock on the water-sand seepage characteristics, a set of water and sand permeable system has been designed. The permeability test of distribution diameter rock fragmentation in MTS816 series of electro-hydraulic servo controlled rock mechanical test machine has been conducted under two different deformation experience. The results have shown that the broken rock deformation experience has no obvious effect on the water seepage characteristics. In addition, when the broken rock porosity is within a certain range, the porosity will reduce due to sand filtering effect and result in permeability reduction in the water and seepage process. And broken rock with creep history are easier to filter the sand in the water and seepage process. Sand filtering quality are relatively more, and sand inrush quality are less. When the initial porosity of broken rock are the same, the increase of hydraulic gradient can lead to decrease of sand filtering and increase of sand inrush. An expression to describe the comprehensive influence of the initial porosity of broken rock and hydraulic gradient on the amount of sand filter has bee given in the paper, which supports the risk prediction and assessment of water bursting and sand inrush of broken rock.

Single-bucket excavator overcast stripping technology in narrow cut zone

CHEN Shuzhao，CAI Qingxiang，LIU Fuming，SHANG Tao

2016, 33(2): 336-341.

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Aiming at problems like large investment and poor adaptability of overcast stripping system of dragline, a stripping system suitable for thin and medium thickness seam mining has been put forward. The excavator has overcast the overburden in order to expose the coal seam roof, and the hydraulic backhoe standing on the platform for secondary pouring pile has been used to expose the coal seam bench slope, and finally to finish the overcast stripping. Compared with the shovel-truck system, the overcasting technology system can not only avoid the high cost of truck transportation, but also shorten the distance of open-pit stripping. Therefore, even the repeated overcast rate is up to 100%, using the overcast stripping system is still reasonable economically. The case study has shown that, using overcast stripping in Anjialing open-pit coal mine for 11 # coal seam mining can save the cost about 14,000,000 yuan/a.

Experimental study on compaction and fractal characteristics of saturated broken rocks with different initial gradations

YU Bangyong，CHEN Zhanqing，WU Jiangyu

2016, 33(2): 342-347.

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Using the MTS816.03 test system and self-designed compression apparatus for broken rocks, the compaction tests for saturated broken rocks with different lithologic have been conducted, and the influence of lithology, axial stress, initial gradations and loading rate on compaction deformation and fractal characteristics has been analyzed. The results have shown that：1) The compaction processes of gangue, mudstone and sandstone are similar and can be divided into two stages, including the rapid compaction deformation stage (0-4 MPa) and the slow compaction deformation stage (after 4 MPa). However, the compaction deformation rate of limestone is steady. 2) Under the same initial gradation, as axial stress increases, the fractal dimension of sandstone samples increases monotonously, and the breaking degree gets higher. The relations between fractal dimension and axial stress can be described by exponential function. 3) In the compacting process, as the Talbol exponent increases, the axial displacement increases. As the loading rate increases, the axial displacement decreases. 4) Under the same axial stress, 12 MPa, as the Talbol exponent increases, the increment of fractal dimension increases and the quantity of rock particles crushed increases. As the loading rate increases, the fractal dimension decreases, and the breaking degree gets lower.

Experimental study on creep macroscopic hardening of filling paste

CHEN Shaojie，ZHU Yan，WANG Qifeng，LIU Xiaoyan，CAO Fengwei，YIN Dawei

2016, 33(2): 348-353.

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To study the long-term strength characteristics of filling paste in coal mine, the uniaxial compression experiments and creep experiments of filling paste specimens have been performed. The weight ratio of cement, fly ash to coal gangue has been 1∶4∶6 in those specimens. The physical characteristics, instantaneous deformation modulus and other features of filling paste specimens have been analyzed based on the experimental results. The results have shown that filling paste has poor density and strong compressibility, and the internal structure of filling paste becomes homogeneous and dense during the slow loading process. Under each stress level of creep experiments, the instantaneous deformation modulus of filling paste increases gradually with the enhancements of stress and deformation before the failure of specimens, and the growth rate is 1.77×10 5 %. At the same time, the strain rates in elastic strain stage decrease gradually. The results have also indicated that the creep strength is higher than uniaxial compressive strength, the average creep coefficient is 1.09, and that the macroscopic strength hardening has occurred in creep experiment.

Experiments on the characteristics of thrust fault activation influenced by mining operation

ZHAO Shankun

2016, 33(2): 354-360.

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With the background of F16 large thrust fault in Yima mining area, a similar model was built based on the geological drilling data and underground exposed structure from five coal mines influenced by the fault. Considering the fractal characteristics and occurrence of overburden on both sides of fault surface, the overburden movement, mine pressure behavior law and dynamic response before and after fault activation were studied by monitoring acoustic emission (AE), overlying strata displacement and stress in mining area. The results demonstrate that the overburden movement, mine pressure and dynamic response show a great difference before and after fault activation influenced by the complicated overburden occurrence structure and the tectonic movement. Before fault activation, the “three zone” of overburden is obvious, and the floor stress is hardly affected by mining and the AE signal is weak. In the fault influential area, the roof abscission layer increases immensely, the fault activation is triggered by mining stress, the floor stress reached the maximum, and the total number of AE events and energy release rate grows abruptly. After crossing a certain distance from the fault, the buckling failure of mining face and the floor stress increase with the increasing length of cantilever rock beam. When bearing stress is released by the caving of antilever rock beam, the floor stress decreases, and the “short block voussoir beam” above the workface cuts down and slides along the fault plane with enormous AE events.

Influential range assessment of dynamic pressure in fault zone with broken rock masses

LAI Xingping，ZHENG Jianwei，JIANG Xinjun，CHANG Bo，SHAN Pengfei，LIU Biao

2016, 33(2): 361-366.

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Surrounding rock of roadway here is deformed easily in fault regions. With coal excavation, concentrated stress formed before working face will cause movement or activation of faults, so that it can lead to a dynamic disaster. In response to the determination of the influential range of dynamic pressure in coal-rock fractured fault zone, taking the specific condition of No.1193 working face in Tunbao mine as the field research object. Combined with hybrid analyses, including mechanism analysis and field measurement, the stress distribution parameter inside the surrounding rock is collected through laying the stress detector and anchor bolt in the rib. It can be concluded that the scope of dynamic pressure within the stope is about 34 m, with the peak dynamic pressure occurring at 5 m before the working face. The assessment of the dynamic pressure can optimize the design of supporting reasonably and ensure the safety of the No.1193 working face in Tunbao colliery.

Energy evolution law of rocks in process of unloading failure under different paths

DAI Bing，ZHAO Guoyan，YANG Chen，DONG Longjun

2016, 33(2): 367-374.

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Based on rock energy change theory and tests under three different pressure unloading paths of rocks, the evolution features and rates of absorbing strain energy for compression, the expanding strain energy for circumferential deformation, the elastic strain energy and dissipated energy have been researched. It has been found that during unloading, the absorbing strain energy for compression has mainly turned into expending strain energy for circumferential deformation in three unloading paths, and the expansion degree is path Ⅲ> path I> path II. The quantity of strain energy dissipation can be significantly increased only near the peak. The initial confining pressure’s influence on absorbing strain energy for axial compression, expending strain energy for circumferential deformation and elastic strain energy is significantly higher than that on unloading path, and the three kinds of strain energy are linearly increased as initial confining pressure increases. Under the same initial confining pressure, elastic strain energy stored near the peak size is of the degree of path II> path I> path III, which can draw a conclusion that path II is most likely to have rock burst if there is rock failure. The unloading path and initial confining pressure have significant influence on energy dissipation. Strain evolution rate in three paths all increases with the increase of initial confining pressure, and the effects of the initial confining pressure on the evolution rate of strain energy is in connection with the unloading path.

Experimental research on failure and energy dissipation law of coal under impact load

ZHANG Wenqing，SHI Biming，MU Chaomin

2016, 33(2): 375-380.

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In order to explore the failure characteristics and energy dissipation law of coal during the impact process, the impact compression test of coal under different strain rates has been carried out by using split-Hopkinson pressure bar (SHPB) of 75 mm in diameter．The influence of loading rate on the energy dissipation and fragment distribution has also been discussed．The experiment results have shown that, the strain rate and energy of stress wave are increasing linearly with the improvement of the bullet velocity．Meanwhile, the dissipation energy which leads to the coal broken is increasing exponentially with strain rate．According to the research on fractal dimension of coal fragment, it has been found that the greater the strain rate is, the larger the fractal dimension is, the smaller the fragment-size is, the more severe fragmentation is. The relationship between fractal dimension and strain rate and dissipated energy density is of logarithmic growth, which means the increasing trend of fractal dimension is getting slower.

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