Estimation of Crack Initiation and Propagation Thresholds of Confined Brittle Coal Specimens Based on Energy Dissipation Theory

Ning, Jianguo; Wang, Jun; Jiang, Jinquan; Hu, Shengmin; Jiang, Lishuai; Liu, Xuesheng

doi:10.1007/s00603-017-1317-9

Cited by 130 publications

(46 citation statements)

References 34 publications

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“…Suppose c3 = 11MN/m, with respect to 2 = 7MN/m and c3 =8.6, 8.3, and 8 m 2 = 7MN/m and according to (5), (7), and (10), the support pressure curve 4 ( ) (x is the [8,10] m section) for the hardened zone of coal seam when 4 =8 m and c4 =2 m and the support pressure curve 3 ( ) (x is the [10,18] m section) for the softened zone of coal seam when 3 = 10m and c3 =8.6, 8.3, and 8 m were plotted by Matlab, as shown by curves 1, 2, and 3 in Figure 7. A horizontal tangent line is located at 3 = 10m on the support pressure curves.…”

Section: Expressions Of Support Pressures In Softened and Hardenedmentioning

confidence: 99%

“…For a hard roof with advanced fracture, when the working face advances to below the roof fracture line, if the supporting resistance of frame and friction between seams are insufficient, the roof easily subsides in a stepped style, causing collapse accidents under pressure and even rock burst disasters. Many studies have been conducted on the deformation, law of motion, and fracture of a hard roof under the overlying load by field observation, similar material simulation, numerical simulation, and theoretical analysis [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Qian et al [15,16], Miao et al [17], and Li et al [18] analyzed a hard roof by assuming the support pressure relationship between coal seam and immediate roof as an elastic foundation and obtained some basic results such as the deflection solution for a hard roof and the maximum bending moment in the front of a coal wall and for an advanced roof fracture.…”

Section: Introductionmentioning

confidence: 99%

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Bending Moment Characteristics of Hard Roof before First Breaking of Roof Beam Considering Coal Seam Hardening

Jiang

Pan

et al. 2018

Shock and Vibration

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The mechanical properties of a coal seam affect the distribution of support pressure. Considering the strain hardening effect of coal seam, the support pressure relationship of three zones-softened, hardened, and elastic-of a coal seam with regard to a hard roof is proposed, and methods to determine an approximate expression for the support pressure of hardened zone of coal seam, the range of hardened zone, and the corresponding peak values of support pressure are provided. The deflection equations of a hard roof under three different support pressure relationships of coal seam before the first breaking were theoretically derived, and all the relevant integration constants were determined. Numerical examples of two cases are provided for calculating the bending moment of a hard roof and the support pressure of a coal seam. The analysis shows that as the working face advances, the maximum support pressure increases, the residual strength of coal seam at coal wall decreases, the overall deflection of roof gradually increases, the maximum bending moment of roof in the front of coal wall increases, and the advanced distance of roof bending moment peak gradually increases. As the depth of softened zone of coal seam increases, the similar conclusion is obtained, and the advanced distance of the roof bending moment peak increases at a relatively fast speed. Because the bending moment peak of hard roof is located near the support pressure peak in the softened zone of coal seam, the depth of softened zone of coal seam significantly affects the advanced distance of the bending moment peak of a roof. The actual advanced fracture distances of hard roof are distributed in a relatively broad range. The results indicate that there is a "large and long" type advanced fracture distance occurring in the actual stope. With the same overlying load and stope parameter conditions, the maximum support pressures of support roof in softened, hardened, and elastic zones considering a hardened coal seam are smaller than those in softened and elastic zones without hardening. However, the plumpness in front of the peak of the former support pressure curve is superior to that of the latter, and both the bending moment peak value and the advanced distance of bending moment peak of the former are higher than those of the latter.

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Section: Expressions Of Support Pressures In Softened and Hardenedmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bending Moment Characteristics of Hard Roof before First Breaking of Roof Beam Considering Coal Seam Hardening

Jiang

Pan

et al. 2018

Shock and Vibration

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“…Numerous studies have been performed using different methods to estimate the energy evolution due to excavation . Some researchers have analyzed the energy change with in situ investigations based on feedback analysis of acoustic emissions and microseismic and stresses .…”

Section: Introductionmentioning

confidence: 99%

“…Numerous studies have been performed using different methods to estimate the energy evolution due to excavation. [10][11][12][13] Some researchers have analyzed the energy change with in situ investigations based on feedback analysis of acoustic emissions and microseismic and stresses. [14][15][16] Their results indicate that energy changes due to excavation are associated with in situ stress, geological and geotechnical conditions.…”

Section: Introductionmentioning

confidence: 99%

A numerical study of the mining‐induced energy redistribution in a coal seam adjacent to an extracted coal panel during longwall face mining: A case study

Wang

Qiu

Ning

et al. 2019

Energy Science & Engineering

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Mining of the coal seam adjacent to the extracted coal panel is widely practiced in China to improve coal resource recovery rates, but the energy change associated with longwall mining may present a new risk to ground stability and gateroad failure. To understand the energy change effectively, a meticulously validated numerical model, built using FLAC3D software, incorporating a double‐yield model for the gob materials and a strain‐softening model for the coal/rock masses, was developed to investigate the energy redistribution in coal seams and barrier pillars during the process of mining the coal seam adjacent to the extracted coal panel. The model results showed that the closer the region was to the LW 5301 gob, the higher the location and magnitude of the peak strain energy density. Consequently, the risk of rockburst in coal seams was greater than that in barrier pillars. Along the coal seam strike, with increasing advancing distance from the setup room, the magnitude of the peak strain energy density gradually increased to 1.88‐2.78 times the premining energy level. In addition, along the coal seam dip, the maximum distance from the peak strain energy density to the edge of the coal seam was approximately 16‐28 m, which is greater than that in the barrier pillar. The proposed numerical simulation procedure and calibrated method could be a viable alternative approach to evaluate longwall mining‐induced energy changes.

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“…They found that confining pressure had a significant influence on the cyclic dynamic deformation and fatigue damage evolution, and with increasing confining pressure, the axial strain at failure increased as did the residual volumetric strain at the initiation of dilatancy. Ning et al 21 experimentally investigated the stress-strain relations and energy evolution characteristics of coal samples under cyclic loading-unloading triaxial compression and introduced a new energy-dissipation method to identify crack initiation and propagation thresholds. Zuo et al 18,19 analyzed the failure behavior and axial crack recovery effect of coal-rock combination bodies under different stress levels of cyclic loading-unloading.…”

mentioning

confidence: 99%

Experimental study on evolution in the characteristics of permeability, deformation, and energy of coal containing gas under triaxial cyclic loading‐unloading

Chu

Sun

Zhang

2019

Energy Science & Engineering

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To further more deeply understand the influence of cyclic loading‐unloading on coal seams during mining and reduce the rock burst and coal and gas outburst disasters and ensure safety during coal mining, triaxial cyclic loading‐unloading tests were performed on coal samples. The permeability recovery rate, residual deformation, and dissipated energy ratio were defined to analyze the evolution in the characteristics of permeability, deformation, and energy observed during the triaxial cyclic loading‐unloading test. The results show as following: (a) The absolute permeability recovery rate first gradually decreases and then increases before failure, while the relative permeability recovery rate decreases sharply during the compaction stage, remains stable during the elastic phase, and gradually increases before failure; (b) The cumulative residual deformation increases with increase number of cyclic loading‐unloading, while relative residual deformation first decreases gradually, then stabilities, and then rises sharply before failure; (c) With increases in deviatoric stress, the total energy of coal samples increased as an exponential function. The dissipated energy ratio gradually decreased in the initial stages of cyclic loading‐unloading, then tended to stabilize in the elastic stage and then increase gradually before failure. This study provides precursor conditions for the early warning of rock burst and coal and gas outburst disasters, which has great importance for reducing coal mine dynamics disasters.

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Estimation of Crack Initiation and Propagation Thresholds of Confined Brittle Coal Specimens Based on Energy Dissipation Theory

Cited by 130 publications

References 34 publications

Bending Moment Characteristics of Hard Roof before First Breaking of Roof Beam Considering Coal Seam Hardening

Bending Moment Characteristics of Hard Roof before First Breaking of Roof Beam Considering Coal Seam Hardening

A numerical study of the mining‐induced energy redistribution in a coal seam adjacent to an extracted coal panel during longwall face mining: A case study

Experimental study on evolution in the characteristics of permeability, deformation, and energy of coal containing gas under triaxial cyclic loading‐unloading

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