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Cai W.,China University of Mining and Technology | Cai W.,Key Laboratory of Deep Coal Resource Mining CUMT | Dou L.-M.,China University of Mining and Technology | Li Z.-L.,China University of Mining and Technology | And 4 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014

As the depth and intensity of coal mining increase, rockbursts have been common security issues in coal mines. For solving the difficult problem of the spatio-temporal forecasting of rock bursts, the method of the spatio-temporal forecasting for rock bursts was further developed using microseismic multidimensional information (MMI). First, the index system of MMI identification was established, including the preferred index about the frequency and the proposed indexes about the hypocenter concentration,the maximum and total equivalent stresses. Secondly, the temporal sequence curves and the spatial contour nephograms of each index were obtained based on the normalization method, the classification scriteria of anomaly, and the spatially and temporally statistical smoothed model. Moreover, the score method of R-value was adopted to evaluate and verify the forecasting efficiency of each index, and further determine the weights for each index.Finally,using the method of comprehensive anomaly index, the dangerous state, the specific hazardous areas and levels of rock burst were quantitatively analyzed in real time for the monitoring area. A forecasting example shows that this method has considered the microseismic time-space-strength factor, and played a better prediction on the rock burst.Specifically, it can quantitatively describe the dangerous state of rock burst for the monitoring area in time; reflect the hazardous areas and levels of rock burst in space; and guide the implementation of the measures to control rock burst in the field.Therefore, this study can, to some degree, solve the blindness in implementing the measures to control rock burst, and further develop the approach to monitor and forecast rock burst in space and time.


Chong Z.,China University of Mining and Technology | Chong Z.,Key Laboratory of Deep Coal Resource Mining CUMT | Li X.,China University of Mining and Technology | Li X.,Key Laboratory of Deep Coal Resource Mining CUMT | And 5 more authors.
Arabian Journal of Geosciences | Year: 2016

Particle flow code (PFC2D) software was adopted to investigate the anchorage behaviour and the characteristics of crack initiation, propagation and coalescence of reinforced specimens containing a single fissure (RSCSF). The microscopic parameters of the specimens in the numerical simulation were first validated by experimental outcomes of intact specimens, while the microscopic parameters of the rock bolts were validated based on the results of the RSCSF tests. Then, the mechanical parameters as well as the failure modes in the physical experiments were compared with those derived by the numerical simulation; the results showed good agreement between the simulated macroscopic mechanical properties and failure modes and those obtained in the laboratory experiments. The peak strength, number of cracks and the failure mode varied considerably as the anchorage angle α and fissure angle β increased. Three types of stress–strain curves, types I to III, were obtained from the RSCSF. Shear cracks were observed for all three categories of curves, but the tensile cracks were dominant. The number of cracks and the rate of bond failures decreased as the curve changed from type II to type I to type III. RSCSF failure can be classified into three failure modes: (1) tip crack propagation mode, (2) midpoint crack propagation mode and (3) rock bolt crack propagation mode. These failure modes are primarily differentiated by relations between α and β, and the ratio UCSS/UCSI between the uniaxial compressive strength (UCS, σmax) of the RSCSF (UCSS) and the uniaxial compressive strength of the intact specimen (UCSI). © 2016, Saudi Society for Geosciences.


Li X.,China University of Mining and Technology | Li X.,Key Laboratory of Deep Coal Resource Mining CUMT | Ju M.,China University of Mining and Technology | Ju M.,Key Laboratory of Deep Coal Resource Mining CUMT | And 6 more authors.
Rock Mechanics and Rock Engineering | Year: 2015

Generation, propagation, and coalescence of the shear and tensile cracks in the gob-side filling wall are significantly affected by the location of the fracture of the critical rock block. The Universal Discrete Element Code software was used to investigate crack evolution characteristics in a gob-side filling wall and the parameter calibration process for various strata and the filling wall was clearly illustrated. The cracks in both the filling wall and the coal wall propagate inward in a V-shape pattern with dominant shear cracks generated initially. As the distance between the fracture and the filling wall decreases, the number of cracks in the filling wall decreases, and the stability of the filling wall gradually improves; thus, by splitting the roof rock at the optimal location, the filling wall can be maintained in a stable state. Additionally, we conducted a sensitivity analysis that demonstrated that the higher the coal seam strength, the fewer cracks occur in both the filling wall and the coal wall, and the less failure they experience. With the main roof fracturing into a cantilever structure, the higher the immediate roof strength, the fewer cracks are in the filling wall. With the critical rock block fracturing above the roadway, an optimal strength of the immediate roof can be found that will stabilize the filling wall. This study presents a theoretical investigation into stabilization of the filling wall, demonstrating the significance of pre-splitting the roof rock at a desirable location. © 2015 Springer-Verlag Wien


Zhang N.-B.,China University of Mining and Technology | Zhang N.-B.,Key Laboratory of Deep Coal Resource Mining CUMT | Liu C.-Y.,China University of Mining and Technology | Liu C.-Y.,Key Laboratory of Deep Coal Resource Mining CUMT | And 4 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2015

In order to automatically identify the gangue mixed in the top-coal caving when it is drawn, the method of natural radiation was put forward. Then the flutuation of low level nature radiation radiated by gangue and the relationship between measure time and counting rate were analyzed theoretically to conform the radiate identification threshold and the accurate judgment threshold. In addition, several experiments were conducted to demonstrate all these thresholds, by which the real response characteristic was proved synchronously. All these were provided as a basis for identifying the gangue mixed in the top-coal caving by the natural radiation identification technology. ©, 2015, China Coal Society. All right reserved.


Yao Q.,China University of Mining and Technology | Yao Q.,Key Laboratory of Deep Coal Resource Mining CUMT | Li X.,China University of Mining and Technology | Li X.,Key Laboratory of Deep Coal Resource Mining CUMT | And 7 more authors.
Arabian Journal of Geosciences | Year: 2015

We carried out uniaxial compressive experiments on coal specimens with different moisture contents to gain a better understanding of the water-induced weakening characteristics of coal. The effects of moisture content on the strength and deformation characteristics of the specimens were analyzed. The results of the uniaxial compressive experiment demonstrate that the full stress–strain curve presents plastic deformation characteristics with the increase of the moisture content in the coal specimens. A positive linear relation between the peak strain and moisture content and a negative one between the compressive strength and moisture content were observed. The results also show that the elastic modulus and the moisture content satisfy a negative exponential function. Taking the obtained relation as boundary conditions and applying the statistical damage theory and strain equivalence hypothesis, we derived a statistical constitutive damage model for coal which can reflect the effects of the moisture content. © 2015, Saudi Society for Geosciences.


Liu S.,Key Laboratory of Deep Coal Resource Mining CUMT | Liu S.,China University of Mining and Technology | Sun B.,Key Laboratory of Deep Coal Resource Mining CUMT | Sun B.,China University of Mining and Technology | And 2 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2016

Element size (ES) affects the predictions of numerical simulations of rock mechanics. On this basis, we use the geotechnical modeling code FLAC3D with a strain-softening constitutive model to carry out uniaxial compression modeling of rock specimens having different ES to elucidate the effect of ES on specific failure mechanisms. The default simulation parameters, the loading velocity and model size are determined before conducting the parametric sensitivity simulations. It is found that the uniaxial compressive strength and peak strain of the specimen decreases in power function for bigger ES. Furthermore, shear failure percentage increases with increasing cohesion and friction angle, while tensile failure percentage shows the opposite trend; higher tensile strength can effectively restrict the initiation and percentage of tensile failure. Then, the effect of ES on failure mechanism of rock specimen is simulated and the results reveal that changing the value of any simulation parameter, the shear failure percentage increases and the tensile failure percentage decreases with increasing ES. This study serves as a guide to choosing the appropriate ES to resolve the failure mechanisms in numerical simulations of rock materials. © 2016 ejge.


Yao Q.,China University of Mining and Technology | Yao Q.,Key Laboratory of Deep Coal Resource Mining CUMT | Li X.,China University of Mining and Technology | Li X.,Key Laboratory of Deep Coal Resource Mining CUMT | And 6 more authors.
Shock and Vibration | Year: 2016

The 6163 haulage roadway in the Qidong coal mine passes through a fault zone, which causes severe deformation in the surrounding rock, requiring repeated roadway repairs. Based on geological features in the fault area, we analyze the factors affecting roadway deformation and failure and propose the concept of roadway sensitive to stress disturbance (RSSD). We investigate the deformation and failure mechanism of the surrounding rocks of RSSD using field monitoring, theoretical analysis, and numerical simulation. The deformation of the surrounding rocks involves dilatation of shallow rocks and separation of deep rocks. Horizontal and longitudinal fissures evolve to bed separation and fracture zones; alternatively, fissures can evolve into fracture zones with new fissures extending to deeper rock. The fault affects the stress field of the surrounding rock to 27 m radius. Its maximum impact is on the vertical stress of the rib rock mass and its minimum impact is on the vertical stress of the floor rock mass. Based on our results, we propose a zonal support system for a roadway passing through a fault. Engineering practice shows that the deformation of the surrounding rocks of the roadway can be effectively controlled to ensure normal and safe production in the mine. © 2016 Qiangling Yao et al.

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