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Hong Y.,China University of Mining and Technology | Fulian H.,China University of Mining and Technology | Fulian H.,State Key Laboratory of Coal Resources and Safe Mining
International Journal of Mining Science and Technology | Year: 2012

The support of coal roadways is seriously affected by intense dynamic pressures. This can lead to problems with large deformation of the roof and the two side walls of coal roadways. Rapid convergence of the walls and roof, a high damage rate to the bolts and cables, or even abrupt roof collapse or rib spalling can occur during the service period of these coal roadways. Analyzing the main support measures used in China leads to a proposed new cable truss supporting system. Thorough study of the entire structure shows the superiority of this design for roadways suffering under dynamic pressure. A corresponding mechanical model of the rock surrounding the cable truss system is described in this paper and formulas for calculating pre-tightening forces of the truss cable, and the minimum anchoring forces, were deduced. The new support system was applied to a typical roadway affected by intensive dynamic pressure that is located in the Xinyuan Coal Mine. The results show that the largest subsidence of the roof was 97 mm, the convergence of the two sides was less than 248 mm, and the average depth of the loose, fractured layer was only 6.12 mm. This proves that the new support system is feasible and effective. © 2012 Published by Elsevier B.V. on behalf of China University of Mining & Technology. Source


Lu J.-G.,State Key Laboratory of Coal Resources and Safe Mining | Lu J.-G.,China University of Mining and Technology | Pan L.,China University of Mining and Technology
Meitan Xuebao/Journal of the China Coal Society | Year: 2010

Based on the statistical analysis of law of microseismic events releasing energy, researched the tendency of transformations of microseismic energy with the elapse of time, and deem that the high energy events are the necessary condition of coal burst. Taking Xinzhouyao Coal Mine of Datong City as an example, respectively applying the seasonal ARIMA model and threshold autoregressive model of time series models to forecast the microseismic events releasing energy in the future, and compared with the advantages and disadvantages of two methods and applicable conditions. The characteristic function of the variance change of the microseismic energy was constructed, and based on it, put forward a new recognition method for the risk model of coal burst. Research shows that ARIMA seasonal model can effectively predict the futural microseismic releasing energy in cyclical obvious high-energy microseismic events. However, the threshold autoregressive model is suitable to predict high microseismic energy releasing process of non-significant cyclical trend. The criterion of the characteristic function of microseismic energy variance can effectively predict coal burst. Source


Wang E.,State Key Laboratory of Coal Resources and Safe Mining | Wang E.,China University of Mining and Technology | Jia H.,China University of Mining and Technology | Song D.,China University of Mining and Technology | And 3 more authors.
International Journal of Rock Mechanics and Mining Sciences | Year: 2014

Using an established acoustoelectric signal testing system, we conducted a series of experiments on coal rock samples of lower strength under uniaxial compression and shear loading to study the characteristics of ultralow frequency (ULF) electromagnetic radiation (EMR) signals emitted during their damage and failure, compared them with signals of very low frequency (VLF) (5. kHz), middle frequency (MF) (300. kHz) and acoustic emission (AE) (42.3. kHz), and explored the generation mechanism of this ULF EMR. Using our self-developed ULF signal acquisition instruments, we monitored the ULF EMR signals at the mining face, and studied the space and time distribution laws of ULF EMR in the front of the mining face. The results showed that the coal rock materials subject to uniaxial compression and shear loading can produce ULF EMR signals, which are well correlated with stress, and AE signals. The ULF signals emitted from the two processes are caused firstly by the changes in the induction field due to charges moving and secondly by the piezomagnetic effect resulting from some metal minerals in the coal rock materials after applying stress. Under rock pressure in mines, the coal mass ahead of the face during its deformation and failure emits strong ULF EMR with a strong ability to resist interference. The time and space distributions of these EMR are well correlated with stress in coal mass in the front of the mining face. © 2014 Elsevier Ltd. Source


Hongwei W.,China University of Mining and Technology | Yaodong J.,China University of Mining and Technology | Yaodong J.,State Key Laboratory of Coal Resources and Safe Mining | Jie Z.,China University of Mining and Technology | And 2 more authors.
International Journal of Mining Science and Technology | Year: 2013

This study presents a numerical investigation to assess the risk of coal bumps and produces a stress-relief technology using boreholes to mitigate risk during the extraction of an island longwall panel. Based on the geological condition in an island longwall panel in the Tangshan Coal Mine, Tangshan, China, a numerical FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) model was established to determine and to map the zones in the panel with a high risk for coal bumps. The results of the numerical modeling show that the roof deformation starts to occur at more than 30 m ahead of the longwall face and the deformation starts to accelerate after a distance of 10 m in front of the longwall face. Large and rapid roof deformation is considered to be an important precursor of coal bump occurrence during the extraction of an island longwall panel. Based on the numerical results, a stress-relief technology using boreholes, which was employed to release abutment pressure, was investigated through numerical methods. The modeled results suggest that the peak stress concentration could be released by drilling boreholes in the zones prone to coal bumps. The effectiveness of the stress release increased with the borehole length and decreased with the borehole spacing. © 2013 Published by Elsevier B.V. on behalf of China University of Mining & Technology. Source


Ju J.,China University of Mining and Technology | Ju J.,State Key Laboratory of Coal Resources and Safe Mining | Xu J.,China University of Mining and Technology | Xu J.,State Key Laboratory of Coal Resources and Safe Mining
International Journal of Rock Mechanics and Mining Sciences | Year: 2013

Strata behaviour during the operation of super great mining height (SGMH) longwall face is different from that of normal mining height due to the extra large boundary of caved roof strata. The key to control the strata behaviour is to understand the structural characteristics of key strata (KS) and its movement law. Through field observation, physical model simulation and theoretical analysis on the first longwall face with 7.0. m mining height in the world, three kinds of structural model, which are affected by the relative position of KS in the overburden, are found and defined. Model A is defined as when the stable voussoir beam structure can be developed in the overlying KS and the strata behaviour is gentle. Model B is defined as when the cantilever structure is developed in the first KS while voussoir beam structure is developed in other overlying KS, and the continuous distance of periodic weighting (CDPW) is typically longer compared with that of normal mining height face. As to Model C, the structure of KS is the same as that in Model B, but the first KS will be forced to break in advance due to the break of the second adjacent overlying KS, which will present the weighting step and strata behaviour severity with a periodic alternating between long/gentle and short/strong. With respect to the three kinds of structural models, a method which is suitable for the calculation of working resistance for 7.0. m height chocks was proposed. The suitable working resistance for the 7.0. m height chocks of LW22303 face in Bulianta coal mine was determined to be 17,612. kN. © 2012 Elsevier Ltd. Source

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