ABSTRACT:

This paper discusses the forewarning features associated with failure of coal-rock composite samples under uniaxial compression. The characteristics of energy dissipation and transfer in the failure process are analyzed. An experimental system is set up to investigate the failure mechanism and forewarning messages of the of coal-rock composite specimens. In order to investigate the thermal infrared (TIR) and acoustic responses of different composite samples, tests are performed on samples consisting of "Sandstone-Coal-Mudstone" cylinders and "Sandstone-Coal" cylinders, respectively. Uniaxial compressive tests are carried out to observe the features of TIR, acoustic emission and strain forewarning messages during the failure process. Statistical analyses on the forewarning stresses are conducted based on infrared radiation temperature, infrared radiation images, acoustic emission and strain datum. The analytical results show that the coal-rock composite specimens are in the stress accelerated accumulation state before failure. Moreover, forecasting failure of composite samples is rather difficult than that for normal coal specimens.

1 INTRODUCTION

Previous studies show that instability hazards and failure of geological rock masses, for instance, earthquake, coal bump and rockburst, is the interaction results of instable deformation of mechanical systems formed by some geological bodies. Coal mine dynamic disaster is essentially the occurrence of overall instability of "coal-rock" system subjected to mining disturbances. To be more accurate, instability of either coal or the surrounding rock in the system leads to failure of the coal-rock system. Most researchers consider that coal dynamic failure is the manifestation of instability of coal-rock system; coal stratum should be taken as coal-roof system and full consideration should be given to the interaction between sub-systems, namely, roof, coal stratum and floor; the effects of sub-systems and composite system to dynamic failure shall be studied from the point of view of accumulation and release of deformation energy.

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