Development of Torque Logging System for Predicting Rockburst and Coal Outburst

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A torque logging system for recording the torque during the test boring or the advance boring has been developed to facilitate an alternative of predicting measures for rockburst or coal outburst. The system is intrinsically safe for use in underground coal mine, and it is available for both the dry boring and the wet boring. The torque detected by a transducer is transmitted via a radio wave and recorded on the taperecorder which is housed in a flame-proof box. The tests have proved that the system is capable of torque data acquisition during underground boring without any sorts of trouble.In addition to developing a new system for torque logging, a laboratory experiment has been carried out to comprehend the relation between the torque during boring, the volume of drillings, the mechanical properties of coal and the stress state in coal seam. The boring simulation has demonstrated that both the torque and the volume of drillings increase with increasing of the mean stress applied to the coal specimen, and resulted in jamming when the mean stress was over three times as large as the uniaxial strength of the coal.The relation between the torque during boring and the remote stress around the borehole has also been confirmed by the theoretical analysis in which the coal seam was represented by means of a linearly elastic and strain-softening material. This mechanical model enables us to predict the radius of elastic-plastic boundary around the borehole as well as the radial displacement at the inner surface of the borehole.