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Abstract The strain gauge instrumented bolts have been installed on the roof strata of a longwall roadway to evaluate the performance of a fully encapsulated bolt，in terms of the axial load，its distribution along the length of the bolt，and the bending moment of the bolt in different mining activities. The results indicate that during the heading development，the performance of roof bolts is dominated by the stress redistribution. After the stress settles，the load of the bolt varies with the time-dependent characteristics of the surrounding rock mass. During the longwall extraction，the load on the bolts increases with the face approaching；and degradation of bolt load can be detected，when the face is close to the bolt；it indicates that the bolt is no longer able to provide its full function – to prevent the deformation of roof strata，due to failure of grouting material. It is found that the maximum axial load and bending moment on the bolt are increased 36% and 54% before and after extraction respectively；it is clearly indicated the different effects of static and dynamic loading conditions. It is also noted that the maximum bending moment is mainly located in the interface of different roof layers，which intends to move horizontally. The fully encapsulated bolt demonstrates two basic functions for reinforcing layered roof；firstly，preventing vertical movement of roof layers in different horizons；and secondly，providing shear resistance to prevent lateral movement between the roof layers.
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Received: 20 April 2009
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