Abstract
Understanding the acoustic emission effects on bolts under cyclic loading is of great significance for the support of roadways. The presented research focuses on the acoustic emission characteristics of bolts under cyclic loading. The following main conclusions were drawn: (1) With a higher loading frequency, the acoustic emission counts rate increases, while the total energy released in a given cyclic loading path decreases. (2) A fitting formula is established according to the relationship between the tension amplitude and cumulative acoustic emission counts, which can analyze the tension magnitude level of the cyclic load. (3) A damage factor for a cyclic load is proposed based on the acoustic emission counts generated during the cyclic and monotonic loading process that can analyze the degree of damage to the anchorage system caused by the cyclic load. (4) Based on the spatial distribution of the acoustic emission orientation points and the acoustic emission energy generated during the pull-out process, the acoustic emission damage evolution process of the anchorage specimens is deduced, and the mechanism of the high stability of the pretension anchorage system after cyclic loading is analyzed. The above conclusions may provide some experimental references for the application of acoustic emission technology in bolts supporting roadways.
Highlights
The pretensioned bolt has become the main support technology in underground coal mining
Pretensioned bolt support plays an important role in the stability of roadways in underground coal mines
The mechanical response of bolts under cyclic loading will affect the stability of the roadways
Summary
The pretensioned bolt has become the main support technology in underground coal mining. From the pull-out test of pretensioned anchored specimens, the cumulative AE counts curves of 12 specimens show a logarithmic model under cyclic loading at different levels. I, II, III, IV, and V refer to the tensile levels of the cyclic load; the curve fitting formulas and correlation coefficients are indicated by arrows In this formula, A and B are the influencing factors of the cyclic tension amplitude, t is the time, and y is the cumulative AE counts f = 1=T ð2Þ. An appropriate pretension condition can effectively improve the reliability of an anchorage system under cyclic and monotonic action
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