Study on failure evolution of in-seam boreholes under cycle constant vertical loadings
WANG Zhiming1，SUN Yuning1，2，ZHANG Shuo1，SONG Weibin1，2，WANG Yonglong1，2
(1. School of Energy Science and Engineering，Henan Polytechnic University，Jiaozuo，Henan 454000，China；
2. State and Local Joint Engineering Laboratory for Gas Drainage and Ground Control of Deep Mines，Henan Polytechnic University，Jiaozuo，Henan 454002，China)
Abstract：To illuminate the long-time failure mechanisms for in-seam boreholes influenced by mining disturbances，the model experiment tests under a cyclic vertical stress were carried out by employing a independently-developed bi-direction loading device. Results show that the shrinkage of the borehole has obvious time effect at the constant stress stage and increases at the boost stress stage，which can be described well by the introduced borehole shrinkage model. Cycle loading makes the borehole shrink but the shrinkage rate decreases with increasing the cycle number. At the initial stage after drilling，the surrounding rock damages intensely with tiny fractures accompanied by no obvious cracks on the hole wall，which mainly causes borehole shrinkage. At the constant stress stage at the first cycle，the damage of the surrounding rock continues and tends to be stable，and the damage on the hole wall is enhanced. At the boost stress stage，the damage on the hole wall increases further and the damage range is enlarged，which raises the possibility of rock peeling from the hole wall. Meanwhile，the influence of stress boosting to the damage of the surrounding rock decreases with increasing the cycle number of loading. After repeatedly loading cycles，the damage of the surrounding rock accumulates and fractures propagate and link，inducing serious instability of the hole.
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2020, Vol. 39 
