易弹射煤体力学特性及能量演化机制

Mechanical properties and energy evolution mechanism of coal prone to ejection

通过开展不同主应力条件下真三轴加卸载试验,研究不同加卸载路径下易弹射煤体的力学特性、破坏特征及能量演化规律,揭示开挖卸荷易弹射巷道围岩弹射机制。研究表明:易弹射煤样在高应力单面卸荷比加载破坏更剧烈,当轴压为峰值的90%时卸荷,易弹射煤样表面出现一条大剪切裂缝,轴向应变率高,其自身破坏程度大,弹射现象明显;当轴压为峰值的80%,70%时卸荷,煤样未发生整体宏观破坏,轴向应变率低,自身的破坏程度小,仅在临空面产生张拉裂纹,弹射现象不明显;随着第二主应力的增大,在一定范围内对易弹射煤样有补强的作用,易弹射煤样内部复合型裂纹先增加后减小,破坏形态由剪切破坏转变为张拉–剪切复合破坏,最后发展为劈裂破坏,弹射剧烈程度呈现出先增加后减小的现象;高应力卸荷破坏过程中,弹性能转化为耗散能瞬间释放,耗散能占比急剧增大,抛离母体的碎块携带能量弹射出去,临空面出现明显的交叉网格裂缝,弹射现象明显;高应力易弹射煤样卸荷后张拉–剪切裂纹迅速扩展贯通,发生张拉–剪切复合破坏,弹射现象显著;卸荷后,易弹射煤样出现张拉–剪切裂纹,RA急剧值增高,AF值持续降低,AE呈现高能、高计、高幅、高频特征。研究结果可为类似地下工程开挖围卸荷岩微冲击现象控制提供借鉴。

In this paper,true triaxial loading and unloading tests under different principal stress conditions were conducted to study the mechanical properties,failure characteristics,and energy evolution laws of coal bodies that are prone to ejection under different loading and unloading paths,aiming to reveal the ejection mechanism of the surrounding rock of roadway that is prone to ejection after excavation and unloading.The results are as follows.Firstly,the damage of coal samples that are prone to ejection was more severe under high stress single-sided unloading than under loading;when the axial pressure is 90%of the peak value,a large shear crack appeared on the surface of the coal samples,the axial strain rate is high,its own damage degree is large,and the ejection phenomenon was obvious;when the axial pressure was 80%and 70%of the peak value,respectively,the coal samples did not undergo overall macroscopic damage,the axial strain rate is low,and the degree of damage is small,only generated tensile cracks on the free face,and the ejection phenomenon was not obvious.Secondly,the increase of the second principal stress had a reinforcing effect on coal samples that are prone to ejection within a certain range,the internal composite cracks of coal samples that are prone to ejection first increase and then decreased,and the failure mode changed from shear failure to tension-shear composite failure,and finally developed into splitting failure;the intensity of ejection first increased and then decreased.Thirdly,in the process of high stress unloading failure,elastic energy was converted into dissipated energy and released instantly,and the proportion of elastic energy increased sharply,causing the fragments being ejected from the mother body with energy;there were obvious cross mesh cracks in the free face,and the ejection phenomenon was obvious.Fourthly,for coal samples that are prone to ejection under high stress after unloading,the tension-shear cracks rapidly expanded and connected,resulting in tension-shear composite failure,and the ejection phenomenon was obvious;Fifth,tension-shear cracks appear in ejectable coal samples of after unloading,RA increased sharply and AF decreased continuously,AE showing the characteristics of high energy,high meter,high amplitude and high frequency.The study results can provide reference for the on trol of micro impact phenomena in unloading surrounding rock during excavation of similar underground engineering.