应力条件对受载煤体声发射活动特征的影响研究

Study on effect of stress condition on acoustic emission activity feature of loaded coal in failure process

为研究外部应力条件对受载煤体的声发射活动特征的影响作用,采用岩石力学试验系统和声发射仪,开展了单轴、不同围压三轴、卸围压三类应力条件下的煤样破坏试验,对比分析了煤体在不同应力条件下的破坏特征及声发射活动特征。试验结果表明:煤体的声发射活动宏观上与煤体的破坏阶段相对应,应力条件对煤的破坏特征及声发射活动特征具有重要影响作用。在增围压作用下,煤体的弹性模量、强度增加,主破裂面与轴向加载方向的角度逐渐增大,主破裂机制由张拉破坏向剪切破坏转变;在卸围压作用下,煤的主破裂机制由剪切破坏向张拉破坏转变。在围压应力增加条件下,在弹性变形阶段,煤体的声发射事件显著减少;在屈服变形阶段,声发射事件的能量逐步降低,并且能量的分布形态从相对"聚集"向相对"分散"的转变;在峰后变形阶段,煤体呈现渐进损伤的延性破坏特征,声发射活动持续逐步降低。在三轴卸载围压应力条件下,在煤体屈服阶段,声发射事件率与能量都随着应力的快速跌落而迅速增加,声发射活动趋于活跃,煤体的破坏方式最为剧烈。

In order to study the effect of external stress condition on AE activity of loaded coal in the failure process,coal failure experiments under 3 kinds of stress condition,uniaxial,conventional triaxial,and unloading confining stress,are carried out with rock mechanics testing machine and AE monitoring instrument,the corresponding failure and AE activity characteristics of coal are compared and analyzed.The results show that AE activity of coal,in macro perspective,is related to phases of coal failure process,and the stress condition has an important influence on the failure characteristic and AE activity of coal.Under the effect of confining stress increasing,elastic modulus and strength increase,the main fracture angle to axial main stress direction is increasing,and main failure mechanism changes gradually from brittle tensile to shear failure,and the contrary mechanism change when confining stress unloading.In condition of confining stress increasing,AE event reduces in phase of elastic deformation;in phase of yield deformation,the general energy level of AE event is decreasing,and the energy distribution of AE events is transforming from relative disperse condition to relative concentration condition with the increasing of confining stress;and in phase of post-peak,the damage of coal shows progressive failure characteristics and the AE activity keeps gradually decreasing.In condition of confining stress unloading,and the AE event rate and energy increase rapidly with rapid drop of axial stress,the failure mode of coal is the most drastic in all stress conditions.