加卸荷条件下灰岩能耗变化规律试验研究

Experimental study of energy evolution of limestone under loading and unloading conditions

对灰岩开展单轴、常规三轴与峰前卸荷试验,对比分析不同应力路径下灰岩变形过程的能量变化特征。试验分析表明,灰岩加荷破坏和卸荷破坏的能量变化规律存在明显差异。由于围压抑制了裂纹的扩展,与单轴压缩破坏相比,常规三轴压缩试验灰岩吸收的总能量U和积蓄的弹性能eU更多。常规三轴试验灰岩积蓄的弹性能eU在峰值强度前一直增加,而卸荷破坏的弹性能eU在卸荷开始后基本不变,说明卸荷破坏释放的弹性能eU主要是在加荷阶段累积完成的,岩体所处的初始地应力状态决定了其破坏的能量释放量。加荷和卸荷应力路径下,灰岩临近破坏点耗散能dU都快速增加,但是卸荷破坏耗散能dU增速远大于加荷破坏耗散能增速,耗散能的迅速增加表明岩石破坏的发生。随着围压升高,灰岩吸收的总能量U和储存的弹性能eU逐渐升高。随着卸荷速度增加,灰岩吸收的总能量U、储存的弹性能eU和耗散的应变能dU逐渐减小。

According to the results of limestone samples under uniaxial compression test, conventional triaxial test and unloading test, energy evolution characteristics of limestone during the whole-process deformation are analyzed. Results show that rock failure laws of energy evolution are different between loading and unloading. The confining pressure restrains the internal crack growth. The absorbed total energy Uand elastic energy Ue in conventional triaxial compression test are larger than that of uniaxial compression test. The elastic energy Ue continues increasing before peak strength. However, it remains the same during the unloading stage. The elastic energy U~ with release availability mainly accumulates in the loading process prior to the unloading process. The geostress state before engineering excavation determines the releasing amount of elastic energy. The dissipated energy Ud increases quickly near the peak strength. But the increasing velocity of dissipated energy under unloading stress path is faster than that under loading stress path. The rapid increase of dissipated energy indicates the occurrence of rock failure in loading and unloading stress paths. The absorbed total energy Uand elastic energy Ue increase with the confining pressure increasing. The absorbed total energy U, elastic energy Ue and dissipated energy Ud decrease with the unloading velocity increasing.