基于NMR和声发射的砂岩疲劳损伤试验研究

Experimental Study on Fatigue Damage of Sandstone Based on NMR and Acoustic Emission

为科学地评价工程岩体的长期稳定性和安全性,在实验室条件下对饱水砂岩开展循环加卸载试验,结合声发射技术与核磁共振分析技术两种手段探究其宏细观变形及疲劳损伤演化规律.研究结果表明:在循环荷载作用下,砂岩的声发射能量分布规律与轴向累积残余变形发展规律、应力-应变曲线滞回环变化规律一致,均能反映岩石在重复应力的作用下逐渐劣化至发生破坏;岩石疲劳损伤过程中的声发射能量幂律特征具有时间序列上的尺度不变性,循环中期幂指数可有效表征全过程能量分布;根据T2谱结果,定义系数K2为细碎裂隙与较大裂隙体积之比,循环过程中K2一直处于增加的状态,当K2值急剧下降时,砂岩有破坏的前兆;试件的AE特征与NMR特征均能体现岩石内部孔裂隙变化,其结果具有一致性,反映出岩石破坏是局部变形累积引起的整体疲劳损伤.

In order to evaluate the long-term stability and safety of engineering rock mass scientifically,cyclic loading and unloading test was carried out on saturated sandstone.Acoustic emission technology and nuclear magnetic resonance analysis technology were used to explore the macroscopic and microscopic deformation and fatigue damage evolution law.The conclusions are as follows:under cyclic loading,the distribution law of sandstone’s acoustic emission energy was consistent with the development law of axial cumulative residual deformation and the variation law of the stress-strain curve hysteresis loop.They all reflected the rock’gradual deterioration to damage under repeated stress.During rock fatigue damage,the power law characteristics of acoustic emission energy had scale invariance in time series,and the medium-term power index could effectively represent the energy distribution of the whole process.According to the result of T2 spectrum,the ratio of the fine fracture to the larger fracture volume was defined as K2.During the cycle,K2 was always increasing.When K2 dropped sharply,the sandstone showed symptoms of destruction;the AE and NMR characteristics of the specimen could reflect the cracks in the internal pores of the rock,and the results are consistent,which indicates rock damage is the overall fatigue damage caused by local deformation accumulation.