两类岩石声发射事件与Kaiser效应点识别方法的试验研究

EXPERIMENTAL STUDY OF TWO TYPES OF ROCK SAMPLE ACOUSTIC EMISSION EVENTS AND KAISER EFFECT POINT RECOGNITION APPROACH

岩石声发射(AE)是研究岩石内部变形与破坏机制和测量地应力的重要手段之一,但利用AE Kaiser效应测量地应力尚未标准化,许多情况下Kaiser效应点不易判别。为了提高Kaiser效应点的识别能力,对取自鄂尔多斯盆地的21块砾岩、砂岩、泥岩等岩芯开展单轴压缩AE测试试验。分析不同应力下AE的规律以及岩性、加载模式和AE参数对Kaiser效应点识别的影响。结果发现:不同载荷条件下AE事件具有不同的数量、能量和频率特征,在Kaiser效应点判别方面,砾岩比砂岩和泥岩更易获得地应力读数;循环加载优于分级循环加载,优于单次加载模式;累积能量优于振铃数和AE数。结合岩芯不同应力下的微观变形破裂机制,可以认为,存在2种类型的AE事件:一为原有裂隙闭合和颗粒间摩擦引起的摩擦型AE,一为新裂隙扩张引起的破裂型AE,破裂型AE能够更好地反映AE对应力的记忆。为了突显Kaiser效应点,应尽量压制摩擦型AE,突出破裂型AE。建议在地应力测试中采用循环加载方式消除摩擦型AE的影响,预压应力水平应超过预先估计的地应力,采用累积能量作为Kaiser效应点的识别参数。

Acoustic emission（AE） is an important means to study rock internal micro-deformation and failure mechanism,the Kaiser effect is one of the common used methods of geostress measurement which is not standardized now.In many cases the Kaiser effect points are not obvious.In order to improve the ability of identifying Kaiser effect point,uniaxial compressive AE experiments of 21 rock samples are carried out.The samples derived from Ordos basin and consist of conglomerate,sandstone and mudstone.Comparison of the influence of lithology,loading mode and AE parameters on Kaiser effect point recognition are made.The results show that conglomerate is better than sandstone and mudstone;cyclic loading is better than step cyclic loading and monotonic loading;accumulated energy is better than AE and counts for identifying Kaiser effect point.The analysis of counts,power and frequency of AE events and the deformation and cracking micromechanism of rock samples under different load levels and cycles,suggesting that there are two types of AE events：one is frictional AE caused by the closure of original cracks and friction between the particles of rock;the other is cracking AE produced by the new failure extension or dislocation.Suppressing frictional AE and highlighting cracking AE can make Kaiser effect point more clear.It is recommended that the cyclic loading should be used to eliminate the frictional AE,and accumulated energy should be used to indentify Kaiser effect point,and the pre-loading stress level should exceed the estimated geostress.