单轴压缩下两种脆性岩石强度及声发射特性的试验研究

CHARACTERISTICS OF STRENGTH AND ACOUSTIC EMISSION OF GRANITE AND MARBLE UNDER UNIAXIAL COMPRESSION

脆性对岩石破裂机制及声发射特性具有重要影响。采用花岗岩及大理岩两种不同岩性的岩石,开展了单轴压缩及声发射测试试验,获取了两种岩石的强度及变形特性,并对其脆性大小进行定量评价,分析了单轴压缩过程中两种岩石声发射能量演化特性,结合声发射b值计算结果及其物理意义,对比了两种岩石破裂机制的差异性。结果表明:(1)试验所采用的两种岩石,花岗岩的σcd/σp之比介于0.676~0.745之间,平均为0.706,而大理岩的σcd/σp之比介于0.439~0.615,平均为0.52;(2)基于脆性评价指标,结合试样宏观破坏现象及形态,本次试验采用的花岗岩其脆性大于大理岩;(3)岩石脆性程度越大,在裂纹不稳定扩展阶段,在产生相同的轴向压缩变形的情况下,环向变形量越大;(4)强脆性的花岗岩在裂纹不稳定扩展阶段持续出现高能级的声发射信号,而弱脆性的大理岩则表现出能量持续降低的变化趋势,峰值强度后,弱脆性的大理岩其高能级能量的声发射信号更活跃;(5)单轴压缩下,与大理岩相比,花岗岩破坏过程中大尺度的破裂事件所占比例较大。

Brittleness has an important influence on rock failure mechanism and acoustic emission characteristics.Uniaxial compression and acoustic emission tests were carried out using two different lithological rocks of granite and marble.The strength and deformation characteristics of the two rocks were obtained,and the brittleness was quantitatively evaluated.The evolution characteristics of acoustic emission(AE)energy of two rocks during uniaxial compression were analyzed.Combined with the calculation results of AE b value and their physical meanings,the differences of two rock failure mechanisms were compared.The results are summarized as follows.(1)The ratio ofσcd/σp of the granite used in the experiment is between 0.676~0.745,with an average of 0.706,while that of the marble is in the range of 0.439 to 0.615,with an average value of 0.52.(2)Based on the brittleness evaluation index,combined with the macroscopic failure phenomenon and morphology of the sample,the granite used in this test is more brittle than the marble.(3)In the case of the same axial compression deformation generated during the crack unstable propagation stage,the greater the brittleness of the rock,the larger the amount of circumferential deformation.(4)The high-brittle granite exhibits sustained high-level acoustic emission signals during the crack unstable propagation stage,whereas the weak brittle marble shows a continuously decreasing trend.After the peak strength,the AE signal with high-value energy is more active for the weak brittle marble.(5)The ratio of macro-crack to micro-crack is larger for granite than that of marble during the destruction process under uniaxial compression.