Abstract: Using the coarse-grained granite from Dali, Yunnan, as the test material, a sample of 200mm?200mm?15mm in size was prepared. On the sample, V-shaped block boundaries consisting of en echelon faults (slots or prefabricated cracks) were cut, and the slots were filled with gypsum. According to the structural characteristics, the sample was divided into a few zones: zone A where faults converge, zone B where faults form left-lateral and left-stepping rock bridges, and zone C where faults form right-lateral and left-stepping rock bridges. Observational study was made by means of biaxial loading. The result of microcrack location shows that acoustic emission (AE) has the features of grouped occurrence in a region and grouped migration. Microcracks migrated from zone A to zone B and finally to zone C. In the initial stage of migration, AE events appeared alternatively in the place of original occurrence and the place where they migrate. In each stage, relatively large AE events occurred in each zone, but they concentrated relatively in zone C where they finally occur, and the sample ruptured finally when rock bridges in zone C broke down. The result of fixed strain showed 3 times sudden change, sudden rise or sudden fall, in accordance with the movement characteristics of AE of the zones A, B, and C. Analysis of the local b-value by the "accumulated frequency-energy level" relation showed that the b-value of the zone C reduced obviously before the main fracture. When examining from the structural characteristics, it can be seen that the three zones are the places where different structures meet each other and therefore are sensitive sections for events to occur. This has led to different orders of fracture or different precursor phenomena.

Key words: V-shaped structure, block, acoustic emission, AE intensity, b value

摘要： 试样采用200mm×200mm×15mm云南大理产粗粒花岗岩,其上切割出雁列式断层组成的V形块体边界,切缝以石膏填充。按构造特征,把样品分为几个区,其中A区为断层交汇区;B区为左行左列岩桥区;C区为右行左列岩桥区。采用双轴加压。文中详细讨论了岩样受压破坏过程中的声发射特征。微破裂定位表明,声发射有区域群发性和成群的迁移性。微破裂从A区向B区迁移最后到C区。在迁移初期,声发射在原发生地与迁移地两处交替发生。相对较大的声发射,每个时期每个区域均有发生,但C区即最后发生地相对集中,该处岩桥区断裂后试样崩溃。定点应变结果也出现了3次突跳,与声发射A,B,C区的声发射移动特征相吻合。用“累计频度-能级”关系对局部b值的分析显示:主破裂前,C区b值明显减小。从构造特征上看,三区为不同构造的相交处,为事件发生敏感地段,这就导致了不同的破裂顺序,甚至产生不同的破裂前兆现象。

关键词: V形构造, 块体, 声发射, AE强度, b值