Experimental study on influence of lithology on directional propagation law of type-I cracks

Abstract

To study the influence of lithology on the directional propagation law of rock type-I cracks, a simple crack directional propagation device was used to conduct loading tests on three rock types. The acoustic emission (AE) and displacement field characteristics during crack directional propagation were analyzed, and the propagation mechanism of type-I cracks was discussed. The results indicate that the post-peak load curve of white sandstone showed a gradually decreasing trend, while marble and grey sandstone showed a steep decreasing trend. The AE evolution during crack propagation can be divided into four stages: quiet, slowly increasing, booming, and decreasing. For white sandstone, the duration of the first three stages was short, and the decreasing stage was long. However, the opposite trend was observed for the other types. The crack propagation process includes three stages based on the evolution law of the horizontal displacement field: elastic deformation, microcrack nucleation and coalescence, and crack initiation and propagation. The white sandstone enters the microcrack nucleation and coalescence stage earlier than marble and grey sandstone. The length of the fracture process zone of white sandstone was larger than those of marble and grey sandstone; thus, its crack directional propagation rate and stability were lower.

摘要

为揭示岩性对岩石I型裂纹定向扩展的影响规律,采用一种简易裂纹定向扩展装置开展白砂岩、 灰砂岩和大理岩3 类典型岩石加载试验,研究不同类型岩石I 型裂纹定向扩展过程中变形场及声发射演 化特征,探讨岩性影响下I 型裂纹扩展机制。研究结果表明:白砂岩峰后荷载曲线呈**缓降低趋势, 而大理岩和灰砂岩峰后曲线则呈陡降趋势,且其断面**整度高于白砂岩的,脆性断裂特征更为显著; 根据水**位移场演化规律,可将岩石I 型裂纹扩展过程划分为弹性变形、微裂纹集结成核和裂纹起裂 扩展3 个阶段,而白砂岩进入微裂纹集结成核阶段则远早于大理岩和灰砂岩;岩石I 型裂纹扩展全过程 中声发射演化可划分为**静期、活跃期、突增期和回落期4 个阶段,其中白砂岩**静期、活跃期及突 增期持续时间短、回落期持续时间长,而大理岩和灰砂岩则与之相反;岩石I 型裂纹扩展的本质是断 裂过程区孕育过程,由于白砂岩断裂过程区长度大于大理岩和灰砂岩的,造成其裂纹定向扩展速度及 稳定程度均低于其他两类岩石。