摘要
为精准获得岩石Ⅰ型裂纹扩展演化全过程,采用一种简易裂纹定向扩展装置开展了不同岩性试样裂纹扩展试验研究,借助声发射及数字散斑技术对裂纹扩展全过程进行了监测,建立了裂纹定向扩展力学模型,分析了裂纹扩展过程中声发射及变形场的演化规律,提出了评价岩石Ⅰ型裂纹扩展难易程度的能量指标C_(E),探讨了Ⅰ型裂纹定向起裂扩展机制。结果表明:该简易裂纹定向扩展装置能够有效实现Ⅰ型裂纹沿预定方向稳定扩展,其起裂角均小于10°,同时通过简化力学模型计算得到白砂岩、灰砂岩的裂纹扩展峰值强度与巴西劈裂抗拉强度相比偏差分别为22.76%、7.53%;根据变形场演化规律,可将裂纹扩展分为微裂隙发育(散斑变形场分区不明显)、主控裂纹孕育(散斑变形场出现分区现象)和主控裂纹扩展3个阶段;声发射演化过程可分为平静期、缓增期、急增期和降低期4个阶段,由于灰砂岩相较于白砂岩质地更致密、更坚硬,导致其声发射平静期长,而后3个阶段持续时间短;将载荷-位移曲线峰前与峰后的面积之比定义为评价岩石Ⅰ型裂纹扩展难易程度的能量指标C_(E),计算得到灰砂岩、白砂岩的C_(E)分别为13~16、1~2,表明C_(E)可有效评价岩石Ⅰ型裂纹扩展难易程度;岩石Ⅰ型裂纹起裂扩展机制可概况为:在加载峰值前裂隙尖端受最大拉应力作用,存储的弹性能快速增加、耗散能缓慢增加,但在加载峰值后裂隙尖端存储弹性能超过其储能极限迅速释放,此时输入能大部分转化为耗散能促进主控裂纹快速扩展。后续将对裂纹定向扩展试验装置进一步优化改进,以期为裂纹扩展机制、岩石破坏前兆信息、裂纹止裂原理等研究提供一种新方法,同时为工程现场煤岩层定向爆破、压裂、止裂等相关技术优化提供理论指导。
To obtain the rock type-Ⅰ crack propagation process accurately, a simple crack directional propagation device was used to test the crack propagation of different rock types. The crack propagation process of rock is monitored with acoustic emission(AE)and digital image correlation method(DICM). A mechanical model of crack directional propagation was established. Then, AE and deformation field evolution laws during crack propagation process are analyzed, and a new crack propagation energy index(C_(E)) is proposed to evaluate the difficulty of rock type-Ⅰ crack propagation and the crack initiation and propagation mechanism is discussed.The results show that, the simple crack directional propagation device can effectively realize the stable propagation of type-Ⅰ crack along the predetermined direction, the crack initiation angle is less than 10°, and the deviations between the peak strength of crack propagation calculated by simplified mechanical model and the tensile strength of Brazilian splitting are 22.76% and 7.53% for white sandstone and grey sandstone, respectively. According to the deformation field evolution law, the crack propagation can be divided into three stages: microcrack development(speckle deformation field is still uniform), main crack propagation(zone phenomenon appears in speckle deformation field) and main crack propagation. Four stages including quiet stage, slow increase stage, rapid increase stage and decreasing stage can be identified in the AE evolution process. Compared with white sandstone, the gray sandstone is denser and the main cracks are fully developed, resulting in a long quiet stage of AE, while the last three stages are short. The area ratio of pre-peak area to post-peak areaof load-displacement curve was defined as C_(E), the C_(E) of gray sandstone and white sandstone are 13-16, 1-2, respectively, which shows that the C_(E) can effectively evaluate the difficulty of type-Ⅰ crack propagation. Rock type-Ⅰ crack initiation and propagation mechanism can be summarized as follows: before the peak, the prefabricated crack tip is subjected to the maximum tensile stress, the elastic energy increases rapidly, and the dissipated energy increases slowly;nevertheless after the peak, elastic energy exceeds its energy storage limit and is released rapidly, most of the input energy is converted into dissipated energy, which results in a propagation rapid of crack. In the future, the crack directional propagation device will be optimized and improved, and it is expected to provide a new method for the study of crack propagation mechanism, rock fail precursor information and crack arrest principle, and to provide theoretical guidance for the optimization of coal strata directional blasting, fracturing,fracture arrest and other related technologies in the engineering site.
作者
张东晓
郭伟耀
赵同彬
谷雪斌
陈玏昕
ZHANG Dong-xiao;GUO Wei-yao;ZHAO Tong-bin;GU Xue-bin;CHEN Le-xin(College of Energy and Mining Engineering,Shandong University of Science and Technology,Qingdao,Shandong 266590,China;State Key Laboratory Breeding Base for Mining Disaster Prevention and Control,Shandong University of Science and Technology,Qingdao,Shandong 266590,China)
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2022年第S02期231-244,共14页
Rock and Soil Mechanics
基金
山东省自然科学基金重大基础研究资助项目(No.ZR2019ZD13)
国家自然科学基金青年基金(No.51904165)
山东省自然科学基金(No.ZR2019QEE026)。
