矿物颗粒大小组成与岩石声发射相对平静期关系的研究

The technology of acoustic emission (AE) is widely applied in rock engineering. The theory about rock AE is lag behind the engineering application due to the complexity of rock. A great deal experimental results have shown that there exists a relatively tranquil period phenomenon of AE before rock failure. There are no generally accepted achievements for the condition and the cause about tranquil period of AE till now. This may be one of the important reasons why such rock AE filed as prediction of rock failure, in-situ stress measurement by Kaiser effect still rested on the stage of qualitative. AE experiments of rock and simulation materials with different mineral granular sizes will be conducted. Based on the experiment results numerical simulation by the aid of PFC and theoretical analysis will be also carried out for further study. The internal relationship between the duration time of tranquil period and the distribution of mineral granular sizes and the homogeneous degree will be revealed. The corresponding stress at the start and stop time of tranquil period with the crack initiation stress and the crack damage stress will be comparatively analyzed. Characteristics of AE nucleation and distribution of the sound source position before and after the tranquil period will be studied based on the test of AE location. Moreover, the relationship between mineral granular sizes with the tranquil period will be studied by using PFC. Based on the above achievements the mechanism of tranquil period phenomenon of AE and its reasons concern with the granular size will be revealed. The research results have an important theoretical value for understanding Kaiser effect and prediction of rock failure.

声发射技术在岩石工程等领域有着广泛应用，但由于岩石材料的复杂性导致岩石声发射在理论方面的研究滞后于工程应用。大量试验表明，岩石破坏前存在声发射相对平静期，出现平静期的条件、原因等还没有公认的研究结论，这也是目前岩石破裂声发射预测、凯泽效应测量地应力等仍停留在定性阶段的重要原因之一。本项目拟进行不同矿物颗粒大小组成的模拟材料、岩石材料声发射试验、PFC数值模拟和理论研究。通过试验得到不同颗粒大小组成条件下，平静期历时与均质度的关系，平静期起止点对应应力与起裂应力、损伤应力的关系；通过声发射定位试验，寻求不同颗粒大小组成条件下，平静期前后声源分布、成核特征；通过PFC数值模拟进一步分析平静期与材料内部颗粒大小组成的关系，在上述研究基础上，探明岩石声发射平静期与矿物颗粒大小组成的关系，为揭示岩石声发射凯泽效应机理、岩石破裂声发射预测等提供重要科学依据。

声发射技术在岩石工程等领域有着广泛应用，但由于岩石材料的复杂性导致其声发射在理论方面的研究滞后于工程应用。本项目以岩石破坏前存在的声发射相对平静期为切入点，提出了利用类岩石材料研究矿物颗粒大小与声发射相对平静期之间的关系，通过不同粒径类岩石材料声发射试验，试验结果表明：粒径越大，声发射活跃期越靠后，粒径在0.08-2mm之间时，粒径越大类岩石材料声发射相对平静期现象越普遍；粒径在1-2mm范围内，粒径越大相对平静期历时越长。声发射相对平静期处低主频波动范围变窄且无较低主频出现，相对平静期后试件完全破坏或应力出现明显下降时，较低主频信号才会产生。110-120kHz为类岩石材料破裂过程的敏感频段，该频段出现率在峰值破坏前兆相对平静期处明显降低。采用PFC数值模拟对岩石声发射相对平静期与其局部强度异常区之间的关系进行了研究，结果表明：随着强度异常区面积占比上升，裂纹从集中分布转为弥散分布，声发射平静期历时减短；强度异常区域面积越小，越容易产生较大的声发射事件，声发射平静期现象越显著。异常区相同面积条件下，贯通与非贯通、长宽比的变化，相应的声发射平静期表现不同，因此，岩样刚度异常区域的空间分布对声发射平静期具有一定影响。红砂岩声发射平静期试验结果表明，声发射相对平静期出现在峰值应力90%左右，相对平静期对应的应力增加缓慢而应变增加较快，出现明显的“耗时”现象；存在相对平静期的试件，由相对平静期起始点应力分别与裂纹闭合应力、起裂强度及损伤强度的拟合公式可推断平静期起始点应力，可将相对平静期起始点应力作为岩石破坏的预警值。研究成果为声发射技术在岩石工程临界破坏失稳监测、预测领域的应用提供了必要的科学依据。