Propagation of Frictional Fractures under Complex Loading

岩石力学中最重要的挑战之一是开发工具和技术，以提供有关损伤的准确信息，即由于改变现有条件的活动而在岩体内部产生的新裂缝。普渡大学最近进行的实验室实验表明，通过监测在岩石中传播的纵波和横波的振幅变化，可以探测到岩石内部新裂缝的形成。实验还发现了失败前兆的存在。这些前兆的形式是透射波的振幅急剧下降，这种下降发生在应力水平远低于发生破坏/破坏的应力水平。这些发现有可能提供一种方法来预测即将发生的破坏，检测新的裂缝，并提供有关新裂缝的工程特性的信息，如刚度和可能的抗剪强度。该项目的重点是对这种潜力进行实验验证。将对受双轴和循环压缩载荷作用的预裂各向异性岩石进行一系列综合实验，以确定：(1)岩石中的裂缝起裂和聚并过程；(2)这些过程的地球物理特征，特别是破坏前兆的存在；(3)复杂荷载作用下岩石力学与地球物理响应的耦合。实验将在花岗岩、Austin Chalk Cordova cr<e:1>（一种显示地震各向异性的软岩）和砂岩上进行。这项工作是多学科的，因为它结合了两位主要研究人员在脆性材料压裂和应用于破碎岩石的地球物理方法方面的专业知识。这项研究对科学和社会的潜在影响是非常高的。首先，这项工作将有助于提高我们仔细检查岩石内部是否存在裂缝的能力，并推断裂缝的工程性质。这是一个重要的问题，限制了岩石力学、刚性土壤和其他材料领域的进步，因为在观察复杂载荷下岩土材料内部的开裂过程中存在局限性。其次，通过监测前体，早期发现故障，可以提供早期发现损坏和故障的新技术，从而为社会带来好处。它还将通过探索力学过程和地球物理特征之间的联系，为科学提供重大的好处。

One of the most important challenges in rock mechanics is the development of tools and technologies that provide accurate information about damage, i.e. new cracks produced inside the rock mass as a result of activities that change existing conditions. Recent laboratory experiments conducted at Purdue University show that it is possible to detect the formation of new cracks inside a rock by monitoring changes in amplitude of compressional and shear waves propagating through the rock. The experiments have also detected the presence of precursors to failure. These precursors have the form of a dramatic drop of amplitude of transmitted waves, which occurs at stress levels well below the stress at which damage/failure occurs. These findings have the potential of providing a methodology to predict impending failure, to detect new cracks, and to provide information about engineering properties of the new cracks such as stiffness and possibly shear strength. The focus of the project is on the experimental verification of such potential. A comprehensive series of experiments will be performed on pre-cracked anisotropic rock subjected to biaxial and cyclic compressional loads to determine: (1) fracture initiation and coalescence processes in the rock; (2) geophysical signature of these processes, in particular the presence of precursors to damage; and (3) coupling between the mechanical and geophysical response of rock under complex loading. The experiments will be conducted on granite, Austin Chalk Cordova Crème, a soft rock that exhibits seismic anisotropy, and sandstone. The work is multi-disciplinary as it combines the expertise of the two principal investigators in fracturing in brittle materials and in geophysical methods applied to fractured rock. The potential for impact of the research in science and society is very high. First, the work will be instrumental in improving our ability to scrutinize the interior of the rock for the presence of cracks and to infer engineering properties of the cracks. This is an important problem that limits advancements in fields such as rock mechanics, stiff soils, and other materials because of the limitations that exist in observing cracking processes under complex loading in the interior of geomaterials. Second, the early detection of failure, by monitoring precursors, may bring benefits to society by providing new technologies to detect damage and failure early. It will also provide a significant benefit to science by probing the link between mechanics processes and geophysical signatures.