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Detection and Characterization of Precursors to Shear Failure

剪切破坏前兆的检测和表征

基本信息

批准号：
1664562
负责人：
Antonio Bobet
金额：
$ 39.86万
依托单位：
Purdue University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-05-01 至 2022-04-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1664562&HistoricalAwards=false
关键词：
Detection Characterization Precursors Shear Failure

项目摘要

Rocks are difficult materials to characterize and monitor because of their highly heterogeneous nature that leads to complex time- and scale-dependent behavior. Some of the scale-dependent behavior arises from "defects" or "mechanical discontinuities" that exist in the rock. These discontinuities range from the atomic scale, where atom lattices may have irregularities; to the grain scale, where cracks are pervasive at the grain contacts, and up to the regional or continental scale where discontinuities such joints occur from the millimeter scale to faults that range over hundreds of kilometers, such as the North Anatolian fault or the San Andreas fault. One of the most important limitations in research and engineering practice on rocks is our inability to detect accurately the presence of defects and discontinuities inside the rock and to determine the evolution of discontinuities with stress from external agents. Current knowledge of rock damage strongly relies on experiments in the laboratory where direct observations of the surfaces of the rock specimens are made to observe new crack formation. The objective of the research is to establish the relationship between mechanical and geophysical responses of rock under loading to provide a basis for seismic monitoring techniques of rock systems, and to enable the development of analysis tools to evaluate the condition of a rock mass during and after construction. The promise of using elastic wave propagation through fractured rock as an effective monitoring technique is rooted in previous findings by the two Co-PIs who discovered the presence of precursors prior to shear failure of frictional discontinuities, in the form of either distinct maxima or minima in transmitted and reflected waves, respectively. Advances in our ability to detect impending new damage in the form of new cracks or slip along pre-existing discontinuities will prevent failures during construction, ensure long term containment for waste storage, or avoid earthquakes induced by anthropogenic activities such as mining, underground fluid storage or deep wastewater injection.A series of laboratory experiments will be performed to test the hypotheses that these precursors (1) result from a reduction in local fracture specific stiffness in the region monitored by the seismic transducers, and (2) are caused by slip and damage of the asperities, and the hypothesis that failure along the entire discontinuity is the result of progressive slip along the discontinuity. The experiments will consist of subjecting rock joints to biaxial compression loading, and more specifically to direct shear. Digital Image Correlation and geophysical methods will be used to monitor slip and slip failure of the joints, which include wave propagation measurements (both transmitted and reflected waves, as well as other converted modes). The tests will be conducted on granite, limestone or sandstone and shale, each rock having different grain size and anisotropy, and on joints that may be tight or filled with a soil deposit. Both dry and saturated rock specimens will be investigated to determine the geophysical signatures associated with changes in rock saturation, and to identify and quantify the modes that are best-suited for monitoring the potential shear failure of a discontinuity.

岩石是难以表征和监测的材料，因为它们的高度异质性导致复杂的时间和尺度依赖行为。一些尺度依赖行为源于岩石中存在的“缺陷”或“机械不连续性”。这些不连续性的范围从原子尺度，其中原子晶格可能具有不规则性;到颗粒尺度，其中裂纹在颗粒接触处普遍存在，并且直到区域或大陆尺度，其中不连续性例如关节发生从毫米尺度到范围超过数百公里的断层，例如北安纳托利亚断层或圣安德烈亚斯断层。在岩石研究和工程实践中，最重要的限制之一是我们无法准确地检测岩石内部缺陷和不连续性的存在，并确定不连续性随外部应力的演化。目前对岩石损伤的认识主要依赖于实验室中的实验，在实验室中直接观察岩石试样的表面以观察新的裂纹形成。研究的目的是建立岩石在荷载作用下的力学和地球物理响应之间的关系，为岩石系统的地震监测技术提供基础，并使分析工具的开发能够评估施工期间和施工后的岩体状况。作为一种有效的监测技术，使用弹性波传播通过断裂岩石的承诺是植根于以前的调查结果，由两个合作PI谁发现了存在的前体剪切破坏的摩擦不连续性，在形式上的不同的最大值或最小值，在传输和反射波，分别。我们在检测即将发生的新损害（新裂缝或沿着先前存在的不连续性滑动）的能力方面的进步，将防止施工期间的故障，确保废物储存的长期遏制，或避免采矿等人为活动引起的地震，地下流体储存或深层废水注入。将进行一系列实验室实验来检验这些前体（1）由地震传感器监测的区域中的局部断裂比刚度的降低引起，以及（2）由粗糙体的滑动和损坏引起，以及假设沿整个间断沿着的失效是沿间断沿着的渐进滑动的结果。实验将包括使岩石节理承受双轴压缩载荷，更具体地说是直接剪切。数字图像相关和地球物理方法将用于监测接缝的滑动和滑动破坏，其中包括波传播测量（透射波和反射波，以及其他转换模式）。试验将在花岗岩、石灰岩或砂岩和页岩上进行，每种岩石具有不同的粒度和各向异性，并在可能紧密或填充有土壤存款的接缝上进行。将对干燥和饱和岩石样本进行调查，以确定与岩石饱和度变化相关的地球物理特征，并确定和量化最适合监测不连续面潜在剪切破坏的模式。