权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Creep in Shale Across Space and Time

页岩中跨越时空的蠕变

基本信息

批准号：
1914780
负责人：
Ronaldo Borja
金额：
$ 42.18万
依托单位：
Stanford University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-07-01 至 2024-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1914780&HistoricalAwards=false
关键词：
Creep Shale Across Space Time

项目摘要

Shale is a fine-grained sedimentary rock composed of softer materials such as clay and organics, as well as stiffer minerals such as quartz, feldspar, pyrite, and carbonates. It is the most common sedimentary rock on Earth, estimated to represent between 44 and 56 percent of all sedimentary rocks. Unlike crystalline rocks that tend to fracture under deformation, shales can serve as a seal because they are more pliable in the sense that they can undergo significant deformation without breaking. However, they are also known to exhibit significant time-dependent deformation behavior, or creep, that is observed across spatial and temporal scales. The tendency of shale to creep is well correlated with how the softer and stiffer components of this rock share an imposed load. In addition, the reduction in sample volume during creep suggests that this phenomenon is accommodated by compaction of the pore spaces between the solid grains. The latter process can lead to significant ground subsidence that often compromises the integrity and sustainability of civil infrastructures. Using laboratory and numerical modeling techniques, this project will investigate the multiscale creep behavior in shale across space and time. Laboratory experiments include indentation tests to probe the creep behavior at the nanometer scale, and triaxial tests on cylindrical specimens of rock to investigate creep at the millimeter scale. The combined laboratory experimentation-numerical simulation activities of the project will involve the participation of undergraduate students through summer research. A promotional video of the laboratory tests and numerical simulation results will be produced for recruiting graduate students as well as for outreach.The objective of this project is to capture the creep processes in shale at multiple scales in both space and time. Scale-bridging techniques will be developed linking creep processes at the nanometer, micrometer, and millimeter scales. Shale will be modeled as a mixture of softer matter (clay, organics) and stiffer matter (quartz, feldspar, pyrite, carbonates) whose creep behavior is described by Viscoplasticity Theory. A framework developed from a previous NSF project entitled "Creep in Shale at Submicron Scale" will be employed to quantify creep of the softer matter from nano-indentation tests and creep of the shale matrix from micro-indentation tests. Hold periods during nano- and micro-indentation will be timed to fully delineate the expected exponential decay of creep indentation. Validation of the model will be conducted from triaxial creep tests at the millimeter scale. Indentation creep tests typically last no more than a few minutes, whereas triaxial creep tests last for several hours and even days. This research will reconcile this very large discrepancy in the time scales for these two experiments. Throughout the course of testing, the microstructure of the material will be imaged using Transmission X-ray Microscopy (TXM), micro-Computed Tomography (mCT), and conventional Computed Tomography (CT) to delineate the spatial heterogeneity of shale at different scales. Creep of shale is one of the most intriguing and challenging phenomena in rock engineering because of the highly heterogeneous nature of this material. The combined experimental-numerical investigation will accommodate heterogeneity and will lead to better understanding and more realistic modeling of creep processes in shale at multiple scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

页岩是一种细粒沉积岩，由粘土和有机物等较软的物质以及石英、长石、黄铁矿和碳酸盐等较硬的矿物组成。它是地球上最常见的沉积岩，估计占所有沉积岩的 44% 至 56%。与在变形下容易破裂的结晶岩石不同，页岩可以起到密封作用，因为它们更柔韧，可以经历显着变形而不会破裂。然而，它们也表现出显着的时间依赖性变形行为或蠕变，这是在空间和时间尺度上观察到的。页岩的蠕变趋势与该岩石中较软和较硬的成分如何分担所施加的载荷密切相关。此外，蠕变过程中样品体积的减少表明这种现象是通过压缩固体颗粒之间的孔隙空间来调节的。后一个过程可能会导致严重的地面沉降，这通常会损害民用基础设施的完整性和可持续性。该项目将利用实验室和数值模拟技术，研究页岩在空间和时间上的多尺度蠕变行为。实验室实验包括用于探测纳米尺度蠕变行为的压痕试验，以及用于研究毫米尺度蠕变的圆柱形岩石样本三轴试验。该项目的实验室实验与数值模拟相结合的活动将由本科生通过暑期研究参与。我们将制作实验室测试和数值模拟结果的宣传视频，用于招收研究生和宣传。该项目的目标是在空间和时间的多个尺度上捕获页岩的蠕变过程。将开发连接纳米、微米和毫米尺度蠕变过程的尺度桥接技术。页岩将被建模为较软物质（粘土、有机物）和较硬物质（石英、长石、黄铁矿、碳酸盐）的混合物，其蠕变行为由粘塑性理论描述。美国国家科学基金会之前的一个名为“亚微米级页岩蠕变”的项目开发的框架将用于量化纳米压痕测试中软质物质的蠕变和微压痕测试中页岩基质的蠕变。纳米和微米压痕期间的保持时间将被定时，以充分描绘蠕变压痕的预期指数衰减。模型的验证将通过毫米级的三轴蠕变试验进行。压痕蠕变试验通常持续不超过几分钟，而三轴蠕变试验则持续几个小时甚至几天。这项研究将解决这两个实验在时间尺度上的巨大差异。在整个测试过程中，将使用透射X射线显微镜（TXM）、微型计算机断层扫描（mCT）和传统计算机断层扫描（CT）对材料的微观结构进行成像，以描绘不同尺度的页岩的空间异质性。由于页岩材料的高度异质性，页岩蠕变是岩石工程中最有趣和最具挑战性的现象之一。实验与数值相结合的研究将适应异质性，并将在多个尺度上更好地理解页岩蠕变过程并进行更现实的建模。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。