CAREER: Promoting a Fundamental Understanding of Post-Liquefaction Response and Deformations: A Next-Generation Analytical and Experimental Methodology

本教师早期职业发展（CAREER）项目的研究目标是开发一个统一的，可扩展的方法，从微观到宏观尺度的土壤液化变形分析。 地震是影响我们社会的最致命和最昂贵的自然灾害之一。 地震期间损失的主要原因之一是由于地震压缩（即地震震动期间非饱和土壤中收缩体积应变的累积）、地面软化或土壤液化而引起的地震诱发位移。 土壤液化工程中的大多数研究都集中在液化“触发”可能性的评估上，然而，在液化引起的变形评估方面还有很多工作要做。 然而，为了设计有效和高效的液化危害缓解技术，需要对液化的发展及其后果有透彻的了解。 该CAREER奖项介绍了下一代3D离散元建模（DEM）和独特的大规模实验的集成，用于了解液化后稳定性和地面变形。 首要的研究目标是确定和量化的物理和环境参数，特别是在微观和细观尺度上影响粒状土壤的循环响应，并将它们与宏观尺度（即现场）的响应和变形。 由于其颗粒性质，土壤对施加的载荷和变形表现出高度复杂的响应。 人们普遍认为，特别是在循环荷载期间，土壤的颗粒性质和颗粒形态（即颗粒纵横比和棱角）主要影响其响应及其相关变形。 本研究将（a）结合CSS室内试验和三维离散元分析，在微观和细观尺度上表征颗粒集合体的颗粒形态，并研究干燥和饱和颗粒土的循环响应，（B）使用三维DEM分析研究循环荷载过程中土壤结构变化和孔隙比重新分布的微观力学方面，以及（c）开发一个用于缩放微观结构的框架。通过模拟文献中报道的选择离心机实验和一个概念验证案例历史，并调查控制过渡到宏观尺度响应的输入模型参数，来研究粒状土壤对宏观尺度（即现场）响应的中尺度（即颗粒-颗粒接触）和细尺度（即颗粒组装）行为。 并行计算的最新进展将被用来减少3D DEM的计算工作量。定制的TST（平移分离表）和12”CSS（循环简单剪切）的实验室设备将被用来表征的颗粒形态的第一次成千上万的颗粒，然后将循环剪切。 大规模的CSS设备可以容纳已知的颗粒总数和颗粒形态的砾石大小的颗粒标本，允许使用3D DEM的颗粒对颗粒的模拟。这种1：1的实验和DEM模拟的方法是尝试首次使用真实的soils.This项目的方法有可能改变土壤液化工程领域提供更可靠的估计液化引起的变形。 更好地了解粒状土在循环荷载作用下对位移的微观响应，可以更好地评估地震荷载作用下土结构的性能，也可以评估关键工程结构（如土石坝、堤坝、港口码头、桥台、桩和桥墩基础）的缓解措施的有效性。 本研究的教育计划的重点是测试的假设，提供一个学术和研究环境丰富的现实生活中的应用和社会相关的例子，将提高女本科生保留在岩土工程。 为此，PI打算（a）通过利用UMich内的项目，向本科女生介绍研究项目，（B）为岩土工程本科课程开发一系列课堂演示、讲义材料和调查问卷，以介绍土木工程项目的实际应用和积极的社会成果，（c）开发一门新的计算地质力学课程。

The research objective of this Faculty Early Career Development (CAREER) project is to develop a unified, scalable approach for soil liquefaction deformation analysis from micro to macro-scale. Earthquakes are among the most deadly and expensive natural disasters affecting our society. One of the leading causes of loss during earthquakes is seismically-induced displacements due to seismic compression (i.e. accrual of contractive volumetric strains in unsaturated soils during earthquake shaking), ground softening or soil liquefaction. The majority of research in soil liquefaction engineering has focused on the assessment of the likelihood of "triggering" of liquefaction, however much remains to be done with regards to the assessment of liquefaction-induced deformations. Yet, to engineer effective and efficient liquefaction hazard mitigation techniques, a thorough understanding of the development of liquefaction and its consequences is needed. This CAREER award presents a next-generation integration of 3D Discrete Element Modeling (DEM) and unique large-scale experiments for understanding post-liquefaction stability and ground deformation. The overarching research goal is to identify and quantify the physical and environmental parameters that affect the cyclic response of granular soils at the micro- and meso-scale particularly and relate them to the macro-scale (i.e. field) response and deformations. Soil exhibits a highly complex response to applied loads and deformations due to its particulate nature. It is widely recognized that especially during cyclic loading, it is this particulate nature of the soil and the particle morphology (i.e. particle aspect ratio and angularity) that mostly affects its response and its associated deformations. This research will (a) characterize particle morphology of granular assemblies and investigate the cyclic response of dry and saturated granular soils at the micro- and meso-scale by combining CSS laboratory tests and 3D DEM analyses, (b) study the micromechanical aspects of soil fabric changes and void ratio redistribution during cyclic loading using 3D DEM analysis and (c) develop a framework for scaling the micro (i.e. particle-to-particle contact) and meso-scale (i.e. particle assembly) behavior of granular soils to the macro-scale (i.e. field) response by simulating select centrifuge experiments reported in the literature and one proof-of-concept case-history, and investigating the input model parameters that control the transition to the macro-scale response. Recent advances in parallel computing will be employed to reduce computational effort of the 3D DEM. A custom-made TST (Translucent Segregation Table) and 12" CSS (Cyclic Simple Shear) laboratory device will be employed to characterize for the first time the particle morphology of thousands of particles that will then be cyclically sheared. The large-scale CSS apparatus can accommodate gravel-size particle specimens of known total number of particles and particle morphology allowing for a particle-to-particle simulation using the 3D DEM. Such a 1:1 approach of experimentation and DEM simulations is attempted for the first time using real soils.This project's approach has the potential to transform the field of soil liquefaction engineering by providing more reliable estimates of liquefaction-induced deformations. A better understanding of the micro-scale response of granular soils under cyclic loading with respect to displacement can lead to a better evaluation of the performance of earthen structures during earthquake loads and also of the assessment of the effectiveness of mitigation measures for critical engineered structures such as earth or rockfill dams, levees, harbor frontages, bridge abutments, and pile and pier foundations. The educational plan of this study focuses on testing the hypothesis that providing an academic and research environment rich in real-life applications and socially relevant examples, will improve female undergraduate student retention in geotechnical engineering. To this effect, the PI intends to (a) introduce undergraduate female students to research projects by capitalizing on programs within UMich, (b) develop a series of in-class presentations, handout materials and questionnaires for the undergraduate course on geotechnical engineering to introduce real-world applications and positive social outcomes from civil engineering projects and (c) develop a new course on Computational Geomechanics.