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

本学院早期职业发展(CALEAR)项目的研究目标是开发一种从微观到宏观的统一的、可扩展的土壤液化变形分析方法。地震是影响我们社会的最致命和代价最高的自然灾害之一。地震期间造成损失的主要原因之一是地震压缩(即地震期间非饱和土壤收缩体积应变的累积)、地面软化或土壤液化引起的地震引起的位移。土壤液化工程的大部分研究都集中在“触发”液化的可能性的评估上，然而，在评估液化引起的变形方面仍有很多工作要做。然而，为了设计出有效和高效的液化危险缓解技术，需要对液化的发展及其后果有一个透彻的了解。这一职业奖展示了3D离散元素建模(DEM)和独特的大型实验的下一代集成，以了解液化后的稳定性和地面变形。总体研究目标是识别和量化在微观和细观尺度上影响颗粒土循环响应的物理和环境参数，并将它们与宏观尺度(即场)响应和变形联系起来。由于土壤的颗粒性质，它对外加载荷和变形的响应非常复杂。人们普遍认为，尤其是在循环加载期间，土壤的这种颗粒性质和颗粒形态(即颗粒长径比和角度)对其响应和相关变形的影响最大。这项研究将(A)表征颗粒团聚体的颗粒形态，并结合CSS实验室试验和三维DEM分析，在微观和细观尺度上研究干燥和饱和颗粒土的循环响应，(B)利用三维DEM分析研究循环加载过程中土体组构变化和孔隙率重分布的微观力学方面，以及(C)通过模拟文献中报道的离心机试验和一个概念验证案例，并研究控制向宏观尺度响应转变的输入模型参数，建立一个将颗粒土的微观(即颗粒接触)和细观(即颗粒聚集)行为尺度化为宏观(即现场)响应的框架。并行计算的最新进展将被用来减少三维DEM的计算量。将使用定制的TST(半透明分离表)和12“CSS(循环简单剪切)实验室设备来首次表征数千个颗粒的颗粒形态，然后这些颗粒将被循环剪切。该大型css装置可以容纳已知颗粒总数和颗粒形态的砾石大小的颗粒样品，从而允许使用3D DEM进行颗粒到颗粒的模拟。这种1：1的实验和DEM模拟方法是第一次尝试使用真实的土壤。该项目的方法有可能通过提供更可靠的液化引起的变形估计来改变土壤液化工程领域。更好地了解颗粒土在循环荷载作用下的微尺度位移响应，可以更好地评估土结构在地震荷载作用下的性能，也可以评估关键工程结构(如土石坝、堤坝、港湾、桥台、桩和桥墩基础)的缓解措施的有效性。这项研究的教育计划侧重于检验这样一个假设，即提供一个丰富的现实应用和社会相关实例的学术和研究环境，将提高女本科生在岩土工程领域的留存率。为此，国际土木工程学会打算：(A)利用密歇根大学的项目，向本科生介绍研究项目；(B)为岩土工程本科课程开发一系列课堂陈述、讲义材料和问卷，介绍土木工程项目在现实世界中的应用和积极的社会成果；以及(C)开发一门新的计算岩土力学课程。

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.