In Situ Characterization and Dynamic Response of Well-Graded Coarse-Grained Soils

基础设施（如水坝、隧道、桥梁）的开发和重新评估建立在、穿透或由天然和/或人造砾石（即大颗粒）土壤组成的基础设施面临着一个持续的挑战，即确定它们的工程特性，以及它们在地震荷载下的表现。这些不确定性导致工程师做出过于保守的设计假设，这可能导致新设计或对现有结构进行改造，单个项目（例如水坝）的成本可能超过1亿美元。该项目将使用数值模拟以及实验室和离心机模型尺度实验来提高我们对这些土壤作为工程材料在受到静态和动态载荷时的行为的理解，并开发一个新的框架，使工程师能够在表征和设计中考虑粒度和土壤级配的影响。项目结果还可能产生超出常规岩土工程领域的影响，并可能应用于其他颗粒材料的表征，包括采矿废料、岩石填筑物、铸造砂、地外土壤（如火星）、农业谷物、药品和食品。综合教育、多样性和推广活动的重点是增加岩土工程中代表性不足的群体的参与和成功，范围从研究生的发展到中学生的推广。砂砾土的表征和性能预测是一个长期存在的工程挑战，因为土壤的大颗粒尺寸使得传统尺寸的原位穿透仪、采样器和实验室设备的数据高度不确定。因此，很少有研究考察颗粒尺寸和土壤级配对穿透阻力、单调和剪切行为或动态工程响应的影响，也没有进行综合的综合研究。现场案例历史表明，这些材料存在问题，岩土工程界缺乏必要的设计工具，无法在与特征更好的砂和粘土相当的水平上进行设计和分析。本项目将使用实验室、数值和离心机模拟工具，系统地研究土壤级配对不同空间尺度下单调和循环行为以及渗透率表征的影响。这四项研究任务解决了等级对以下方面的影响：(1)临界状态框架内的单调应力-剪胀行为；(2)超孔隙压力产生、应变积累和液化触发方面的循环行为；(3)穿透-粒度对CPT尖端阻力测量的影响；(4)水平和倾斜地面条件下系统对动态载荷的响应。仔细选择天然冲积土沉积物，可以制备一套差到好分级的土壤混合物，实验室和离心机实验可以在D50和CU的系统控制下进行，而其他变量（即形状和矿物学）几乎保持不变。这项工作计划的基础是一项广泛的试点研究，该研究已核实了计划的方法并产生了初步结果。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The development and re-evaluation of infrastructure (e.g. dams, tunnels, bridges) founded upon, penetrating through, or comprised of natural and/or man-made gravelly (i.e. large particle) soils face a persistent challenge with respect to determining their engineering properties, and how they will perform under earthquake loading. These uncertainties lead engineers to make overly-conservative design assumptions that can result in new designs or retrofits of existing structures that can cost in excess of $100M for a single project (e.g. dams). This project will use numerical simulations along with laboratory and centrifuge model-scale experiments to improve our understanding of how these soils behave as engineering materials when subjected to static and dynamic loading, and to develop a new framework that enables engineers to account for the effects of particle size and soil gradation in characterization and design. The project results may also have impacts beyond the conventional geotechnical engineering domain, with potential applications to characterization of other particulate materials including mining waste materials, rock fills, foundry sands, extraterrestrial soils (e.g. Mars), agricultural grains, and pharmaceutical and food products. The integrated education, diversity, and outreach activities are focused on increasing the participation and success of underrepresented groups in geotechnical engineering and range from the development of graduate students to outreach to middle school children. The characterization and performance prediction of gravelly soils is a long-standing engineering challenge due to the soil's large particle sizes rendering data from conventional sized in situ penetrometers and samplers and laboratory devices highly uncertain. Thus, very few studies exist where the effect of particle size and soil gradation on either penetration resistance, monotonic and shearing behavior, or dynamic engineering response have been examined, and no comprehensive, integrated study has been performed where both effects are integrated. Field case histories show these materials to be problematic and the geotechnical community lacks the design tools necessary to perform design and analysis at a level on par with better-characterized sands and clays. This project will systematically address the influence of soil gradation on monotonic and cyclic behavior and on penetrometer characterization at different spatial scales using a suite of laboratory, numerical, and centrifuge modeling tools. The four research tasks address the effects of gradation on the: (1) monotonic stress-dilatancy behavior within a critical state framework, (2) cyclic behavior in terms of excess pore pressure generation, strain accumulations, and liquefaction triggering, and (3) penetrometer-to-particle size effects on CPT tip resistance measurements, and (4) system response to dynamic loading under level- and sloping-ground conditions. The careful selection of a natural alluvial soil deposit allows preparation of a suite of poorly- to well-graded soil mixtures on which laboratory and centrifuge experiments can be performed with systematic control over D50 and CU while other variables (i.e. shape and mineralogy) are held practically constant. The work plan is based on an extensive pilot study that has verified the planned approach and produced initial results.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.