CPT-Based Characterization of Intermediate Soils

评估中间土的性质和强度，如粉砂、粘砂、砂质粉砂、砂质粘土和低塑性粉砂，仍然是岩土工程和地质工程中最普遍和最不确定的挑战之一。技术文献中充满了估算清洁砂和沉积粘土强度（例如，排水和不排水，单调和循环）的程序，但它们对中间土壤的扩展往往缺乏健全的理论基础，并且涉及砂和粘土数据的经验插值，而中间土壤的直接数据很少。本研究将通过开发和验证一个基于力学的框架来直接解决这一不足，该框架用于建立锥体穿透阻力、原位应力、状态参数和特定土壤特性（如单调强度和循环阻力比（CRR））之间的相互关系，该框架使用实验室元素测试、锥体穿透数值模拟和离心机模型测试相结合。实验室测试，包括极限压缩，直接简单剪切和三轴，将用于表征九种不同的土壤混合物的特性，跨越广泛的土壤级配和细粒塑性。大应变锥突过程将在FLAC中通过实施任意朗朗日-欧拉（ALE）重网格技术和使用广义本构模型MIT-S1来模拟，后者已被证明可以准确地模拟从砂土到中间土到粘土的土壤行为。将对所有土壤混合物进行数值模拟，在对公布的数据集进行验证后。采用飞行中锥体测深和动态震动进行的离心机模型试验将进一步验证锥体穿透的数值模拟，在实验室元件试验的基础上对预期的循环强度提供独立确认，并提供现场动态响应以及相关的动态和永久地面变形的数据。然后，实验和数值模拟数据将用于开发和评估锥体穿透试验数据与土壤特性之间的各种功能相互关系。这项研究将直接解决基于力学的框架的基本需求，以推进和改变从锥贯入试验数据估计中间土壤强度和其他特性的方式。这项工作将通过整合实验室、离心机和数值模拟组件来解决以前没有系统解决的问题，从而促进理解和知识。潜在的发现将适用于广泛的岩土和地质问题，包括与建立在或由中间土壤建造的任何土结构或土木基础设施系统的静力和地震反应有关的问题。基于科学的广义锥体解释方法有可能改变研究生院和专业课程提供的技术培训，并减少在面对工程不确定性时在实践中采用的昂贵的保守主义。这项研究将有助于研究生的发展，为他们在学术界或工业界的成功职业生涯提供广泛的综合训练，使K-12学生接触岩土和地震工程的各个方面，并为一群高中教师提供地球科学模块的培训，以满足他们的课程需求。

Evaluating properties and strengths of intermediate soils, such as silty sands, clayey sands, sandy silts, sandy clays, and low-plasticity silts, remains one of the most pervasive and uncertain challenges in geotechnical and geological engineering. Technical literature is full of procedures for estimating strengths (e.g., drained and undrained, monotonic and cyclic) of clean sands and sedimentary clays, but their extension to intermediate soils often lacks a sound theoretical basis and involves empirical interpolation of data from sands and clays with little direct data for intermediate soils. This research will directly address this deficiency by developing and validating a mechanics-based framework for establishing inter-relationships between cone penetration resistance, in-situ stresses, state parameter, and specific soil properties such as monotonic strengths and cyclic resistance ratios (CRR) using a combination of laboratory element tests, numerical simulations of cone penetration, and centrifuge model testing. Laboratory tests, including limiting compression, direct simple shear, and triaxial, will be used to characterize the properties of nine different soil mixtures spanning a broad range of soil gradations and fines plasticity. The large-strain process of cone penetration will be modeled in FLAC by implementing an Arbitrary Langrangian-Eulerian (ALE) remeshing technique and using the generalized constitutive model MIT-S1, the latter of which has been shown to accurately model the behavior of soils ranging from sands, to intermediate soils, to clays. Numerical simulations will be performed for all soil mixtures, after validation against published data sets. Centrifuge model tests with in-flight cone soundings and dynamic shaking will enable further validation of the numerical simulations of cone penetration, provide independent confirmation of cyclic strengths expected on the basis of the laboratory element tests, and provide data on dynamic site response and the associated dynamic and permanent ground deformations. The experimental and numerical simulation data will then be used to develop and evaluate various functional inter-relationships between the cone penetration test data and soil properties. This research will directly address the essential need for a mechanics-based framework to advance and transform the way intermediate soil strengths and other properties are estimated from cone penetration test data. The work will advance understanding and knowledge by integrating laboratory, centrifuge, and numerical simulation components to address a topic that has not previously been systematically addressed. The potential findings will be applicable across a broad spectrum of geotechnical and geological problems, including issues associated with the static and seismic responses of any earth structure or civil infrastructure system founded on, or constructed of, intermediate soils. A science-based generalized cone interpretation method has the potential to transform the technical training provided in graduate schools and professional courses, and reduce costly conservatisms adopted in the face of engineering uncertainty in practice. The study will contribute to the development of graduate students with broad integrative training that equips them for successful careers in academia or industry, exposure K-12 students to aspects of geotechnical and earthquake engineering, and provide training for a group of high school teachers on earth science modules that address their curricular needs.