CPT-Based Characterization of Intermediate Soils

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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.