This project concerns the utilization of 3D printed particle analogs for the fundamental study of coarse-grained soil behavior. These synthetic analogs will address the pervasive challenge in geotechnical engineering caused by the fact that soils are natural materials whose properties are defined by their geologic history, and whose behavior depends on dozens of variables, including particle morphology and size, gradation, and soil state. Development of an interpretation framework, consisting of normalization of the compression and shear responses based on the stiffness of the particles constituent material stiffness, will allow for quantitative study of the response of soils comprised of different materials. It will also allow for validation of results from numerical simulations (e.g. Discrete Element Modeling, DEM). This research: (i) provides the ability to systematically and independently control particle properties of soil analogs, which can transform current research capabilities to study aspects of soil behavior that are important for many applications, such as seepage, pollutant transport, bacterial and fungal growth, erosion, bearing capacity, interface friction, and earth pressures, (ii) facilitates the trans-disciplinary transfer of knowledge among researchers from different disciplines within engineering and the sciences, such as chemical, mechanical and material science engineering and physics, who investigate phenomena in different granular materials such as soils, powders, and grains, (iii) promotes use of 3D printing in research to transform current experimental research techniques within geotechnical engineering, and (iv) increases the involvement of Hispanic students through the entire educational track by training teachers from local middle schools and providing research opportunities to undergraduate students.
Qualitative understanding of soil behavior has been achieved by many researchers through experiments on different soils or soil analogs, Discrete Element Modeling (DEM) simulations, or advanced imaging techniques. The two major barriers that have deterred the construction of quantitative understanding using these tools are: (i) the inability of current experimental methods to systematically change one characteristic of natural soil particles, while keeping the others unchanged (affecting interpretation of studies on natural soils), and (ii) the lack of a framework that allows for study of behaviors independently from differences in constituent material properties (affecting interpretation of studies on soil analogs). The hypothesis of this research project is that the response of 3D printed soil analogs can provide direct and quantitative understanding of the response of natural soils. The effects of particle contact deformation are quantified in particle- and element-scale 1D compression tests, and the coupled effect of particle contact and soil skeleton deformation are characterized in triaxial compression shear tests. These experimental insights, in combination with a stiffness-based normalization scheme that accounts for differences in constituent material properties, comprise a framework that allows for direct comparison of the response of natural and analog soils that is only influenced by particle characteristics and soil state. The developed 3D printed soil analogs and interpretation framework will allow for systematic and independent prescription of particle shape, surface roughness, and size for the detailed study of the behavior of coarse-grained soils. This will advance the understanding of the influence of particle constituent material stiffness on the compression and shear response of soils at the particle- and element-scales, and incorporate the effect of particle stiffness on the framework of critical state soil mechanics.