Examination of the Strength and Dilatancy of Granular Materials using 3D Printed Soil

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The determination of the strength and stiffness of sands and gravels is a very important component of the design and construction of many civil engineering structures such as building and bridge foundations, levees, earth dams and retaining walls. Geotechnical engineers know that strength and stiffness are a function of grain shape and texture, as well as the density of the soil and the pressure it is subjected to. However, natural sands and gravels vary in mineralogy, surface roughness, size distribution, and particle shape making it very difficult to gain a clear understanding of how these variables affect the soil?s engineering properties. This research seeks to apply a novel technology, 3D printing, to a classical soil mechanics problem to reexamine soil strength in a way that is not possible with natural soils. 3D printed particles maintain the same material and surface properties even when the particle shape or size distribution is varied. This feature allows for the direct influence of particle shape to be examined. Laboratory experiments on 3D printed granular particles will be used to refine current theories of soil behavior. Being able to better predict the behavior of sands and gravels on a description of shape would greatly advance the state-of-art in the fields of soil mechanics, geotechnical engineering, pavement materials, and material handling processes. In addition, the use of 3D printed soil provides a synergistic approach to teaching fundamental soil behavior at the undergraduate and graduate levels. Critical state soil mechanics provides a useful framework for analyzing soil behavior, but the need for large soil databases and the lack of a unique relationship between dilatancy and strength hinders its more-wide acceptance among practitioners and undergraduate soil mechanics classes. Because the critical state shearing angle is mostly dependent on mineralogy, the peak angle of shearing resistance depends on a dilatancy-related component of strength, and thus it depends on shape. This research tests the hypothesis that 3D printed particles can be used as an analog granular soil to investigate the relationship between dilatancy and strength by systematically varying shape while keeping the material properties the same. Not only will the experimental data be useful to demonstrate this relationship, but it will also be instrumental in the validation of discrete element method (DEM) models which can be used to examine the particle-scale response. Understanding the fundamental behavior in a dilatancy context will contribute to an increased understanding of numerous, more complex geotechnical problems including: liquefaction, pile side friction, bearing capacity, slope stability, and in situ testing (Cone Penetrometer Test, Standard Penetration Test).