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Inherent particle properties such as size, shape, gradation, surface roughness and mineralogy govern the mechanical behavior of coarse-grained soils. Obtaining a detailed understanding of soil behavior requires parametrization of the individual effects of these properties; however, isolating these effects is a challenge in experimental studies. The advances in 3D printing technology provide the ability to generate artificial sand- and gravel-sized particles with independent control over their size, shape, and gradation. This paper summarizes the strength and stiffness behavior of specimens composed of 3D printed (3DP) particles. Specifically, results of triaxial compression and bender element tests on 3DP sands are provided and compared to corresponding results on the natural sands. The 3DP sands show characteristic behaviors of natural sands, such as dependence on effective stress and stress-dilatancy. However, the 3DP soils are more compressible due to the smaller stiffness of the constituent polymeric material. The results show a decrease in critical state friction angle (φ′cs) and an increase in shear wave velocity (Vs) as the particle roundness and sphericity are increased, in agreement with published trends for natural soils. The agreement in trends highlights the potential for investigations using 3DP soils to extend the understanding of soil behavior. 

Site characterization activities, such as Cone Penetration Testing (CPT), Pressuremeter Testing (PMT), and Dilatometer Testing (DMT), can be compromised due to challenges associated with equipment mobilization. This situation is common at locations such as the toe of dams, dense urban environments, deep water, and extraterrestrial bodies. This research uses bio-inspiration to develop a probe that can penetrate itself into the subsurface, eliminating the need for a drill rig to provide the reaction mass. This probe uses an adaptation employed by razor clams, worms, and caecilians where a body section is radially expanded to form an anchor which generates the reaction force needed to penetrate the soil. This paper presents a Discrete Element Modeling (DEM) study of the self-penetration process of this probe. Analysis of soil stress states indicates that the probe configuration influences its self-penetration ability. Specifically, the distance between the anchor and the tip affects the interaction between these probe parts due to principal stress rotation and arching. The results indicate that self-penetration is achievable in medium-dense coarse-grained soil by bio-inspired probes with smaller anchor-tip spacings and provide useful information for the design of future probe prototypes. 

The standard of practice when assessing the seismic performance of well graded sands, is to assume the response is similar to poorly graded clean sands, which comprise the majority of the liquefaction case history database. Using the 9-m radius centrifuge at UC Davis, an experiment was designed to elucidate the system-level liquefaction triggering response for a poorly graded and well graded sand. The experiment consisted of two identical 10-degree slopes positioned side-by-side in the same model container, with one slope constructed with a well graded sand and the other with a poorly graded sand. The D10 grain size was the similar for both gradations and therefore the permeability was comparable. The slopes were dry pluviated to the same relative density of Dr=63%, while the absolute densities were different. The dynamic response of both slopes was similar up until liquefaction triggering, with both sands reaching excess pore pressure ratios close to unity within 1-2 cycles of loading. Following the onset of liquefaction, the well graded sand exhibited strong dilative tendencies and embankment deformations attenuated rapidly during successive loading cycles, while the poorly graded sand embankment continued to deform. This study demonstrates that the posttriggering response of well graded and poorly graded sands differ due to their different absolute densities and dilatancies for the same relative density. It is expected that findings from this research will lead to a more rational accounting of gradation properties in the evaluation of and design for liquefaction effects, as well as the interpretation of case histories.