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Different particle properties, such as shape, size, surface roughness, and constituent material stiffness, affect the mechanical behavior of coarse-grained soils. Systematic investigation of the individual effects of these properties requires careful control over other properties, which is a pervasive challenge in investigations with natural soils. The rapid advance of 3D printing technology provides the ability to produce analog particles with independent control over particle size and shape. This study examines the triaxial compression behavior of specimens of 3D printed sand particles and compares it to that of natural sand specimens. Drained and undrained isotropically-consolidated triaxial compression tests were performed on specimens composed of angular and rounded 3D printed and natural sands. The test results indicate that the 3D printed sands exhibit stress-dilatancy behavior that follows well-established flow rules, the angular 3D printed sand mobilizes greater critical state friction angle than that of rounded 3D printed sand, and analogous drained and undrained stress paths can be followed by 3D printed and natural sands with similar initial void ratios if the cell pressure is scaled. The results suggest that some of the fundamental behaviors of soils can be captured with 3D printed soils, and that the interpretation of their mechanical response can be captured with the critical state soil mechanics framework. However, important differences in response arise from the 3D printing process and the smaller stiffness of the printed polymeric material.

Graphic abstract

Artificial sand analogs were 3D printed from X-ray CT scans of sub-rounded and sub-angular natural sands. Triaxial compression tests were performed to characterize the strength and dilatancy behavior as well as critical staste parameters of the 3D printed sands and to compare it to that exhibited by the natural sands.

 

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. 

This paper presents the prospect of 3D printing technology to generate artificial soil analogs with the goal of modeling the mechanical behavior of coarse-grained soils. 3D X-ray CT scans of natural angular and rounded sand particles have been used to generate angular and rounded particle analogs using the polyjet 3D printing technology. A comparison of the scanned natural sand particles and the 3D printed particles demonstrates the ability of 3D printing technology to reproduce the shape and size of the sand particles. The results of oedometer compression tests on the angular and rounded natural and 3D printed particles are used to demonstrate the effect of constituent material (i.e. quartz versus polymer) stiffness on the measured soil compressibility and investigate the normalization of the response using the Hertz contact theory. The results provided in this paper also include comparison of the small-strain moduli–mean effective stress relationship obtained for the natural and 3D printed soils. This paper illustrates the potential use of 3D printed analogs to model the mechanical behavior of coarse-grained soils and identifies future research needs for implementation of the proposed normalization scheme within the critical state soil mechanics framework. 

This paper presents the initial developments of a framework for modeling the compression behavior of coarse-grained soil using 3D printed particle analogs. This framework consists of a newly developed normalization scheme for 1-D compression response based on Hertz contact theory. The scheme normalizes the differences in stiffness of the natural and 3D printed particles’ constituent materials. To explore the capabilities of the proposed framework, this paper presents results of 1D compression tests on assemblies composed of spherical particles of constituent materials with Young’s moduli that span over two orders of magnitude (steel, glass and 3D printed resin). These initial results indicate that the stress-strain behavior of the assemblies can be normalized to be independent of constituent material stiffness. The presented framework can be useful for modeling the behavior of natural soil by testing representative 3D printed analogs, provided that the different aspects of the soils, such as particle shape, size, surface roughness and gradation are properly reproduced.