Natural soil deposits can consist of particles with a wide range of sizes. In current practice,
the assessment of shear strength and stress-dilatancy behavior of coarse-grained soils is based on methods developed for poorly graded sands, without explicit consideration for differences in gradation. This paper investigates the influence of the range of particle sizes on the monotonic shear strength and the stress-dilatancy response of poorly- to well-graded soils. Using the 3D discrete element method (DEM), the applicability of commonly used sand-based stress-dilatancy frameworks is assessed for a range of gradations. This DEM investigation employs clumps of spheres to accurately simulate the particle shapes on specimens with coefficients of uniformity (CU) varying between 1.9 and 6.9. These specimens were subjected to isotropically consolidated drained triaxial compression at various relative densities and confining stresses with the objective of isolating the effects of particle size distribution from those of particle shape. The peak and critical state shear strengths and the dilatancy responses of the specimens with different gradations are evaluated. For the same state parameter, the results indicate an increase in the shear strength and rate of dilation as the range of particle sizes increases. However, the critical
state line shifts downward, and its slope decreases as CU is increased. The DEM results are
compared to Bolton’s stress-dilatancy relationship to highlight the inadequacies of using clean sand-based frameworks in capturing the behavior of well-graded soils.
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Particle Size Effects on the Strength and Fabric of Granular Media
The reliance on sand-based methods for the characterization and design of gravelly soils is necessitated in part by a limited understanding of how to account for the effects of particle size and distribution. In this paper, particle size effects on the strength and fabric of cohesionless, granular media are investigated using the discrete element method by testing specimens with particle size distributions (PSDs) of differing coefficient of uniformity (CU) and mean grain size (d50). Preliminary results show that when all particle shape characteristics are equal, increasing d50 yields equivalent stress-strain responses for the same relative density (DR) and CU. However, when increasing CU, specimens exhibit more dilative tendencies and greater shear strengths. Increasing CU results in more dispersive distributions of contact force, stress, and coordination number. The void ratios associated with minimum and maximum density, and constant volume conditions during shear also decrease with increasing CU.
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- Award ID(s):
- 1916152
- NSF-PAR ID:
- 10158288
- Date Published:
- Journal Name:
- GeoCongress 2020
- Page Range / eLocation ID:
- 349 to 358
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1061/9780784482803.038
