A broad spectrum of well-graded, coarse-grained soils are commonly present in natural
deposits, though characterization of these materials has been approximated using sand-based
engineering methods in liquefaction evaluations. Through combined results of 31 constant stress
direct simple shear and drained triaxial compression tests, this study experimentally investigates
the effect of mean grain size (D50) and gradation (Cu) on the drained monotonic strength and
stress-dilatancy of poorly- to well-graded, coarse-grained soils. Coarse-grained mixtures of
varying D50 and gradations were prepared to relative densities of 20%–75% and tested under a
range of overburden stresses. Results are analyzed in terms of the frictional resistance and
dilative contributions to the shear strength of soils with varying gradations, as compared to clean
sands, using different shearing modes. It is shown that (1) increased gradation of soils increases
the peak shear strength and frictional resistance due to a greater initial rate of dilation exhibited
in well-graded, coarse-grained soils; and (2) current stress-dilatancy relationships underestimate
the dilative behavior of well-graded test materials.
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Effect of Particle Size Distribution on Monotonic Shear Strength and Stress-Dilatancy of Coarse-Grained Soils
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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- Award ID(s):
- 1916152
- NSF-PAR ID:
- 10462062
- Date Published:
- Journal Name:
- Geo-Congress 2023
- Volume:
- GSP 340
- Page Range / eLocation ID:
- 302-312
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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