- Award ID(s):
- Publication Date:
- NSF-PAR ID:
- Journal Name:
- Journal of geotechnical and geoenvironmental engineering
- Page Range or eLocation-ID:
- Sponsoring Org:
- National Science Foundation
More Like this
Effect of Particle Size Distribution on Monotonic Shear Strength and Stress-Dilatancy of Coarse-Grained SoilsNatural 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, andmore »
Well-graded soils can be found in nature and in engineered structures, such as dams and embankments. Prediction of their behavior is still an engineering challenge in part due to the lack of data in the literature, arguably due to difficulties associated in testing these soils in the laboratory and in situ. Particularly, there is still debate over the effect of the increased range of particle sizes (i.e., widening gradation) on the shear strength and dilatancy of coarse-grained soils. This paper presents the results of drained and undrained isotropically-consolidated triaxial compression tests on six soil mixes of varying gradation. These soils were sourced from a single natural deposit and selectively sieved and mixed to isolate the effects of gradation from those of particle shape and mineralogy. The results indicate that the critical state lines in void ratio – mean effective stress space move downward as the gradation becomes wider. For the same state parameter, the soils with a wider gradation exhibit greater dilatancy and generate negative excess pore pressures with greater magnitudes than the poorly-graded soils. In drained conditions, the greater dilatancy of the well-graded soils leads to greater peak friction angles, while in undrained conditions it leads to greater undrainedmore »
Strength-dilatancy and critical state behaviours of binary mixtures of graded sands influenced by particle size ratio and fines contentBinary granular soil mixtures, as common heterogeneous soils, are ubiquitous in nature and man-made deposits. Fines content and particle size ratio are two important gradation parameters for a binary mixture, which have potential influences on mechanical behaviours. However, experimental studies on drained shear behaviour considering the whole range of fines content and different particle size ratios are scarce in the literature. For this purpose, we performed a series of drained triaxial compression tests on dense binary silica sand mixtures with 4 different particle size ratios to systematically investigate the effects of fines content and particle size ratio on the drained shear behaviours. Based on these tests, the strength-dilation behaviour and critical state behaviour were examined. It was observed that both fines content and particle size ratio have significant influence on the stress-strain response, the critical state void ratio, the critical state friction angle, the maximum dilation angle, the peak friction angle, and the strength–dilatancy relation. The underlying mechanism for the effects of fines content and particle size ratio was discussed from the perspective of the kinematic movements at particle level.
Effect of Gradation on the Strength and Stress-Dilatancy of Coarse-Grained Soils: A Comparison of Monotonic Direct Simple Shear and Triaxial TestsA 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.
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 responsemore »
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.