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56 results on '"One-dimensional compression"'

51. A Study of the Particle-Level Fabric and Morphology of Granular Soils under One-Dimensional Compression Using Insitu X-ray CT Imaging.

Author

Alam, Md Ferdous, Haque, Asadul, and Ranjith, Pathegama Gamage

Subjects
*SOIL granularity, *COMPUTED tomography, *MECHANICAL behavior of materials, *MORPHOLOGY, *MECHANICAL properties of condensed matter
Abstract

The particle morphology and fabric of a granular soil influence its mechanical behavior. This study focuses on the evolution of the particle-level fabric and morphology of a uniformly graded sand sample subjected to one-dimensional compression up to 64 MPa. The microstructural changes with increased stresses were captured using in situ high-resolution X-ray computed tomography (X-ray CT) imaging. The processed images of particles were separated using the Monash Particle Separation Method (MPSM) for subsequent fabric and morphological analyses. The variations of various fabric parameters were studied using the separated particle volumes. New methods of assessing the morphology and crushability of particles were introduced including a comprehensive algorithm for determining coordination number, branch and contact normal vectors. Results of all fabric parameters were analyzed and discussed with reference to observed changes. Potential mechanisms were identified and relevant correlations were developed where warranted. [ABSTRACT FROM AUTHOR]

Published
2018
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52. The evolution of grain-size distribution of sands under 1-D compression

Author

VALORE, Calogero, ZICCARELLI, Maurizio, Valore, C, and Ziccarelli, M

Subjects
Settore ICAR/07 - Geotecnica, one-dimensional compression, characteristic diameter, particle crushing, grain-size distribution
Abstract

Crushing of particles is a fundamental mechanisms leading to deformation of particulate materials at medium and high stresses. As crushing progresses, the grain-size distribution undergoes modifications, causing changes of the porosity, grain-to-grain contacts and of their density (”packing density” and “grain contact”). The main aim of the research is the identification of trends in the modifications of characteristic diameters (D10, D15, D25, etc.) in function of the applied stress s´v. Results of a laboratory research programme on the crushing of dry sands compressed under one-dimensional conditions, at vertical effective stresses ′v up to 120 MPa, are reported in the paper. Tests have been carried out on calcareous bioclastic and on quartz sands, with initial coefficient of uniformity Cu ranging from 1.10 to 1.42. The crushing of bioclastic sand particles is considerable even at low stresses, whilst for quartz sands it becomes appreciable for stresses higher than 10 MPa. It is shown that the evolution of the grain-size distribution of a given sand can be effectively represented by the following relation between the absolute value of the decrement of the generic characteristic diameter Di and ′v: Di= h/(K(1+C e –hlgv)), where C, h, K are parameters depending upon the nature and the initial grain-size distribution of the sand. This Verhulst type relation properly accounts for the existence of an upper limit to Di. The analysis of published data shows that this type of relation also applies for other, quite different, sands.

Published
2009

53. Effect of Particle Morphology on the Deformation Behavior of Sand under Monotonic Loading Conditions

Author

Leib, Alexia Rose

Subjects
Granular Materials, isotropic consolidation, particle shape, triaxial, one-dimensional compression, digital image correlation, Geotechnical Engineering
Abstract

When a projectile hits sand, the projectile places high stresses on the sand surface. Granular materials at high stresses are liable to crushing. The pressure at which crushing occurs depends greatly on particle shape and relative density. These parameters also greatly influence the changes in particle shape and size after crushing. Additionally, projectiles fired at extremely high velocities are preceded by a pressure wave. This pressure wave can crush granular material before the projectile ever touches the surface. If the sand has been crushed and its inherent particle properties changed before projectile impact, the projectile may not behave as expected. Therefore, it is imperative to understand a wide variety of strength parameters in order to understand the mechanics of sands with different morphology. Furthermore, when performing experiments to obtain strength parameters, it is important to understand the limitations of these experiments. Particle size distribution methods such as standard sieve tests, imaging analysis, and light scattering techniques all involve a level of bias particle size bias in the data acquisition process. Additionally, standard triaxial testing assumes constant strain throughout the specimen based on overall displacement of the specimen during testing. This is an invalid assumption as strain localization occurs very early during testing and causes strain concentrations near the center of the specimen.

Published
2015

54. Investigating the effects of particle shape on normal compression and overconsolidation using DEM

Author

de Bono, John P., McDowell, Glenn R., de Bono, John P., and McDowell, Glenn R.

Abstract

Discrete element modelling of normal compression has been simulated on a sample of breakable two-ball clumps and compared to that of spheres. In both cases the size effect on strength is assumed to be that of real silica sand. The slopes of the normal compression lines are compared and found to be consistent with the proposed equation of the normal compression line. The values of the coefficient of earth pressure at rest K0,nc are also compared and related to the critical state fiction angles for the two materials. The breakable samples have then been unloaded to establish the stress ratios on unloading. At low overconsolidation ratios the values of K0 follow a well-established empirical relationship and realistic Poisson ratios are observed. On progressive unloading both samples head towards passive failure, and the values of the critical state lines in extension in q–p' space are found to be consistent with the critical state angles deduced from the values of K0 during normal compression. The paper highlights the important role of particle shape in governing the stress ratio during both normal compression and subsequent overconsolidation.

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55. Investigating the effects of particle shape on normal compression and overconsolidation using DEM

Author

de Bono, John P., McDowell, Glenn R., de Bono, John P., and McDowell, Glenn R.

Abstract

Discrete element modelling of normal compression has been simulated on a sample of breakable two-ball clumps and compared to that of spheres. In both cases the size effect on strength is assumed to be that of real silica sand. The slopes of the normal compression lines are compared and found to be consistent with the proposed equation of the normal compression line. The values of the coefficient of earth pressure at rest K0,nc are also compared and related to the critical state fiction angles for the two materials. The breakable samples have then been unloaded to establish the stress ratios on unloading. At low overconsolidation ratios the values of K0 follow a well-established empirical relationship and realistic Poisson ratios are observed. On progressive unloading both samples head towards passive failure, and the values of the critical state lines in extension in q–p' space are found to be consistent with the critical state angles deduced from the values of K0 during normal compression. The paper highlights the important role of particle shape in governing the stress ratio during both normal compression and subsequent overconsolidation.

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56. Investigating the effects of particle shape on normal compression and overconsolidation using DEM

Author

de Bono, John P., McDowell, Glenn R., de Bono, John P., and McDowell, Glenn R.

Abstract

Discrete element modelling of normal compression has been simulated on a sample of breakable two-ball clumps and compared to that of spheres. In both cases the size effect on strength is assumed to be that of real silica sand. The slopes of the normal compression lines are compared and found to be consistent with the proposed equation of the normal compression line. The values of the coefficient of earth pressure at rest K0,nc are also compared and related to the critical state fiction angles for the two materials. The breakable samples have then been unloaded to establish the stress ratios on unloading. At low overconsolidation ratios the values of K0 follow a well-established empirical relationship and realistic Poisson ratios are observed. On progressive unloading both samples head towards passive failure, and the values of the critical state lines in extension in q–p' space are found to be consistent with the critical state angles deduced from the values of K0 during normal compression. The paper highlights the important role of particle shape in governing the stress ratio during both normal compression and subsequent overconsolidation.

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