A micro finite-element model for soil behaviour: experimental evaluation for sand under triaxial compression

Nadimi, Sadegh; Fonseca, J.; Andò, Edward; Viggiani, Gioacchino

doi:10.1680/jgeot.18.t.030

Cited by 16 publications

(5 citation statements)

References 41 publications

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“…Note that limited data for granular assemblies, based on DEM simulations (e.g. Barreto Gonzalez, 2009) or a combination of X-ray computed tomography and micro-finite element analysis (Nadimi et al, 2020) report inter-particle forces between 3 and 6 N at confining pressures of 100 kPa, which suggests that forces between 40 N and 150 N represent stress levels between 1 MPa and 3 MPa, found in pile end bearing or underneath high earth dams.…”

Section: Testing Proceduresmentioning

confidence: 99%

Evolution of surface roughness of single sand grains with normal loading

2022

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The surfaces of soil grains are not perfectly smooth especially examined at small scale. In geotechnical engineering, surface roughness has been found to be able to influence the interparticle friction angle at micro scale and small-strain stiffness at macro scale. However, the quantity and quality of the studies on surface roughness of natural soils are still limited. In this study, the evolution of surface roughness of natural sand grains with increasing normal load was investigated by a single particle compression apparatus. Thirty Leighton Buzzard sand (LBS) grains coarser than 2.36 mm were tested, and the surface roughness was measured before and after compression by an optical interferometer. The deformations of the asperities and of the bulk of the sand grains in the vicinity of the contact were mapped. Three stages were identified as the normal load increased: (1) plastic deformation of the asperities, (2) asperities and bulk plastic deformation and, (3) bulk only plastic deformation. At very small normal load, only the asperities were found to deform plastically, and the surface roughness of the sand grains decreases due to the flattening of the asperities. Within this regime, the loaddisplacement relationship of LBS grains under compression could be simulated by the modified Hertz model which takes surface roughness into consideration. With increasing normal load, the bulk of the sand grains began to yield near the contact. The geometry of the surfaces of LBS grains in contact with the loading platen is the main factor that influences the plastic deformation of the bulk. Different from the plastic deformation of the asperities, the plastic deformation of the bulk could both smoothen and roughen the surfaces. When plastic deformation of the bulk occurred, both Hertz and modified Hertz theory could not predict the load and displacement relationship of sand grains. Through analysing the cumulative distributions of surface roughness of thirty LBS grains at different normal loads by the Weibull function, the surface roughness was found to decrease dramatically with increasing normal load at first and then tend to be constant.

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Section: Testing Proceduresmentioning

confidence: 99%

Evolution of surface roughness of single sand grains with normal loading

2022

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“…A major focus of this research is on whether root growth induces compaction in the immediate soil of the rhizosphere, or an increase in porosity [6,[11][12][13]. X-ray micro-computed tomography (µCT) was employed by several research groups to reveal the micro-structure of geomaterials [14,15] and specifically to study soil-root interaction [12,16,17].…”

Section: Introductionmentioning

confidence: 99%

How Do Roots Interact with Layered Soils?

et al. 2022

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Vegetation alters soil fabric by providing biological reinforcement and enhancing the overall mechanical behaviour of slopes, thereby controlling shallow mass movement. To predict the behaviour of vegetated slopes, parameters representing the root system structure, such as root distribution, length, orientation and diameter, should be considered in slope stability models. This study quantifies the relationship between soil physical characteristics and root growth, giving special emphasis on (1) how roots influence the physical architecture of the surrounding soil structure and (2) how soil structure influences the root growth. A systematic experimental study is carried out using high-resolution X-ray micro-computed tomography (µCT) to observe the root behaviour in layered soil. In total, 2 samples are scanned over 15 days, enabling the acquisition of 10 sets of images. A machine learning algorithm for image segmentation is trained to act at 3 different training percentages, resulting in the processing of 30 sets of images, with the outcomes prompting a discussion on the size of the training data set. An automated in-house image processing algorithm is employed to quantify the void ratio and root volume ratio. This script enables post processing and image analysis of all 30 cases within few hours. This work investigates the effect of stratigraphy on root growth, along with the effect of image-segmentation parameters on soil constitutive properties.

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“…In particular, the number, area and orientation of interparticle contacts are coveted fabric quantities that may be retrieved from XCT data. These parameters can then be used to, for example, analyse the micromechanical behaviour of geomaterials [ 8 , 9 , 10 ] and inform or assess computer modelling methods [ 11 , 12 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

On Acquisition Parameters and Processing Techniques for Interparticle Contact Detection in Granular Packings Using Synchrotron Computed Tomography

2022

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X-ray computed tomography (XCT) is regularly employed in geomechanics to non-destructively measure the solid and pore fractions of soil and rock from reconstructed 3D images. With the increasing availability of high-resolution XCT imaging systems, researchers now seek to measure microfabric parameters such as the number and area of interparticle contacts, which can then be used to inform soil behaviour modelling techniques. However, recent research has evidenced that conventional image processing methods consistently overestimate the number and area of interparticle contacts, mainly due to acquisition-driven image artefacts. The present study seeks to address this issue by systematically assessing the role of XCT acquisition parameters in the accurate detection of interparticle contacts. To this end, synchrotron XCT has been applied to a hexagonal close-packed arrangement of glass pellets with and without a prescribed separation between lattice layers. Different values for the number of projections, exposure time, and rotation range have been evaluated. Conventional global grey value thresholding and novel U-Net segmentation methods have been assessed, followed by local refinements at the presumptive contacts, as per recently proposed contact detection routines. The effect of the different acquisition set-ups and segmentation techniques on contact detection performance is presented and discussed, and optimised workflows are proposed.

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A micro finite-element model for soil behaviour: experimental evaluation for sand under triaxial compression

Cited by 16 publications

References 41 publications

Evolution of surface roughness of single sand grains with normal loading

Evolution of surface roughness of single sand grains with normal loading

How Do Roots Interact with Layered Soils?

On Acquisition Parameters and Processing Techniques for Interparticle Contact Detection in Granular Packings Using Synchrotron Computed Tomography

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