Modelling of stress transfer in root-reinforced soils informed by four-dimensional X-ray computed tomography and digital volume correlation data

Vegetation enhances soil shearing resistance through water uptake and root reinforcement. Analytical models for soils reinforced with roots rely on input parameters that are difficult to measure, leading to widely varying predictions of behaviour. The opaque heterogeneous nature of rooted soils results in complex soil–root interaction mechanisms that cannot easily be quantified. The authors measured, for the first time, the shear resistance and deformations of fallow, willow-rooted and gorse-rooted soils during direct shear using X-ray computed tomography and digital volume correlation. Both species caused an increase in shear zone thickness, both initially and as shear progressed. Shear zone thickness peaked at up to 35 mm, often close to the thickest roots and towards the centre of the column. Root extension during shear was 10–30% less than the tri-linear root profile assumed in a Waldron-type model, owing to root curvature. Root analogues used to explore the root–soil interface behaviour suggested that root lateral branches play an important role in anchoring the roots. The Waldron-type model was modified to incorporate non-uniform shear zone thickness and growth, and accurately predicted the observed, up to sevenfold, increase in shear resistance of root-reinforced soil.

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Comparison of the Mechanical Behaviour of Standard and Auxetic Foams by X-ray Computed Tomography and Digital Volume Correlation

Strain ◽

10.1111/str.12053 ◽

2013 ◽

Vol 49 (6) ◽

pp. 467-482 ◽

Cited By ~ 26

Author(s):

F. Pierron ◽

S. A. McDonald ◽

D. Hollis ◽

J. Fu ◽

P. J. Withers ◽

...

Keyword(s):

Computed Tomography ◽

Mechanical Behaviour ◽

Digital Volume Correlation ◽

X Ray ◽

X Ray Computed

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Quantitative 3D strain analysis in analogue experiments simulating tectonic deformation: Integration of X-ray computed tomography and digital volume correlation techniques

Journal of Structural Geology ◽

10.1016/j.jsg.2013.07.011 ◽

2013 ◽

Vol 55 ◽

pp. 127-149 ◽

Cited By ~ 42

Author(s):

J. Adam ◽

M. Klinkmüller ◽

G. Schreurs ◽

B. Wieneke

Keyword(s):

Computed Tomography ◽

Strain Analysis ◽

Tectonic Deformation ◽

Digital Volume Correlation ◽

X Ray ◽

X Ray Computed ◽

Correlation Techniques ◽

Analogue Experiments

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Quantitative Evaluation of Soil Structure and Strain in Three Dimensions under Shear Using X-ray Computed Tomography Image Analysis

Journal of Imaging ◽

10.3390/jimaging7110230 ◽

2021 ◽

Vol 7 (11) ◽

pp. 230

Author(s):

Shintaro Nohara ◽

Toshifumi Mukunoki

Keyword(s):

Computed Tomography ◽

Image Analysis ◽

Shear Zone ◽

Soil Structure ◽

Three Dimensions ◽

Image Correlation ◽

Ct Scanner ◽

Zone Formation ◽

X Ray ◽

X Ray Computed

The objective of this study is to quantitatively evaluate the soil structure behavior when under shear stress to understand the mechanism of shear zone formation using a micro-focus X-ray computed tomography (CT) scanner to visualize the internal samples without causing disturbance. A new image-analysis method was proposed to systematically evaluate the particle length and direction by fitting the particle as an ellipsoid. Subsequently, a direct shear experiment was conducted on soil materials, and shear band was scanned using a micro-focus X-ray CT scanner. After validating the proposed method, the soil structure was evaluated in the shear zone via image analysis on the CT images. Furthermore, the strain inside the specimen was evaluated using digital image correlation. The results showed that a partial change in the particle direction occurred when the volume expansion inside the shear zone exceeded the peak. In addition, the width of the shear zone was ~7.1 times the median grain size of the sand used; however, the region exhibiting a change in the direction of the particles was narrow and confined to the vicinity of the shear plane.

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Understanding the mechanisms of root-reinforcement in soils: soil shear tests using X-ray computed tomography and digital volume correlation

E3S Web of Conferences ◽

10.1051/e3sconf/20199212009 ◽

2019 ◽

Vol 92 ◽

pp. 12009

Author(s):

Daniel Bull ◽

Ian Sinclair ◽

Fabrice Pierron ◽

Tiina Roose ◽

Joel Smethurst

Keyword(s):

Computed Tomography ◽

Three Dimensions ◽

Digital Volume Correlation ◽

Strain Component ◽

Multiscale Models ◽

Root Reinforcement ◽

Length Scales ◽

X Ray ◽

Shearing Resistance ◽

X Ray Computed

Soil containing plant roots may be expected to exhibit a greater shearing resistance compared with the same ‘unreinforced’ soil, providing enhanced stability and effective erosion control, particularly for earth slopes. To be able to rely on the improved shearing resistance and stiffness of root-reinforced soils, it is important to understand and quantify the effectiveness of root reinforcement. This requires sophisticated multiscale models, building understanding at different length scales, from individual soil-root interaction through to full soil-profile or slope scale. One of the challenges with multiscale models is ensuring that they are representative of real behaviour, and this requires calibration to detailed high-quality experiments. The focus of the work presented was to capture and quantify root-reinforcement behaviour and associated soil and root deformation mechanisms during direct shear at the macroscopic to millimetre length scales. A novel shear box was developed to operate within a large-scale X-ray computed tomography (CT) scanner. Tests were interrupted to be scanned at a series of shear displacements from 0-20 mm to capture the chronology of behaviour in three-dimensions. Digital volume correlation (DVC) was applied to the CT dataset to obtain full-field 3D displacement and strain component information. The study demonstrates feasibility of the technique and presents preliminary DVC results.

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Mechanisms of root reinforcement in soils: an experimental methodology using four-dimensional X-ray computed tomography and digital volume correlation

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2019.0838 ◽

2020 ◽

Vol 476 (2237) ◽

pp. 20190838

Author(s):

D. J. Bull ◽

J. A. Smethurst ◽

I. Sinclair ◽

F. Pierron ◽

T. Roose ◽

...

Keyword(s):

Computed Tomography ◽

Three Dimensional ◽

Shear Loading ◽

Soil Reinforcement ◽

Experimental Methodology ◽

Digital Volume Correlation ◽

X Ray ◽

Reinforced Soils ◽

Multi Scale ◽

X Ray Computed

Vegetation on railway or highway slopes can improve slope stability through the generation of soil pore water suctions by plant transpiration and mechanical soil reinforcement by the roots. To incorporate the enhanced shearing resistance and stiffness of root-reinforced soils in stability calculations, it is necessary to understand and quantify its effectiveness. This requires integrated and sophisticated experimental and multi-scale modelling approaches to develop an understanding of the processes at different length scales, from individual root–soil interaction through to full soil-profile or slope scale. One of the challenges with multi-scale models is ensuring that they sufficiently closely represent real behaviour. This requires calibration against detailed high-quality and data-rich experiments. This study presents a novel experimental methodology, which combines in situ direct shear loading of a willow root-reinforced soil with X-ray computed tomography to capture the three-dimensional chronology of soil and root deformation within the shear zone. Digital volume correlation (DVC) analysis was applied to the computed tomography dataset to obtain full-field three-dimensional displacement and strain information. This paper demonstrates the feasibility and discusses the challenges associated with DVC experiments on root-reinforced soils.

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