Role of hydromechanical properties of plant roots in unsaturated soil shear strength

Leung, Anthony Kwan; Boldrin, David; Karimzadeh, Ali Akbar; Bengough, A. Glyn

doi:10.3208/jgssp.v07.020

Cited by 5 publications

(2 citation statements)

References 17 publications

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“…Plant roots permeated to the soil matrix form a soil-root composite and resist shearing by mobilising the roots' tensile or/and flexural properties and the soil-root interface friction (Gray and Barker 2004;Schwarz et al 2010). In addition to mechanical reinforcement, recent research has demonstrated that the removal of soil moisture through the process of plant transpiration and root-water uptake induces soil matric suction, which in turn increases the soil shear strength (Leung et al 2017(Leung et al , 2019Boldrin et al 2018Boldrin et al , 2020Switala et al 2018;Mahannopkul and Jotisankasa 2019;Ni et al 2019;Yildiz et al 2019) To reveal and understand the root reinforcement mechanisms, it is vital to identify the stress paths relevant to slope failure. Figure 1 shows a marginally stable vegetated slope and three major stress states in which their major principal stresses are rotating along a slip surface from the slope crest to toe.…”

Section: Introductionmentioning

confidence: 99%

Monotonic and cyclic behaviour of root-reinforced sand

et al. 2021

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Plant roots are known to provide mechanical reinforcement to soils upon shearing and seismic loading. However, the effects of different stress paths on root reinforce-ment are unclear. Moreover, whether, and how, roots provide resistance to soil lique-faction upon cyclic loading have rarely been studied. The objective of this study is to conduct a series of undrained triaxial tests to investigate the monotonic and cyclic behaviour of rooted sand. Roots of vetiver grass (Chrysopogon zizanioides L), which has been advocated for use in shallow slope stabilisation purposes, were used for testing. The root diameters ranged between 0.3 to 1.5 mm, while the root volume ra-tios were 0.23%, 0.45% and 0.67%. It was discovered that the root reinforcement ef-fect was anisotropic and path-dependent. Along the extension path when the major principal stress was perpendicular to the predominant root orientation, the root-induced increase in soil friction angle was approximately 10o. This increase was much greater than the case along the compression path where the change was min-imal. The presence of roots prevented the limited flow failure (which occurred in the unreinforced sand), and the failure mode of root-reinforced soil switched to cyclic mobility. The liquefaction resistance was improved with an increase in root volume, and this improvement was more remarkable at higher cyclic stress ratios.

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Section: Introductionmentioning

confidence: 99%

Monotonic and cyclic behaviour of root-reinforced sand

et al. 2021

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“…e results showed that the shear strength of a root-soil complex with significant lateral roots and vertical roots increased more than that of a root-soil complex with only lateral roots. Leung et al [31] conducted experiments on six trees of a similar age under light and no-light conditions and found that root water absorption had a relatively small contribution to plant soil-induced suction, and root water absorption had a relatively small impact on the soil water retention curve. Veylon et al [32] used the direct shear box test method to study three tree species of reforestation on slopes in Yunnan and quantified the influence of soil water content on soil reinforced by plant roots.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on Shear Resistance of Carex‐Root‐Fibered Soil

Wang

Zhao

Sun

2021

Advances in Civil Engineering

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Carex shows strong vitality, adaptability, and performance with regard to soil consolidation and slope protection but is often disregarded as a weed. This study proposes to turn this so-called weed into treasure, using its characteristics to protect the slope. We studied the interaction between the carex roots and soil and compared it to other types of grass. To understand the interaction between the carex roots and soil, this study investigated the tensile properties of the carex root fibers. The effects of fiber content, humidity, distribution, and soil moisture content on the relationship between the shear strength and vertical pressure of the soil were analyzed using a direct shear test. Furthermore, the cohesion and internal friction angle were used to evaluate the shear strength of the root-fibered soil based on Mohr–Coulomb’s law. The results showed that the smaller the diameter, the shorter the length, and the greater the quantity and the lower the humidity of the root fibers, the higher the tensile strength of root fibers. In addition, the soil strength could be improved by the joint action of the roots and the soil. With an increase in the root fiber content and humidity, the soil moisture content decreased, whereas the shear strength of the carex-root-fibered soil increased. Here, four kinds of root fiber distributions, namely, “glyph,” “herringbone,” “eccentric,” and “vertical,” were chosen to study the shear strength of the root-fibered soil. The results showed that “glyph” root fiber distribution had the highest shear strength, while the shear strength decreased for the others.

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Shearing behaviour of vegetated soils with growing and decaying roots

et al. 2022

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Plant roots affect the soil shear strength, but the temporal dynamics of roots such as growth and decay due to different mortality means have rarely been considered. This study investigates the effects of root growth and decay on the changes in root biomechanical properties and the shearing behaviour of vegetated soils. Columns of compacted soils were grown with a grass species, Cynodon dactylon. The grass was grown for 6 months, followed by burning or herbicide applications to introduce root decay. The top part of each column was used for direct-shear tests, whilst the roots collected from the bottom part were used for the measurements of root tensile and chemical properties. The vegetated soils displayed greater shear strength and larger dilatancy, which were attributable to the growth-induced increase in the root cellulose content and thus the root tensile strength and modulus. Root decay, upon burning or herbicide use, caused significant declines in the root tensile properties, which translated to the reductions in soil dilatancy and soil shear strength lower than those of the fallow soil. Herbicide use introduced a much faster and significant loss of root reinforcement than burning because of the more severe decay and loss of root biomechanical properties.

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Role of hydromechanical properties of plant roots in unsaturated soil shear strength

Cited by 5 publications

References 17 publications

Monotonic and cyclic behaviour of root-reinforced sand

Monotonic and cyclic behaviour of root-reinforced sand

Experimental Study on Shear Resistance of Carex‐Root‐Fibered Soil

Shearing behaviour of vegetated soils with growing and decaying roots

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