In situ root identification through blade penetrometer testing – part 2: field testing

Meijer, G. J.; Bengough, A. Glyn; Knappett, Jonathan; Loades, Kenneth; Nicoll, Bruce

doi:10.1680/jgeot.16.p.204

Cited by 13 publications

(12 citation statements)

References 32 publications

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“…Assuming that the tensile strength of root analogues was similar to the bending strength, it was hypothesised that differences between analogues largely stemmed from different values of

τ_{u} E_{t}^{- 1}

p_{u} E_{t}^{- 1}

(which spanned several orders of magnitude; see Figure ) and root slenderness L d −1 . All tests using wooden and ABS root analogues had small values for dimensionless groups

p_{u} d^{- 1} E_{t}^{- 1}

and

τ_{u} E_{t}^{- 1}

compared with cases with real tree and woody shrub roots in field conditions measured by Meijer et al() Tests using rubber root analogues in shallow, dry sand were closer to field conditions; the small tensile stiffness of rubber compared with real roots was offset by the small soil resistances. All root analogues tests were short compared with typical root length‐diameter relationships.…”

Section: Discussionmentioning

confidence: 77%

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Analysis of coupled axial and lateral deformation of roots in soil

Meijer

Wood

Knappett

et al. 2018

Num Anal Meth Geomechanics

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Summary Plant roots can help to stabilise slopes. Existing analytical models to predict their mechanical contribution are however limited: they typically focus on the ultimate limit state, employ various empirical factors, and ignore much of the underlying root‐soil interaction. A new model was developed based on large deflection Euler‐Bernoulli elastic beam theory that can be used to study the mobilisation of root strength under various loading conditions (direct shear and pull‐out). Both lateral and axial loading of the root by the soil were incorporated, based on existing methodologies for foundation piles (p‐y and t‐z curves). The model is able to take the key parameters into account (root biomechanical properties, root architectural properties, and soil properties) while remaining quick to solve using a numerical boundary value problem solver. The model was compared with experimental direct shear test data using various root analogues (rubber, plastic, and wood) in dry sand with various densities and effective stress levels and was able to accurately predict the measured shear force‐displacement behaviour. Comparison with experimentally measured pull‐out force‐displacement curves using rubber and wooden root analogues with various architectures in dry and partially saturated sands was also satisfactory. In the future, this model can aid with addressing long‐standing problems in the root‐reinforcement community: quantifying the effect of (sequential) mobilisation of root strength in direct shear, the effect of the angle at which the root crosses a shear plane, the effect of root topology on root‐reinforcement or the effect of root bending, and root shear shear forces on root‐reinforcement.

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“…Assuming that the tensile strength of root analogues was similar to the bending strength, it was hypothesised that differences between analogues largely stemmed from different values of

τ_{u} E_{t}^{- 1}

p_{u} E_{t}^{- 1}

(which spanned several orders of magnitude; see Figure ) and root slenderness L d −1 . All tests using wooden and ABS root analogues had small values for dimensionless groups

p_{u} d^{- 1} E_{t}^{- 1}

and

τ_{u} E_{t}^{- 1}

Section: Discussionmentioning

confidence: 77%

“…Field data based on estimations of p u and τ u using cone penetration tests (CPT) and shear vane testing in clayey silt rooted with Pedunculate oak and sandy silt rooted with Sitka spruce. E t was measured by uniaxial tension tests [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Discussionmentioning

confidence: 99%

Analysis of coupled axial and lateral deformation of roots in soil

Meijer

Wood

Knappett

et al. 2018

Num Anal Meth Geomechanics

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“…Root segments are modelled as linear elastic, spring supported beams following Euler-Bernoulli beam theory. Roots are flexible compared to structural piles with Young's moduli of around 100 MPa [7] and tensile strains to failure of around 15-20% [8]. Therefore, conventional beam theory needs to be extended to account for large deformations.…”

Section: Model Descriptionmentioning

confidence: 99%

Root branching affects the mobilisation of root-reinforcement in direct shear

et al. 2019

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The contribution of roots to the mechanical behaviour of soil has typically only been studied for the ultimate limit state. In these approaches, roots are typically modelled as straight and unbranched structures. This approach overlooks the fact that roots may have to deform significantly to mobilise their strength, a process that will be influenced by root architecture effects such as branching, amongst others. Sequential mobilisation of roots affects the peak root-reinforcement, thus differences in mobilisation are important to consider when quantifying root-reinforcement. In this paper, the effect of root branching was modelled using a large-deformation Euler-Bernoulli beam-spring model. The effect of soil was incorporated using non-linear springs, similar to p-y and t-z theory used for foundation piles. By connecting multiple beams together (i.e. applying appropriate linked boundary conditions at root connection points) the effect of branching could be analysed. A soil displacement profile corresponding with direct shear loading was then imposed and the response of the root analysed. It was shown that adding branches led to a quicker mobilisation of root-reinforcement. Branches increased the axial resistance to root displacement and changed the shape of the deformed roots. The presence of branching counteracted root slippage, and thus increased reinforcement. Larger branching densities increased this effect. This analysis demonstrated that the architecture of the root system has a strong effect on the mobilisation of root strength, which directly affects the maximum amount of reinforcement the roots will provide. Future modelling of root-reinforcement, both at the ultimate and serviceable limit state, should account for this effect.

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“…Mickovski et al, 2009;Loades et al, 2010Loades et al, , 2013Boldrin et al, 2017a, b;Leung et al, 2017), largescale investigation into the global slope performance and detection of the failure mechanism of vegetated slopes under rainfall or earthquakes using either centrifuge modelling or numerical modelling approaches (e.g. Sonnenberg et al, 2010Sonnenberg et al, , 2011Liang et al, 2015, development of analytical models for predicting the deformation response of vegetated slopes , and development of rapid in situ testing technique for determining rooted soil properties (Meijer et al, 2016(Meijer et al, , 2017.…”

Section: Introductionmentioning

confidence: 99%