Methods to measure the mechanical behaviour of tree roots: A review

Giadrossich, Filippo; Schwarz, Massimiliano; Cohen, Denis; Cislaghi, Alessio; Vergani, Chiara; Hubble, Thomas; Phillips, Chris; Stokes, Alexia

doi:10.1016/j.ecoleng.2017.08.032

Cited by 105 publications

(90 citation statements)

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“…Root breakage, on the other hand, is usually intended as a breakage near the clamping point. However, it is interesting to observe that between these two extreme cases the breakage often occurs at an unpredictable point along the root, as field and laboratory experiments demonstrate (see also Giadrossich et al, 2017), due to weak points along the root, but also because of active earth pressure.…”

Section: Discussionmentioning

confidence: 99%

“…This is one of the main sources of error in the root reinforcement estimation (Giadrossich et al. ). In the following section, we carry out simulations to assess the impact of small roots on root reinforcement on the basis of our findings applied to original data of root distributions and field root pullout tests of Douglas fir.…”

Section: Discussionmentioning

confidence: 99%

“…Soil cohesion and friction angle were obtained by extrapolation from failure points obtained by direct shear tests with normal stress values of 2.7, 6.0, and 12 kPa and fitted by a linear regression (Giadrossich et al. ). The normal stress used was lower than that in the classic geotechnical direct shear test because the magnitude of the normal stress at the failure surface of shallow landslides is only a few kPa.…”

Section: Methodsmentioning

confidence: 99%

“…Pullout tests are one of the most used and important direct tests to assess root reinforcement (Giadrossich et al. ); nonetheless, this type of test represents root extraction from a stable soil, analogous to the scenario where a shallow landslide initiates uphill with respect to the trees. This scenario is rarely encountered in reality: most often, trees are upslope of the tension crack, surrounding the headscarp (e.g., Schmidt et al.…”

Section: Introductionmentioning

confidence: 99%

“…Wu et al, 1979;Gray and Leiser, 1982;Stokes et al, 2009Stokes et al, , 2014. In addition to hydrological effects (e.g., rainfall interception, pore water pressure reduction) the main effect of vegetation on slope stability is the mechanical reinforcement of soils by roots (Sidle and Ochiai, 2006;Stokes et al, 2014;Sidle and Bogaard, 2016;Vergani et al, 2016;Sidle and Ziegler, 2017;Cohen and Schwarz, 2017;Giadrossich et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Large roots dominate the contribution of trees to slope stability

Giadrossich

Cohen

Schwarz

et al. 2019

Earth Surf Processes Landf

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Tree roots provide surface erosion protection and improve slope stability through highly complex interactions with the soil due to the nature of root systems. Root reinforcement estimation is usually performed by in situ pullout tests, in which roots are pulled out of the soil to reliably estimate the root strength of compact soils. However, this test is not suitable for the scenario where a soil progressively fails in a series of slump blocks – for example, in unsupported soils near streambanks and road cuts where the soil has no compressive resistance at the base of the hillslope. The scenario where a soil is unsupported on its downslope extent and progressively deforms at a slow strain rate has received little attention, and we are unaware of any study on root reinforcement that estimates the additional strength provided by roots in this situation. We therefore designed two complementary laboratory experiments to compare the force required to pull the root out. The results indicate that the force required to pull out roots is reduced by up to 50% when the soil fails as slump blocks compared to pullout tests. We also found that, for slump block failure, roots had a higher tendency to slip than to break, showing the importance of active earth pressure on root reinforcement behaviour, which contributes to reduced friction between soil and roots. These results were then scaled up to a full tree and tree stand using the root bundle and field‐measured spatial distributions of root density. Although effects on the force mobilized in small roots can be relevant, small roots have virtually no effect on root reinforcement at the tree or stand scale on hillslopes. When root distribution has a wide range of diameters, the root reinforcement results are controlled by large roots, which hold much more force than small roots. © 2019 John Wiley & Sons, Ltd.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%