scholarly journals Modeling root reinforcement using root-failure Weibull survival function

2013 ◽  
Vol 10 (3) ◽  
pp. 3843-3868 ◽  
Author(s):  
M. Schwarz ◽  
F. Giadrossich ◽  
D. Cohen
Keyword(s):  
Mechanical Properties ◽  
Slope Stability ◽  
Root Distribution ◽  
Survival Function ◽  
Root Diameter ◽  
Root Turnover ◽  
Diameter Class ◽  
Stability Calculation ◽  
Root Reinforcement ◽  
Root Strength

Abstract. Root networks contribute to slope stability through complicated interactions that include mechanical compression and tension. Due to the spatial heterogeneity of root distribution and the dynamic of root turnover, the quantification of root reinforcement on steep slope is challenging and consequently the calculation of slope stability as well. Although the considerable advances in root reinforcement modeling, some important aspect remain neglected. In this study we address in particular to the role of root strength variability on the mechanical behaviors of a root bundle. Many factors may contribute to the variability of root mechanical properties even considering a single class of diameter. This work presents a new approach for quantifying root reinforcement that considers the variability of mechanical properties of each root diameter class. Using the data of laboratory tensile tests and field pullout tests, we calibrate the parameters of the Weibull survival function to implement the variability of root strength in a numerical model for the calculation of root reinforcement (RBMw). The results show that, for both laboratory and field datasets, the parameters of the Weibull distribution may be considered constant with the exponent equal to 2 and the normalized failure displacement equal to 1. Moreover, the results show that the variability of root strength in each root diameter class has a major influence on the behavior of a root bundle with important implications when considering different approaches in slope stability calculation. Sensitivity analysis shows that the calibration of the tensile force and the elasticity of the roots are the most important equations, as well as the root distribution. The new model allows the characterization of root reinforcement in terms of maximum pullout force, stiffness, and energy. Moreover, it simplifies the implementation of root reinforcement in slope stability models. The realistic quantification of root reinforcement for tensile, shear and compression behavior allows the consideration of the stabilization effects of root networks on steep slopes and the influence that this has on the triggering of shallow landslides.

scholarly journals Modeling root reinforcement using a root-failure Weibull survival function

2013 ◽  
Vol 17 (11) ◽  
pp. 4367-4377 ◽  
Author(s):  
M. Schwarz ◽  
F. Giadrossich ◽  
D. Cohen
Keyword(s):  
Mechanical Properties ◽  
Slope Stability ◽  
Root Distribution ◽  
Survival Function ◽  
Root Diameter ◽  
Root Turnover ◽  
Diameter Class ◽  
Root Reinforcement ◽  
Root Strength ◽  
Steep Slopes

Abstract. Root networks contribute to slope stability through complex interactions with soil that include mechanical compression and tension. Due to the spatial heterogeneity of root distribution and the dynamics of root turnover, the quantification of root reinforcement on steep slopes is challenging and consequently the calculation of slope stability also. Although considerable progress has been made, some important aspects of root mechanics remain neglected. In this study we address specifically the role of root-strength variability on the mechanical behavior of a root bundle. Many factors contribute to the variability of root mechanical properties even within a single class of diameter. This work presents a new approach for quantifying root reinforcement that considers the variability of mechanical properties of each root diameter class. Using the data of laboratory tensile tests and field pullout tests, we calibrate the parameters of the Weibull survival function to implement the variability of root strength in a numerical model for the calculation of root reinforcement (RBMw). The results show that, for both laboratory and field data sets, the parameters of the Weibull distribution may be considered constant with the exponent equal to 2 and the normalized failure displacement equal to 1. Moreover, the results show that the variability of root strength in each root diameter class has a major influence on the behavior of a root bundle with important implications when considering different approaches in slope stability calculation. Sensitivity analysis shows that the calibration of the equations of the tensile force, the elasticity of the roots, and the root distribution are the most important steps. The new model allows the characterization of root reinforcement in terms of maximum pullout force, stiffness, and energy. Moreover, it simplifies the implementation of root reinforcement in slope stability models. The realistic quantification of root reinforcement for tensile, shear and compression behavior allows for the consideration of the stabilization effects of root networks on steep slopes and the influence that this has on the triggering of shallow landslides.

Root strength comparison between early and late successional trees in a subtropical forest

2020 ◽  
Author(s):  
Cang-Wei Chen ◽  
Guo-Zhang M. Song ◽  
Li-Wan Chang ◽  
Chien-Jui Ko ◽  
Hsin-Tien Lee ◽  
...  
Keyword(s):  
Slope Stability ◽  
Tree Species ◽  
Survival Function ◽  
Root Diameter ◽  
Single Root ◽  
Pull Out ◽  
Daunting Task ◽  
Root Strength ◽  
Successional Species ◽  
Central Taiwan

<p><strong>ABSTRACT    </strong></p><p>Slope stability of forested areas is often determined by tree root strength. After landslides, the early successional species emerged first, followed by the late successional species. This study aimed to examine whether tree root strength varies as tree species change along with the succession sequence. The study site is in the Lienhuachi Experimental Forest in central Taiwan, where multiple landslides happened in 2008. Three dominant early (Mallotus paniculatus, Sapium discolor, and Schefflera octophylla) and three late successional species (Cryptocarya chinensis, Engelhardtia roxburghiana, and Randia cochinchinensis) were sampled to conduct the single-root-pull-out tests in the field. Root strength which varies with root diameters was estimated with the Root Bundle Model with the root-failure Weibull survival function (RBMw). Results showed that the overall root strength of the early successional tree species were higher than that of late successional species only when root diameter was lower than 5.44 mm. However, among the six species, the root strength of Sapium discolor, an early successional species, was highest and the species with the lowest root strength was a late successional species (Engelhardtia roxburghiana). To precisely estimate tree effects on slope stability, our results highlighted the need to collect root strength data specifically for each species, even though it will be a daunting task for areas rich in tree diversity.</p><p><strong>Keyword: landslide, Root Bundle Model, vegetation succession </strong></p>

Effects of root tensile force and diameter distribution variability on root reinforcement in the Swiss and Italian Alps

2014 ◽  
Vol 44 (11) ◽  
pp. 1426-1440 ◽  
Author(s):  
C. Vergani ◽  
M. Schwarz ◽  
D. Cohen ◽  
J.J. Thormann ◽  
G.B. Bischetti
Keyword(s):  
Mechanical Properties ◽  
Root Distribution ◽  
Dominant Role ◽  
Tensile Force ◽  
Root Diameter ◽  
Diameter Distribution ◽  
Mountain Range ◽  
Data Set ◽  
Root Reinforcement ◽  
Wide Range

Root reinforcement is considered to be one of the most important factors contributing to the stability of vegetated hillslopes; however, its estimation is still challenging because of the spatial variability of root distribution and root mechanical properties. This work uses the root bundle model to assess the sensitivity of root-reinforcement estimation to the variability in both root mechanical properties and root distribution. We used a large data set of root tensile tests and root distributions of an important alpine species, Picea abies (L.) Karst., collected in a wide range of altitudinal and climatic ranges on both north and south sides of the alpine mountain range. The results demonstrate that the site-specific characterization of mechanical properties and root distribution is fundamental for the quantification of root reinforcement at the stand scale. Root diameter distribution plays a dominant role in influencing the root-reinforcement model’s output; however, in contrast with results from other works, differences in root diameter–force functions are significant and cannot be ignored. Model results also show that coarse roots contribute significantly more to the reinforcement of soil than fine roots, underlying the need of additional data for roots with diameters larger than 5 mm.

scholarly journals Effect of Oriental beech root reinforcement on slope stability (Hyrcanian Forest, Iran)

2014 ◽  
Vol 60 (No. 4) ◽  
pp. 166-173 ◽  
Author(s):  
E. Abdi
Keyword(s):  
Tensile Strength ◽  
Slope Stability ◽  
Root Distribution ◽  
Factor Of Safety ◽  
Power Relationship ◽  
Strength Increase ◽  
Hyrcanian Forest ◽  
Reinforcement Effect ◽  
Root Reinforcement ◽  
Oriental Beech

Vegetation significantly affects hillslope mechanical properties related to shallow landslides and slope stability. The objective of this study was to investigate and quantify the effect of Oriental beech root reinforcement on slope stability. A part of Hyrcanian forest in northern Iran was selected for the study area. To do the research, the Wu model (WM) was used and data related to the distribution and tensile strength of Oriental beech roots were collected. Root distribution was assessed using the concept of the root area ratio and trenching method. Laboratory tensile tests were conducted on fresh roots for strength characteristics. The factor of safety was calculated for two different soil thicknesses (1 and 2 m) and slope gradients between 10 and 45&deg;. The results showed that the root distribution generally decreased with increasing soil depth and the mean root strength value was 38.23 &plusmn; 1.19 MPa for 0.35&ndash;5.60 mm diameter range. The results verified a power relationship between tensile strength and root diameter. The reinforcement effect (C<sub>r</sub>) decreased with depth and the strongest reinforcement effect was in the second soil layer (10&ndash;20 cm) which showed a shear strength increase of 1.47 kPa. The increased factor of safety due to the presence of roots in one- and two-metre soil thicknesses was 27&ndash;44% and 15&ndash;26%, respectively. The improvement effect of roots was increased with increasing slope gradient and shallower soil thicknesses. &nbsp; &nbsp;

scholarly journals Tree-roots control of shallow landslides

2017 ◽  
Author(s):  
Denis Cohen ◽  
Massimiliano Schwarz
Keyword(s):  
Slope Stability ◽  
Shallow Landslide ◽  
Shallow Landslides ◽  
Tree Roots ◽  
Root Reinforcement ◽  
Apparent Cohesion ◽  
Root Strength ◽  
Tension And Compression ◽  
Weak Zones ◽  
Landslide Triggering

Abstract. Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. These observations contradict the common assumptions used in present models. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the self-organized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. The model is driven by root data of Norway spruce obtained from laboratory and field measurements. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of these forces is comparable to the slope-perpendicular tensile forces. In these cases, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, hillslopes form a crack parallel to the slope near its top. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, large roots, greater than 20 mm, are too few too contribute significantly to root reinforcement. Omitting roots larger than 8 mm predicted a landslide when none should have occurred. Intermediate roots (5 to 20 mm) appear to contribute most to root reinforcement and should be included in calculations. To fully understand the mechanisms of shallow landslide triggering requires a complete re-evaluation of the traditional apparent-cohesion approach that does not reproduce the incremental loading of roots in tension or in compression. Our model shows that it is important to consider the forces held by roots in a way that is entirely different than done thus far. Our work quantifies the contribution of roots in tension and compression which now finally permits to analyze more realistically the role of root reinforcement during the triggering of shallow landslides.

scholarly journals Minimum representative root distribution sampling for calculating slope stability in Pinus radiata D.Don plantations in New Zealand

2020 ◽  
Vol 50 ◽  
Author(s):  
Filippo Giadrossich ◽  
Massimiliano Schwarz ◽  
Michael Marden ◽  
Roberto Marrosu ◽  
Chris Phillips
Keyword(s):  
Water Quality ◽  
New Zealand ◽  
Slope Stability ◽  
Pinus Radiata ◽  
Root Distribution ◽  
Soil Loss ◽  
Mean Value ◽  
Management Tools ◽  
Root Reinforcement ◽  
Characteristic Value

Background: Rainfall-triggered shallow landslides on steep slopes cause significant soil loss and can be hazards for property and people in many parts of the world. In New Zealand’s hill country, they are the dominant erosion process and are responsible for soil loss and subsequent impacts on regional water quality. Use of wide-spaced trees and afforestation with fast growing conifers are the primary land management tools in New Zealand to help control erosion and improve water quality. To decide where to implement erosion controls in the landscape requires determining the most susceptible places to these processes and models that incorporate how trees reinforce soils to understand if, and when, such treatments become effective. Methods: This paper characterises the mechanical properties of Pinus radiata D.Don roots (the common tree species used for afforestation in New Zealand) by means of field pullout tests and by measuring the root distribution at 360 degrees around trees. The Root Bundle Model (RBM) was used to calculate the root reinforcement. Statistical analysis was carried out to assess the statistical reduction coefficients of root reinforcement that depend on the number of measurements, used in geotechnical analysis to reduce the mean value of a parameter to a so-called characteristic value. Results: We show that to reach an effective level of root reinforcement, trees of 0.5 m DBH require a density of about 300 trees per hectare. Trees of this size are about 30 years of age across many sites and have generally reached the recommended conditions for clear-fell harvesting. The analysis of variance shows that 4 trees are the minimum number to be excavated to obtain sufficient root information to obtain less than 5% of error with a 95% of probability on the estimation of a design value of root reinforcement in accord with geotechnical standards. Conclusions: We found that the variability of lateral and basal root reinforcement does not limit the implementation of vegetation in slope stability models for Pinus radiata. We adopt for the first time the concept of a minimum sampling requirement and characteristic value, similarly to what is assumed for the value of effective soil cohesion in geotechnical guidelines for slope stability calculations.

A new tool to accurately calculate root reinforcement: the Root Bundle Model software RBM++

2020 ◽  
Author(s):  
Ilenia Murgia ◽  
Denis Cohen ◽  
Filippo Giadrossich ◽  
Gian Franco Capra ◽  
Massimiliano Schwarz
Keyword(s):  
Slope Stability ◽  
Tree Species ◽  
Root Distribution ◽  
Mechanical Characteristics ◽  
Model Complexity ◽  
Small Scale ◽  
Soil System ◽  
Root Reinforcement ◽  
Essential Information ◽  
Pullout Tests

&lt;p&gt;The influence of vegetation on the hydro-geomorphological response is widely recognized, and root reinforcement mechanisms are an important component of slope stability models. The calculation of this essential information is very complex because of the multiple interactions in the root-soil system, but also because of several mechanical characteristics that influence the tension and compression behaviour of the root itself.&lt;/p&gt;&lt;p&gt;This contribution has two aims. The first one is to show parameters of root reinforcement effects of Robinia pseudoacacia (L.), a tree commonly used for the mitigation of rainfall-induced landslides at small scale. This species is very widespread because it is able to grow on marginal areas, such as abandoned hillside sites, or on infrastructures, such as road and railway scarps, but its characterization represents a gap in knowledge in the literature. Field pullout tests were performed to collect input data for the quantification of root reinforcement using the Root Bundle Model with Weibull survival function (RBMw, Schwarz et al, 2013). Recent studies have shown how the RBMw is a very efficient model for the evaluation of root reinforcement by considering the heterogeneity of both root mechanical characteristics and their distribution in the soil. However, due to the model complexity and the need for information difficult to obtain, other simpler but less accurate approaches, such as the Wu model, have been preferred.&amp;#160;&lt;/p&gt;&lt;p&gt;For this reason, the second aim of the work is to present a new tool written in C++, and called RBM++, easy to use that enables anyone, from Universities to private companies, to quantify the effect of roots on slope stability. RBM++ allows the calculation of root reinforcement using two different methods: the first one by entering own data of the mechanical parameters of the roots, estimated beforehand with pullout tests in the field, and the root distribution in the soil; the second one by selecting the tree species and the data related to the spatial root distribution. For the first method, it is necessary to use a pullout machine to obtain the data. Because this instrument is not commonly available the model has the option to use default parameters for nine tree species based on values found in the literature.&amp;#160;&lt;/p&gt;&lt;p&gt;Output from RBM++ comes in tabular format and with a plot that shows, via the graphical user interface, the spatial distribution of forces as a function of the distance from the tree trunk and size of the tree.&amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;&lt;p&gt;RBM++ makes it easier to share and exchange knowledge related to root reinforcement. Therefore, it will allow the realization of a database containing standard data on root mechanical behavior of tree species commonly used for shallow landslide mitigation.&lt;/p&gt;

scholarly journals Contribution of Tea Root Reinforcement to Soil Shear Strength on Slope Stability

2018 ◽  
Vol 4 (1) ◽  
pp. 13
Author(s):  
Mukhsin Abubakar
Keyword(s):  
Shear Strength ◽  
Slope Stability ◽  
Tensile Stress ◽  
Soil Condition ◽  
Soil Mass ◽  
Root Diameter ◽  
Root Reinforcement ◽  
Root Branching ◽  
Soil Shear Strength ◽  
Diameter Differentiation

Roots played important role in the process of stabilizing the soil mass. The geo-mechanical and soil-hydrological aspects on the slope are determined by, one of it, the root reinforcement. The role of root branching series with diameter differentiation is greatly determining its tensile stress. The tensile stress from the interaction between the root and the soil, could it contribute to increasing the shear strength of the slope stability. The purpose of this research was to identify the tensile stress on root branching series that interacted with the soil and created additional cohesion as a shear strength contribution to the slope stability. Testing on the root pulling force was conducted on slope prototype with angle 30o to 40o and has been planted with tea vegetation. A tripod that was completed with strain gauge as the recording instrument was used. Testing was conducted on two and three root branching, also on each unit by observing the diameter. This testing method was done in saturated soil condition. The tensile stress result showed that increasing diameter of the tea root, an increase was noticed, and also result in the equation of TFr = 0.089e0.516d. Root diameter increase on two and three root branching to one unit of tea vegetation showed that the stress increase was significant. When observed, in the root diameter differentiation of 4 mm to 6 mm, the stress on two and three root branching and one unit of tea vegetation were respectively 5.94%, 12.30%, and 35.42%. The contribution of additional cohesion caused by root-soil interaction to soil shear strength apparently could increase slope stability.

scholarly journals Tree-root control of shallow landslides

2017 ◽  
Vol 5 (3) ◽  
pp. 451-477 ◽  
Author(s):  
Denis Cohen ◽  
Massimiliano Schwarz
Keyword(s):  
Slope Stability ◽  
Traditional Approach ◽  
Shallow Landslide ◽  
Shallow Landslides ◽  
Tree Roots ◽  
Root Reinforcement ◽  
Apparent Cohesion ◽  
Root Strength ◽  
Weak Zones ◽  
Landslide Triggering

Abstract. Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models usually include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the self-organized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. The variation in root stiffness with diameter can, in some cases, invert this relationship. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of this force is comparable to the slope-perpendicular tensile force. In this case, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, a crack parallel to the slope forms near the top of the hillslope. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, intermediate-sized roots (5 to 20 mm in diameter) appear to contribute most to root reinforcement. Our results show more complex behaviors than can be obtained with the traditional slope-uniform, apparent-cohesion approach. A full understanding of the mechanisms of shallow landslide triggering requires a complete re-evaluation of this traditional approach that cannot predict where and how forces are mobilized and distributed in roots and soils, and how these control shallow landslides shape, size, location, and timing.

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