Root Reinforcement Research Articles

Biotechnical Characteristics of Root Systems of Typical Mediterranean Species

Vegetation can significantly contribute to stabilise sloping terrain by adding cohesion to soil: this reinforcement depends on the morphological characteristics of the root systems and the tensile strength of single roots. The paper presents the results of research carried out in order to evaluate the biotechnical characteristics of the root system of three typical Mediterranean plant species which can affect slope stability. The species considered in the present study are Lygeum spartum L. (a perennial herbaceous monocotyledonous), Atriplex halimus L. and Pistacia lentiscus L. (two dicotyledonous shrub species). The plant specimens were collected in the Basilicata region (Southern Italy) by in situ excavation to obtain the whole root systems. Single root specimens for each species were sampled and tested for tensile strength measurement, and the complete root systems were analysed to evaluate the root density distribution with depth in terms of Root Area Ratio. The resulting data have been used to calculate the reinforcing effect in terms of increased shear strength of the soil using the model of Wu (1976, Investigation of landslides on Prince of Wales Island. Geotech. Eng. Rep. 5 Civil Eng. Dep. Ohio State Univ. Columbus, Ohio, USA) and Waldron (1977, Soil Sci. Soc. Am. J. 41(3), 843–849), a simple and widespread model based on the reinforced earth theory. The results show that root reinforcement exerted by L. spartum is stronger than the reinforcement exerted by P. lentiscus and A. halimus in the upper layers of the soil, while P. lentiscus presents higher reinforcement values in deeper horizons. A. halimus presents lower values than either of the other species studied.

Root Strength and Root Area Ratio of Forest Species in Lombardy (Northern Italy)

Forest vegetation is known to increase hillslope stability by reinforcing soil shear resistance and by influencing hydrologic conditions of soil. Although the importance of plant root systems for hillslope stability has received considerable attention in recent years, the quantification of such an effect needs more investigation. In this paper, we present a synthesis of the data gathered in the last 5 years for some species in different locations of the Alps and Prealps of Lombardy (Northern Italy) with the aim to increase our knowledge on root tensile strength and on Root Area Ratio distribution within the soil. Concerning root tensile strength we developed tensile strength–diameter relationships for eight species: green alder (Alnus viridis(Chaix) D.C.), beech (Fagus sylvatica L.), red willow (Salix purpurea L.), goat willow (Salix caprea L.), hazel (Corylus avellana L.), European ash (Fraxinus excelsior L.), Norway spruce (Picea abies (L.) Karst.) and European larch (Larix decidua Mill.). Results show a great variability among the different species and also for the same species. In general, however, root strength (in terms of tension) tends to decrease with diameter according to a power law, as observed by other Authors. Comparing the power law fitting curves for the considered species, it can be observed that they fall in a relatively narrow band, with the exception of hazel, which appears the most resistant. Concerning the evaluation of root distribution within the soil we estimated the Root Area Ratio (the ratio between the area occupied by roots in a unit area of soil) according to its depth for five species (beech, Norway spruce, European larch, mixed hazel and ash) in three locations of Lombardy. Results show that there is a great variability of root density for the same species well as for different points at the same locality. The general behaviour of root density, in any case, is to decrease with depth according to a gamma function for all the studied species. The results presented in this paper contribute to expanding the knowledge on root resistance behaviour and on root density distribution within the soil. The studied location have allowed the implementation of soil–root reinforcement models and the evaluation of the vegetation contribution to soil stability.

Root architecture and wind‐firmness of mature Pinus pinaster

This study aims to link three-dimensional coarse root architecture to tree stability in mature timber trees with an average of 1-m rooting depth. Undamaged and uprooted trees were sampled in a stand damaged by a storm. Root architecture was measured by three-dimensional (3-D) digitizing. The distribution of root volume by root type and in wind-oriented sectors was analysed. Mature Pinus pinaster root systems were organized in a rigid 'cage' composed of a taproot, the zone of rapid taper of horizontal surface roots and numerous sinkers and deep roots, imprisoning a large mass of soil and guyed by long horizontal surface roots. Key compartments for stability exhibited strong selective leeward or windward reinforcement. Uprooted trees showed a lower cage volume, a larger proportion of oblique and intermediate depth horizontal roots and less wind-oriented root reinforcement. Pinus pinaster stability on moderately deep soils is optimized through a typical rooting pattern and a considerable structural adaptation to the prevailing wind and soil profile.

Estimating the mechanical effects of riparian vegetation on stream bank stability using a fiber bundle model

Recent research has suggested that the roots of riparian vegetation dramatically increase the geomechanical stability (i.e., factor of safety) of stream banks. Past research has used a perpendicular root reinforcement model that assumes that all of the tensile strength of the roots is mobilized instantaneously at the moment of bank failure. In reality, as a soil‐root matrix shears, the roots contained within the soil have different tensile strengths and thus break progressively, with an associated redistribution of stress as each root breaks. This mode of progressive failure is well described by fiber bundle models in material science. In this paper, we apply a fiber bundle approach to tensile strength data collected from 12 riparian species and compare the root reinforcement estimates against direct shear tests with root‐permeated and non‐root‐permeated samples. The results were then input to a stream bank stability model to assess the impact of the differences between the root models on stream bank factor of safety values. The new fiber bundle model, RipRoot, provided more accurate estimates of root reinforcement through its inclusion of progressive root breaking during mass failure of a stream bank. In cases where bank driving forces were great enough to break all of the roots, the perpendicular root model overestimated root reinforcement by up to 50%, with overestimation increasing an order of magnitude in model runs where stream bank driving forces did not exceed root strength. For the highest bank modeled (3 m) the difference in factor of safety values between runs with the two models varied from 0.13 to 2.39 depending on the riparian species considered. Thus recent work has almost certainly overestimated the effect of vegetation roots on mass stability of stream banks.

Structural resistance in immature teeth using root reinforcements in vitro

The purpose of this study was to evaluate in vitro the efficacy of root reinforcements by light-cured composite resin or zirconium fiber post in simulated immature non-vital teeth. Fifty-six bovine incisors teeth were used for this study. The crown of each tooth was removed in the medium third to obtain a standard length of 30 mm. The specimens were divided into four groups (n = 14): G1) the root canals were instrumented and enlarged to simulate immature non-vital teeth and were reinforced with a light-cured composite resin using a translucent curing post (Luminex system); (G2) the specimens were instrumented, enlarged and they received root reinforcement with zirconium fiber post; G3 (positive control): they received similar treatment to the G1 and G2 groups, but did not receive root reinforcement; G4 (negative control): the roots were not weakened and did not receive reinforcement. Every tooth was submitted to compressive force using an Instron testing machine with an angle of 45 degrees at a speed of 1 mm min(-1) until the fracture. The results showed a markedly increased resistance to fracture in the G1 and G2 (122.38 and 122.08 kg f, respectively). Among the results of G1 and G2 there was not any significant difference (P > 0.05) but they were significantly different from the control groups (P < 0.05). The conclusion is that the use of root reinforcements with zirconium fiber post or composite resin can increase significantly the structural resistance of the weakened teeth, decreasing the risk of the fracture.

Effect of seed source and nursery culture on paper birch ( Betula papyrifera) uprooting resistance and field performance

Little is known about the effect of seed source and nursery culture on the growth and performance of artificially regenerated paper birch planted in the field. In the summer of 2000, trees were vertically uprooted in Prince George, BC using a tripod and winch device to determine if seed source and nursery culture significantly affected the root strength of 5-year-old paper birch. Trees from a seed source in the Skeena region had the greatest uprooting resistance, and the most root biomass, but the least root strength compared to the other three seed sources tested. The Skeena trees may be exhibiting an adaptive strategy which provides maximum root reinforcement across a wide range of environments. Uprooting resistance was similar for the 415D stocktypes grown at Red Rock and Kalamalka nurseries. However, trees grown in 515A styroblock at Kalamalka had the least uprooting resistance and root biomass of all treatments. In addition, the relationship between uprooting resistance and ground line diameter was different between nurseries. The results of this study suggest that regardless of height and diameter leaving the nursery, seed source root resistance and growth continued to be impacted by nursery culture 5 years after planting.

Slope stability of forested slopes considering effect of tree root and steel bar reinforcement

A tree root crossing through upper soil layer into bedrock increases shear strength of soil and renders the slope more stable. The effect of root reinforcement on soil strength has been well researched through the mechanistic and empirical studies, but yet few studies have examined how tree roots in combination with steel bar influence slope stability. Further, most of previous research lacked consideration of effect of slope displacement on the reinforcement of tree roots and steel bars.By using actual distribution of tree root, an analysis of slope stability considering tree root reinforcement as a function of groundwater level and slope displacement will be proposed. Larger displacement of slope results in greater reinforcement of tree root. The resisting force and displacemen increase until the slope becomes stable. For some reasons (external load, more rainfall. etc), if the slope became unstable again, the process of landslide repeats until Fs=1. Tree root functions like reinforcement material and improves factor of safety of forested slope, Fs≥1. However, target factor of safety (also called design factor of safety Fds) of a forested slope must be equal to or higher than a standard value (such as Fds= 1.2 in this paper). Magnitude of Fds depends on the importance of slope. Thus, we need extra reinforcement even if the slope has tree root reinforcement. There are many methods to reinforce slope. In this paper, steel bar is chosen for two reasons: 1) steel bar has the same behavior as a root in a landslide; 2) steel bar is one of very few methods that can sustain the vegetation on slope. By applying model of inclined root proposed by Nghiem et al.(2001, 2003), a design method is presented for root fibers reinforcing slope in combination with steel bars.

Discussion of "Slope stability thresholds for vegetated hillslopes: a composite model"

Wu 1062 The authors have presented a method to estimate the threshold rainfall that would trigger failures on slopes with various amounts of root reinforcement. The method is used for land management in New Zealand. In this discussion, the writer wishes to point out that the method is based on several assumptions that need attention before the method can be considered generally applicable.

Paper birch and lodgepole pine root reinforcement in coarse-, medium-, and fine-textured soils

The increased soil cohesion or reinforcement provided by roots varies among plant species and soil types. This study compared the contribution of paper birch (Betula papyrifera Marsh.) and lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) roots to soil shear resistance in two controlled environment experiments. Roots of paper birch and lodgepole pine trees contributed to a significant increase in soil shear resistance, regardless of soil type. At a shear depth of 0.20 to 0.44 m, paper birch contributed greater reinforcement than lodgepole pine. Both birch and pine provided the most root reinforcement in coarse-textured soil and the least reinforcement in medium-textured silt soil. Soil texture, porosity, and shear strength may have affected root branching of the two species, which in turn may have affected root reinforcement. At less than 1 year of age, paper birch trees planted as plugs can substantially increase soil shear strength compared with lodgepole pine in all soil types.

Assessment of landslide hazard under combined loading

A method for assessing landslide hazard under combined loading is described. The loads are considered as pulses that occur randomly in time. The method accounts for the rate of occurrence and the duration of the loads and calculates the rate of coincidence of two or more loads. This is used to calculate the failure probability, which is equal to the probability that the load combination will exceed a threshold value during a given time period. The method was applied to a site in the Cascade Mountains of Washington. The loads considered include those as a result of gravity, pore pressure from infiltration of rainfall plus snowmelt, loss of root reinforcement through fire or logging, and earthquakes. The example demonstrates a rational approach that accounts for the properties of the loads and the different loading conditions that may be expected.Key words: earthquake, failure probability, landslide hazard, load coincidence, load combination, pore pressure, root reinforcement.

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The purpose of this study was to perform a finite element analysis to determine whether adhesive reconstruction is able to restore the original biomechanical behaviour of weakened roots, in terms of fracture resistance, when compared with post/crown-restored teeth with intact roots.A three-dimensional model of a maxillary central incisor was created. The model simulated an endodontically treated tooth restored with a glass-fibre post, a composite-resin core and a metal crown (Model 1). Based on Model 1, a new volume was created in the root cervical third that represented the area where the dentine structure was lost, resulting in a structurally damaged root (Model 2). A 100 N load was applied to the palatal surface at 130° from the long axis of the tooth. After processing (Ansys® 10.0 – Canonsburg, PA, USA), the principal normal stress data were analyzed (S1, tensile; S3, compressive).The models demonstrated a similar S1 distribution concentrated in the lingual cervical region but different S1 levels (Model 1: 28.7 MPa; Model 2: 35.3 MPa). The S3 distribution indicated differences in behaviour between the models (Model 1: −18 to −27 MPa along the buccal root surface; Model 2: −25 to −32 MPa on the post buccal surface and along the buccal root wall).Although the stress distribution within the root walls remained below the ultimate stress limit of the root dentine, the adhesive reconstruction of the weakened roots did not recover the load resistance of structurally intact roots.The decision of when to prosthetically rehabilitate weakened roots with cervical dentine structural tissue loss is a challenge for clinicians. A ‘monoblock’ adhesive reconstruction has been proposed for root reinforcement. During treatment planning, the possibility of restoring the mechanical resistance of the root must be evaluated if successful long-term results are to be achieved.

Shallow landsliding, root reinforcement, and the spatial distribution of trees in the Oregon Coast Range

The influence of root reinforcement on shallow landsliding has been well established through mechanistic and empirical studies, yet few studies have examined how local vegetative patterns influence slope stability. Because root networks spread outward from trees, the species, size, and spacing of trees should influence the spatial distribution of root strength. We documented the distribution and characteristics of trees adjacent to 32 shallow landslides that occurred during 1996 in the Oregon Coast Range. Although broadly classified as a conifer-dominated forest, we observed sparse coniferous and abundant hardwood trees near landslide scars in an industrial forest (Mapleton) that experienced widespread burning in the 19th century. In industrial forests that were burned, selectively harvested, and not replanted (Elliott State Forest), swordfern was ubiquitous near landslides, and we observed similar numbers of live conifer and hardwood trees proximal to landslide scarps. We demonstrate that root strength quantified in landslide scarps and soil pits correlates with a geometry-based index of root network contribution derived from mapping the size, species, condition, and spacing of local trees, indicating that root strength can be predicted by mapping the distribution and characteristics of trees on potentially unstable slopes. In our study sites, landslides tend to occur in areas of reduced root strength, suggesting that to make site-specific predictions of landslide occurrence slope stability analyses must account for the diversity and distribution of vegetation in potentially unstable terrain.Key words: slope stability, vegetation, root strength, shallow landslide, debris flow, Oregon Coast Range.

Analysis of root reinforcement at slip surface.

In this paper. a theoretical model is proposed to investigate the behavior of tree roots subjected to mass movement and to determine the reinforcement capacity of tree roots at slip surface of landslide. Tree roots function as a type of reinforcement material to minimize landslide. By modelling a root system as a cluster of root fibers inserted through the unstable soil to the bedrock, the increase in the shear resistance of soil can be reliably estimated. Properties and distribution of the roots are taken from a number of previous field experiments. Roots used in the model are Japanese cedar (Criptomeria japonica) roots, the most popular species in Japan. With the inclined roots classified by inclinations and diameters, the relationship between reinforcement capacity of root fibers and horizontal displacements is analyzed under two main conditions: ultimate stress and pullout resistance. The computed results of the tree root model are used in the prediction of root reinforcement at slip surface of a previous soil-shear test. There is, in general, a reasonable agreement between predicted results and experimental data.

The Effects of Riparian Vegetation on Bank Stability

In northern Mississippi, roots in riparian zones were studied in an attempt to quantify the effects of root reinforcement of the soil matrix. The roots of trees can be treated as elastic-reinforced elements, and a function of the tensile strength of the roots can be added directly to the Mohr-Coulomb equation for failure criteria. Estimating root reinforcement and root-soil matrix interactions allows for the determination of whether bank vegetation is beneficial or detrimental. The research was conducted at the Goodwin Creek Experimental Watershed, located near Batesville, MS. This investigation quantifies root tensile strength of the sweet gum ( Liquidamar syraciflua ) in a cohesive, fine-grained, primarily loess-derived fluvial material. During the field research, trenches were excavated to gain access to the roots being studied. These trenches allowed mapping of the roots, as well as direct tensile testing of the roots. Increased tensile strength due to root reinforcement was found to be between 0.0 and 245 kPa, depending on depth. For a given depth of 40 cm, the increased tension due to root reinforcement averaged 148 kPa, depending on lateral distance from tree. A modified root reinforcement model was developed to explain the root-soil interaction observed at the research site. Itasca's Fast Lagrangian Analysis of Continua model was employed in determining the role of root reinforcement. The modeling results showed a contrast between root-reinforced and unreinforced soil. When no root reinforcement existed, the slope failed marginally. When simulated root reinforcement of 20 kPa was applied, the slope was shown to be completely stable.

Quantifying the mechanical and hydrologic effects of riparian vegetation on streambank stability

AbstractRiparian vegetation strips are widely used by river managers to increase streambank stability, among other purposes. However, though the effects of vegetation on bank stability are widely discussed they are rarely quantified, and generally underemphasize the importance of hydrologic processes, some of which may be detrimental. This paper presents results from an experiment in which the hydrologic and mechanical effects of four riparian tree species and two erosion‐control grasses were quantified in relation to bank stability. Geotechnical and pore‐water pressure data from streambank plots under three riparian covers (mature trees, clump grasses and bare/cropped turf grass) were used to drive the ARS bank stability model, and the resulting factor of safety (Fs) was broken down into its constituent parts to assess the contribution (beneficial or detrimental) of individual hydrologic and mechanical effects (soil moisture modification, root reinforcement and surcharge). Tree roots were found to increase soil strength by 2–8 kPa depending on species, while grass roots contributed 6–18 kPa. Slope stability analysis based on data collected during bank failures in spring 2000 (following a very dry antecedent period) shows that the mechanical effects of the tree cover increased Fs by 32 per cent, while the hydrologic effects increased Fs by 71 per cent. For grasses the figures were 70 per cent for mechanical effects and a reduction of Fs by 10 per cent for the hydrologic effects. However, analysis based on bank failures in spring 2001 (following a wetter than average antecedent period) showed the mechanical effects of the tree cover to increase Fs by 46 per cent, while hydrologic effects added 29 per cent. For grasses the figures were 49 per cent and −15 per cent respectively. During several periods in spring 2001 the hydrologic effects of the tree cover reduced bank stability, though this was always offset by the stabilizing mechanical effects. The results demonstrate the importance of hydrologic processes in controlling streambank stability, and highlight the need to select riparian vegetation based on hydrologic as well as mechanical and ecological criteria. Published in 2002 by John Wiley &amp; Sons, Ltd.

Landslides on coastal sage-scrub and grassland hillslopes in a severe El Niño winter: The effects of vegetation conversion on sediment delivery

During the 1997-1998 El Nino, record rainfall triggered.150 shallow landslides within a 9.5 km2 area near Santa Barbara, Cal- ifornia. They were studied to analyze the sediment delivery to val- ley floors from landslides in coastal sage scrub and converted grasslands. The conversion of coastal sage to grasslands, primarily to provide pasturage for cattle, is common in the region, and the landscape's response may affect water quality, reservoir infilling, and debris flow hazards. We explore the relationship between lateral- root reinforcement and landslide volume by developing a slope- stability analysis that incorporates root cohesion along the sides of the failure. The stability analysis correctly predicts an inverse re- lationship between landslide volume and hillslope angle in the sage. The volumes of failures in the grasslands do not vary systemati- cally with slope and are generally smaller than those in the sage. From aerial-photograph analysis and field mapping, we find that there are 22.9 failures per square kilometer in the grasslands com- pared to 13.2 failures per square kilometer in the sage. Despite the lower failure density in the coastal sage, greater failure volumes and longer transport distances delivered more sediment to valley floors, with a specific volumetric flux of 2.8 3 10 -2 m 3 ·m -1 for this El Nino compared to 1.73 10 -2 m 3 ·m -1 in the grasslands. We con- clude that the conversion from vegetation with stronger and deeper roots (coastal sage) to vegetation with weaker and shallower roots (grass) has caused a pulse of increased landsliding in the grasslands because the soils are currently too thick for the prevailing root reinforcement. We suggest that, over time, soils in the grassland hollows will become thinner as the evacuation by landslides is re- peated until the landsliding rate declines to balance the soil sup- plied from local colluvium production and diffusive processes upslope.

The distribution and strength of riparian tree roots in relation to riverbank reinforcement

AbstractThe main influences of plants on the mass stability of riverbanks are those that affect the strength of bank sediments. Plants enhance bank strength by reducing pore‐water pressures and by directly reinforcing bank material with their roots. In this paper we do not consider bank hydrology but focus on quantifying increases in sediment strength due to root reinforcement. Root reinforcement is a function of root strength, interface friction between the roots and the soil, and the distribution of roots within the soil. Field and laboratory studies of Australian riparian trees, river red gum (Eucalyptus camaldulensis) and swamp paperbark (Melaleuca ericifolia), indicate that bank reinforcement, due to the roots of these species, decreases exponentially with depth below the soil surface and distance away from the trees. Differences in the spatial distribution of root reinforcement are illustrated by a comparison of the apparent cohesion due to roots (cr) with the effective cohesion of the saturated bank material (15 kPa). Directly below the river red gum, root reinforcement is equal to effective cohesion at 1·7 m depth. At the dripline (17 m from the trunk), root reinforcement is equal to material strength at 0·4 m depth. For the swamp paperbark, cr=15 kPa at 1·1 m depth beneath surface, at the trunks, and at 0·4 m depth at the dripline (2·5 m from the trunk). A description of the spatial distribution of root reinforcement is important in the riverbank context. We find that interspecies differences in the strength of living roots have less significance for bank reinforcement than interspecies differences in root distribution. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Effects of soil suction on root reinforcement in unsaturated forest soil

Effects of soil suction on root reinforcement in unsaturated forest soil

Variable polarity plasma arc welding of 6·35 mm aluminium alloys: parameter development and preliminary analysis

The application of the variable polarity plasma arc welding (VPPAW) process to two medium to high strength 6·35 mm thickness aluminium alloys is described. Automated computer controlled equipment was used to produce single pass, full penetration keyhole welds of even bead width. The paper covers the development and optimisation of the welding parameters and different material preparation procedures, providing macrographs, electrical transient traces, hardness profiles, and tensile results from some of the welds made. Repeatable procedures were obtained more easily by welding in the vertical up position, using the plasma gas flowrate in conjunction with the welding current to generate the desired bead profile. Autogenous welded joints were found to provide adequate root reinforcement with a slight degree of undercutting at the top bead. Example skimmed and as welded tensile tests were carried out on 2024 alloy, resulting in a typical overall ultimate tensile welded performance of 66% of the parent strength.

Variable polarity plasma arc welding of 6·35 mm aluminium alloys: parameter development and preliminary analysis

The application of the variable polarity plasma arc welding (VPPAW) process to two medium to high strength 6·35 mm thickness aluminium alloys is described. Automated computer controlled equipment was used to produce single pass, full penetration keyhole welds of even bead width. The paper covers the development and optimisation of the welding parameters and different material preparation procedures, providing macrographs, electrical transient traces, hardness profiles, and tensile results from some of the welds made. Repeatable procedures were obtained more easily by welding in the vertical up position, using the plasma gas flowrate in conjunction with the welding current to generate the desired bead profile. Autogenous welded joints were found to provide adequate root reinforcement with a slight degree of undercutting at the top bead. Example skimmed and as welded tensile tests were carried out on 2024 alloy, resulting in a typical overall ultimate tensile welded performance of 66% of the parent strength.