Root Reinforcement Research Articles

The Affecting Factors of Soil-Reinforcement by Plant Roots

Now, with the large-scale of various projects constructed, a lot of the original vegetation were destroyed and formed a large area of bare slope. The existence of slopes increased the occurrent intensity of soil erosion, landslides and debris flow, and also caused local ecological disasters of the deterioration of the microclimate and the destruction of the biological chain. Based on this situation, this article discussed the reinforced soil reinforcement of shallow fine roots and deep rough roots, and generalized comprehensively the root factors on the impact of the reinforced soil, and explored the lack of research and development trends of vegetation slope protection.

Mechanism of autograft insufficiency after the Ross operation in children

It is unclear how autografts grow and dilate after the Ross operation in children. We analysed autograft growth and dilatation in children who underwent the Ross operation and examined the relationship of these factors to autograft failure. From our institutional database, we retrospectively identified 33 children who underwent the Ross operation without aortic root reinforcement (mean age 9.9 years) and had normal body measurements and echocardiographic data throughout follow-up. Autograft insufficiency developed in 10 patients 5.1 years after the Ross operation. The average Z score at the development of autograft insufficiency was -0.1 (range from -2.0 to 6.1). The proportions of patients who remained free of autograft insufficiency at 5 and 10 years were 87.2% and 55.7%, respectively. A consistent trend in the time course of Z score was not found in any age group studied. Autograft growth and dilation after the Ross operation varied widely among patients, and the incidence of autograft insufficiency was independent of annulus size.

Mechanical interactions between neighbouring roots during pullout tests

The quantification of root reinforcement function is important for landscape managers and engineers. The estimation of root mechanical reinforcement is often based on models that do not consider the potential interaction between neighbouring roots. Root-soil mechanical interactions related to the root spacing and bundle geometry remain unclear including potential effects on the reliability of the current models. The objective of this study is to quantify the mechanical interactions among neighbouring roots or roots networks using modelling approaches and pullout laboratory experiments. Based on simple geometrical characterization of individual root geometry, we calculated dissipation patterns of frictional root-soil interfacial stresses in radial and longitudinal directions. Considering simple superposition of shear stresses within the soil matrix, we quantified characteristic root densities at which the radial mechanical interactions influence global pullout behaviour of the root bundle both for branched and unbranched roots. Laboratory pullout tests on root bundles were carried out at root spacings of 15, 35 and 105 mm. In addition, we tested effects of non-parallel (crossing) root bundle geometry. We found no significant statistical differences in root pullout force for the different root spacing in parallel alignment of roots. Branches increase pullout force by 1.5 times. Moreover, the mean displacement at the pullout peak-force was 7.2 % of length for unbranched roots and about 4.1 % of length for branched roots. The model shows its potential comparing it with empirical results concerning the holes leaved by roots, according with the branch pattern. The study quantifies the influence of root spacing and arrangement geometry within a root bundle on its mechanical behaviour. The assumption of “non-interacting” neighbouring roots in root reinforcement methods is no longer valid for root spacing less than 15 mm and root reinforcement methods. Moreover crossing roots shown a statistical difference. This information is important for improved understanding root reinforcement mechanisms in steep hill slope and the interplay between anchoring /failure and root bundle pullout vs root breakage.

Mechanical Characteristics of Peanut Root System and its Tribological Properties against Soil

Peanut root of crop lands in Menglianggu watershed in the upper reaches of Yi River were classified into different diameter classes by root diameter. The results show that (1) the relationship between force of pullout or breaking and root diameter is approximately linearity, and more significant linear for the latter; (2) Laboratory tests confirm the presence of a threshold or range of root diameter. When the diameter within the range (1.80-3.01mm), both root breaking and pullout occurred; when the diameter above 3.01mm, all roots broke under applied stress. While below 1.80mm, only roots were pulled out under applied stress. Root-soil resistance characteristic and root reinforcement effect were analyzed for different root classes: (3) pull out force of root-soil resistance is stronger than that of single root of the same root classes with the range from 6.03% to 39.39%.

Impact of floods on the statistical distribution of riverbed vegetation

Investigating the colonization of river bars by pioneer vegetation, we discuss how the balance between uprooting by flooding events and reinforcement of plant roots determines the ability for vegetation to colonize the riverbed. In order to access the competition between growth and uprooting, we work in a regime where the arrival time of flooding events is comparable with the timescales associated with vegetation, i.e., plant germination and development rates. We present new results for a flume experiment using converging channel walls and draw contrasts with previously published results for a simple channel with parallel sides. This comparison highlights the role of varying local stream power in these processes. We collected the statistics of vegetation root length, number of roots and stem height for both riverbed and uprooted vegetation and show using a stochastic approach how the statistics for vegetation surviving in the riverbed after a flood result from both the distribution of riverbed biomass before the flood and the distribution of biomass that is uprooted by the flood. Finally, we compare our laboratory results with data obtained in a field experiment to show the similarities in the uprooting processes at both scales.

Reoperations on the pulmonary autograft and pulmonary homograft after the Ross procedure: An update on the German Dutch Ross Registry

Reinterventions after the Ross procedure are a concern for patients and treating physicians. The scope of the present report was to provide an update on the reinterventions observed in the large patient population of the German-Dutch Ross Registry. From 1988 to 2011, 2023 patients (age, 39.05 ± 16.5 years; male patients, 1502; adults, 1642) underwent a Ross procedure in 13 centers. The mean follow-up was 7.1 ± 4.6 years (range, 0-22 years; 13,168 patient-years). In the adult population, 120 autograft reinterventions in 113 patients (1.03%/patient-year) and 76 homograft reinterventions in 67 patients (0.65%/patient-year) and, in the pediatric population, 14 autograft reinterventions in 13 patients (0.91%/patient-year) and 42 homograft reinterventions in 31 patients (2.72%/patient-year) were observed. Of the autograft and homograft reinterventions, 17.9% and 21.2% were performed because of endocarditis, respectively. The subcoronary technique in the adult population resulted in significantly superior autograft durability (freedom from autograft reintervention: 97% at 10 years and 91% at 12 years; P<.001). The root replacement technique without root reinforcement (hazard ratio, 2.4; 95% confidence interval, 1.4-4.1) and the presence of pure aortic insufficiency preoperatively (hazard ratio, 2.3; 95% confidence interval, 1.5-3.5) were statistically significant predictors for a shorter time to reoperation. The center volume had a significant influence on the long-term results. The freedom from homograft reoperation for the adults and pediatric population was 97% and 87% at 5 years and 93% and 79% at 12 years, respectively (P<.001), with younger recipient and donor age being significant predictors of a shorter time to homograft reoperation. The autograft principle remains a valid option for young patients requiring aortic valve replacement. The risk of reoperation depends largely on the surgical technique used and the preoperative hemodynamics. Center experience and expertise also influence the long-term results. Adequate endocarditis prophylaxis might further reduce the need for reoperation.

Modelling root demography in heterogeneous mountain forests and applications for slope stability analysis

Plant roots provide mechanical cohesion (c r ) to soil on slopes which are prone to shallow landslides. c r varies in heterogeneous natural forests due to the spatial, inter- and intra-annual dynamics of root demography. Characterizing root initiation density and mortality, as well as how root growth is influenced by abiotic and biotic factors is essential for exploring a root system’s capacity to reinforce soil. In this study, root demography data were monitored using field rhizotrons during 1.5 years in two naturally regenerated mixed forests in the French Alps. These forests are composed of trees growing in groups (tree islands) with large gaps between the islands. Three categories of driving variables were measured: (i) spatial factors: altitude (1,400 m, 1,700 m), ecological patch (gap, tree island), soil depth (0.0–1.0 m divided into five layers of 0.2 m); (ii) temporal factors: month (12 months from March 2010 to February 2011), winter (winter of 2009–2010 and 2010–2011); (iii) biological factors: root diameter classes (]0, 1] mm, ]1, 2] mm, ]2, 5] mm (according to the international standard ISO 31–11, ]x, y] denotes a left half-open interval from x (excluded) to y (included)). Two types of two-part models, a Hurdle model (H) and a Zero-inflated model (ZI) were used to fit root data with a high zero population, i.e. if root initiation or mortality was zero during a given time period, or if roots were not present at all points throughout a soil profile. Root initiation quantity decreased with increasing soil depth, as well as being lower in tree islands. Both soil depth and ecological patch interacted strongly with altitude. Root dynamics were significantly less active with a lower net production and c r increment in winter and spring than in summer and autumn. Roots which were ]1, 2] mm in diameter contributed the most to c r compared to other diameter classes, as they had a high production but a low mortality. With regard to model selection, both H and ZI demonstrated similar outcomes and underestimated extreme values of root demography data. All factors contributed towards explaining the variability of root demography and c r . We suggest taking into consideration the seasonality of root dynamics when studying root reinforcement.

Spatial characterization of root reinforcement at stand scale: Theory and case study

We propose a new upscaling approach for quantify root reinforcement at the stand scale using the spatially explicit root bundle model (RBM) for describing pullout force-displacement behavior coupled with a model for lateral root distribution. The root distribution model was calibrated using data of two excavated soil profiles, and validated with measurements of root distribution along the scarp of an artificially rainfall-triggered landslide in a vegetated hillslope above the Rhine river in northern Switzerland. Results show that the model overestimates small root density (1–3mm diameter), leading to an error in estimated maximum root reinforcement of about 28%. For comparison, the most commonly used model of Wu overpredicts root reinforcement by a factor of 3. The spatial variability of estimated maximum root reinforcement within the forest stand is high, ranging from 0 to 20kPa. Most soil reinforcement by roots occurs close to the tree stem or in zones where root systems overlap. The new approach provides a detailed description of maximum root reinforcement on a slope, an essential element for the prediction of shallow landslides and the management of protection forests.

Plant root traits affecting the resistance of soils to concentrated flow erosion

ABSTRACTThe effect of plant species on erosion processes may be decisive for long‐term soil protection in degraded ecosystems. The identification of functional effect traits that predict species ability for erosion control would be of great interest for ecological restoration purposes. Flume experiments were carried out to investigate the effect of the root systems of three species having contrasted ecological requirements from eroded marly lands of the French Southern Alps [i.e. Robinia pseudo acacia (tree), Pinus nigra austriaca (tree) and Achnatherum calamagrostis (grass)], on concentrated flow erosion rates. Ten functional traits, describing plant morphological and biomechanical features, were measured on each tested sample. Analyses were performed to identify traits that determine plant root effects on erosion control. Erosion rates were lowest for samples of Robinia pseudo acacia, intermediate in Achnatherum calamagrostis and highest in Pinus nigra austriaca. The three species also differed strongly in their traits. Principal components analysis showed that the erosion‐reducing potential of plant species was negatively correlated to root diameter and positively correlated to the percentage of fine roots. The results highlighted the role of small flexible roots in root reinforcement processes, and suggested the importance of high root surface and higher tensile strength for soil stabilization. By combining flume experiment to plant functional traits measurements, we identified root system features influencing plant species performance for soil protection against concentrated flow erosion. Plant functional traits related to species efficiency for erosion control represent useful tools to improve the diagnosis of land vulnerability to erosion, plant community resistance and the prediction of ecosystem functioning after ecological restoration. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Effects of gauge length and strain rate on the tensile strength of tree roots

Root tensile strength plays an important role in soil stabilization and fixation. Testing and separating the different factors that affect root tensile strength are important. In the present study, the effects of four factors, namely, gauge length, strain rate, species, and root diameter, on root tensile strength were studied. Uniaxial tensile tests were conducted to acquire the root tensile strength of five tree species commonly growing in the mountains of northern China, namely, Chinese pine (Pinus tabulaeformis Carr.), Larch (Larix principis-rupprechtii Mayr.), White birch (Betula platyphylla Suk.), Mongolian oak (Quercus mongolicus Fisch.), and Elm (Ulmus pumila L.). Based on the results, Elm and White birch roots were the most resistant to tension, followed by Mongolian oak and Chinese pine roots. Larch roots were found to be the least resistant to tension. A power relationship was established between root diameter and root tensile strength. Based on linear regression analysis, gauge length was negatively correlated with root tensile strength. Tensile strength decreased with increasing gauge length. In addition, an unexpected variation of tensile strength was observed between two strain rates (10 and 400 mm min−1). The present study can serve as a basis for further studies on mechanical properties of root system and root reinforcement under different test circumstances, although this should be done with caution.

Numerical modelling of wave overtopping-induced erosion of grassed inner sea-dike slopes

Recent field wave overtopping experiments on grassed sea-dikes indicate that a moderate-quality grass cover can surprisingly resist severe overtopping rates. This high erosion-resistant capacity against wave overtopping of grass covers is owing to the root reinforcement of grass in the subsoil. Inspired by this finding, the present study makes first attempt to develop a numerical model of wave overtopping-induced erosion of the inner slope of grassed sea-dikes, considering the effect of the root reinforcement. The critical velocity for grass erosion is described as a function of the root cohesion and thus decreases with the erosion depth. This depth-dependent strength of grass allows for a better description of the nature of grass erosion, especially eligible for modelling erosion initiated from a naturally or artificially weak spot in a grass slope. Wave overtopping on grass slopes exhibits high turbulence with entrained air bubbles, for which the bed shear stress determined according to the conventional approach for ordinary open-channel flows is underestimated. To resolve this, it is assumed that the structure of wave overtopping resembles that in a bubbly turbulent wall jet, so that the bed shear stress can be determined in connection with the degree of flow turbulence. Model validation against the data from field overtopping experiments conducted in the Netherlands shows that main features of grass erosion on landward dike slopes are successfully simulated. Numerical experiments on various aspects of grass erosion are carried out which give some new insights into the nature of wave overtopping-induced grass erosion. Also, if the process of breach initiation of a grassed dike can be divided into subprocesses, erosion of the grass turf and erosion of the bare clay cover, an attempt is successfully made to roughly anticipate the breach initiation time of grassed sea-dikes composed of a sand core and a grassed clay cover.

Hydromechanical triggering of landslides: From progressive local failures to mass release

Water infiltrating during intense rainfall on steep slopes gradually weakens the wet soil mass, inducing localized failures that may initiate a cascade of load redistributions and successive failures propagating across a hillslope. The challenge of linking the progressive nature of local events culminating in an abrupt landslide is addressed by a new hydromechanical triggering model that links key hydrologic processes with threshold‐based mechanical interactions. A hillslope is represented as assembly of soil columns interconnected by frictional and tensile mechanical bonds represented as virtual bundles of fibers. Increasing water load exerted on mechanical bonds causes gradual failure of fibers until restraining forces are exceeded. Following failure at the soil‐bedrock interface, the load on a column is redistributed to its neighbors via intact mechanical (primarily tensile) bonds which, in turn, may also fail and transmit the load downslope as compressive stresses. When soil internal compressive strength is exceeded, a load‐bearing column may liquefy and initiate a landslide release that could propagate downslope or retrogressively upslope. The model reproduces observed power law frequency magnitude relationships of landslides with exponents ranging between −1.0 and −2.2 in agreement with landslide inventory data. We applied a criticality measure defined by Ramos (2011) to evaluate the specific influences of slope angle, soil texture, and root reinforcement on attainment of hillslope criticality in which a small local failure may trigger release of a large soil mass. The model provides new insights on the conditions giving rise to an abrupt transition from a seemingly stable hillslope to a catastrophic landslide.

Numerical analysis of the biomechanical behaviour of a weakened root after adhesive reconstruction and post-core rehabilitation

ObjectivesThe 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. MethodsA 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 100N 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). ResultsThe models demonstrated a similar S1 distribution concentrated in the lingual cervical region but different S1 levels (Model 1: 28.7MPa; Model 2: 35.3MPa). The S3 distribution indicated differences in behaviour between the models (Model 1: −18 to −27MPa along the buccal root surface; Model 2: −25 to −32MPa on the post buccal surface and along the buccal root wall). ConclusionsAlthough 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. Clinical significanceThe 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.

Effect of spatial variation of tree root characteristics on slope stability. A case study on Black Locust (Robinia pseudoacacia) and Arborvitae (Platycladus orientalis) stands on the Loess Plateau, China

Vegetation is widely used for controlling shallow landslides. The mechanisms by which roots increase apparent soil cohesion is well documented and many values of root additional cohesion are available in the literature for different plant species. However, less information is given about the spatial variation of soil reinforcement by roots at a slope scale and its influence on slope stability, in particular in forest areas. The goal of this paper is to describe the spatial variability of root additional cohesion on two monospecific 17-y-old stands of Robinia pseudoacacia and Platycladus orientalis grown on slopes in the semiarid Loess Plateau of China, and to analyze numerically the effect of this variability on slopes stability. For this purpose, vertical trenches were dug at different distance and directions around trees situated at three different slope locations, i.e. up-, mid- and down-slope. Grids with a 10×10 cm mesh were placed on vertical walls. Roots were counted within each grid cell and split according to their diameter class. Root area ratio (RAR) was estimated and compared among different positions around the trees and at three different locations along the slope. Roots tensile strength was determined with laboratory mechanical tests. RAR and root tensile strength were used as inputs in six different root reinforcement models to calculate root additional cohesion. A 2D finite element model of slope stability was developed and used to calculate the increase in factor of safety (FoS) due to root additional cohesion on rectilinear and terraced slopes. Results showed that both root tensile strength and Young's modulus of R. pseudoacacia was about two times higher than tensile strength of P. orientalis. RAR distribution had a strong relationship with local soil moisture content measured in July during the raining season, and was significantly different with regards to tree location on the slope. The six theoretical models used to estimate the root additional cohesion gave different vertical profiles of root reinforcement distribution according to the underlying hypothesis on how forces are transferred to the roots. Theoretical analyses of slope stability showed that terraced slopes were 20% more stable than rectilinear slopes, disregarding the differences in hydrological regimes between these two terrain morphologies. Numerical sensitivity analyses also showed that the FoS reached an asymptotic value when increasing root additional cohesion. Actual additional cohesions of the two studied sites corresponded to FoS that were already close to this asymptotic values. Consequently variations of these actual root cohesions would not much affect slope stability. However it was showed that more attention should be given to the reinforcement of the bottom part of the actual slopes, where roots have a larger positive impact on the FoS

Centrifuge modelling of soil slopes containing model plant roots

A series of centrifuge model tests were conducted to investigate the contribution of root reinforcement to slope stability. A compacted sandy clay slope, inclined at 45°, was reinforced with model roots. The model roots were varied in material, architecture, and numbers. They had stiffness values corresponding to upper and lower values found for plant roots. The architecture included taproots and branched roots. Slope collapse was triggered by raising the water table while soil displacements, pore-water pressures, and root strains were measured. The mode of failure was changed by the presence of roots from a progressive block failure to translational failure. The tests revealed how axial strains and bending strains were mobilized in the roots and how the roots influenced the slope failure mechanism. Different limit equilibrium slope stability calculations were performed at slope failure conditions to quantify the amount of reinforcement provided by different root types. These measured root reinforcement contributions were compared with those predicted according to common root reinforcement models. A reinforcement calculation method allowing for root pull-out was found to give the best agreement.

Root tensile strength of 3 typical plant species and their contribution to soil shear strength; a case study: Sasumua Backslope, Nyandarua District, Kenya

The effect of root reinforcement depends on the morphological characteristics of the root system, the tensile strength of individual roots, the soil-root cohesive strength, and the distribution of the root system in the soil. This research looks into Sasumua Backslope in Kenya, where a great deal of erosion is responsible for large soil losses. Shallow mass movements are evident throughout the slope. Root reinforcement effect of nine typical species was assessed, using Wu et al. (1979) model. The plant species comprised of shrubs (Atriplex halimus), grasses (Pennisetum clandistenum and Themeda triandra), and tree ferns (Asparagus species). Physical counting of roots per depth class was conducted to obtain root area ratio (RAR) values of the individual species. For each species, single root specimens were sampled and tested for tensile tests in the laboratory using the Hounsfield Tensometer apparatus. Maximum RAR values were located within 0.1 m for all the species, with maximum rooting depth of 0.7 m for fern tree. Shrubs species showed high RAR values between 0.1 &#8211; 0.3 m depth. Tensile force increases with diameter. Generally shrubs break at high tensile force (160 N maximum), followed by tree ferns (maximum 90 N) and lastly grass (maximum 75 N). Root tensile strength decreases with increasing root diameter, and follows a power law equation of the form . Generally, tensile strength can be well predicted by root diameter. The maximum root tensile strength values recorded was 39 N/mm2 for grass. The results presented in this paper contribute to expanding the knowledge on root resistance behavior and on root density distribution within the soil. The studied location has allowed the implementation of soil&#8211;root reinforcement models initially used by Wu et al. (1979) and the evaluation of the vegetation contribution to soil stability.

An analytical fiber bundle model for pullout mechanics of root bundles

[1] Roots in soil contribute to the mechanical stability of slopes. Estimation of root reinforcement is challenging because roots form complex biological networks whose geometrical and mechanical characteristics are difficult to characterize. Here we describe an analytical model that builds on simple root descriptors to estimate root reinforcement. Root bundles are modeled as bundles of heterogeneous fibers pulled along their long axes neglecting root-soil friction. Analytical expressions for the pullout force as a function of displacement are derived. The maximum pullout force and corresponding critical displacement are either derived analytically or computed numerically. Key model inputs are a root diameter distribution (uniform, Weibull, or lognormal) and three empirical power law relations describing tensile strength, elastic modulus, and length of roots as functions of root diameter. When a root bundle with root tips anchored in the soil matrix is pulled by a rigid plate, a unique parameter, , that depends only on the exponents of the power law relations, dictates the order in which roots of different diameters break. If 1, large roots break first. When = 1, all fibers break simultaneously, and the maximum tensile force is simply the roots' mean force times the number of roots in the bundle. Based on measurements of root geometry and mechanical properties, the value of is less than 1, usually ranging between 0 and 0.7. Thus, small roots always fail first. The model shows how geometrical and mechanical characteristics of roots and root diameter distribution affect the pullout force, its maximum and corresponding displacement. Comparing bundles of roots that have similar mean diameters, a bundle with a narrow variance in root diameter will result in a larger maximum force and a smaller displacement at maximum force than a bundle with a wide diameter distribution. Increasing the mean root diameter of a bundle without changing the distribution's shape increases both the maximum force and corresponding displacement. Estimates of the maximum pullout forces for bundles of 100 roots with identical diameter distribution for different species range from less than 1 kN for barley (Hordeum vulgare) to almost 16 kN for pistachio (Pistacia lentiscus). The model explains why a commonly used assumption that all roots break simultaneously overpredicts the maximum pullout force by a factor of about 1.6–2. This ratio may exceed 3 for diameter distributions that have a large number of small roots like the exponential distribution.

Reinforcement of Simulated Immature Roots Restored with Composite Resin, Mineral Trioxide Aggregate, Gutta-percha, or a Fiber Post after Thermocycling

Introduction The purpose of this study was to evaluate the fracture resistance after thermocycling of simulated immature teeth restored with composite, a fiber post, mineral trioxide aggregate (MTA), or gutta-percha. Methods Eighty-four primary bovine mandibular incisors were divided into 7 groups (n = 12). Negative controls received no treatment. Teeth in all other groups were prepared to an internal diameter of 1.75 mm. After placement of 4-mm apical barrier of MTA, the canals were filled with their respective test materials to the facial cementoenamel junction. For the fiber post group, a fiber post was fitted to extend from the MTA barrier to 2 mm below the incisal edge and was cemented with Build-It FR. The positive controls were left unfilled. The access openings were filled with BisFil II composite. All teeth were then thermocycled for 500 cycles at 5°C and 55°C with a 30-second dwell time and 5-second transfer time. Each root was horizontally fractured through the test material by using an Instron Universal Testing Machine, and the peak load to fracture was recorded. The data were analyzed with analysis of variance and Tukey post hoc tests ( P < .05). Results and Conclusions Thermocycled composite was not significantly stronger than gutta-percha and MTA. The only material that significantly strengthened the simulated immature teeth was the fiber-reinforced composite with a fiber post.

Spatial statistical modeling of shallow landslides—Validating predictions for different landslide inventories and rainfall events

Statistical models that exploit the correlation between landslide occurrence and geomorphic properties are often used to map the spatial occurrence of shallow landslides triggered by heavy rainfalls. In many landslide susceptibility studies, the true predictive power of the statistical model remains unknown because the predictions are not validated with independent data from other events or areas. This study validates statistical susceptibility predictions with independent test data. The spatial incidence of landslides, triggered by an extreme rainfall in a study area, was modeled by logistic regression. The fitted model was then used to generate susceptibility maps for another three study areas, for which event-based landslide inventories were also available. All the study areas lie in the northern foothills of the Swiss Alps. The landslides had been triggered by heavy rainfall either in 2002 or 2005. The validation was designed such that the first validation study area shared the geomorphology and the second the triggering rainfall event with the calibration study area. For the third validation study area, both geomorphology and rainfall were different. All explanatory variables were extracted for the logistic regression analysis from high-resolution digital elevation and surface models (2.5 m grid). The model fitted to the calibration data comprised four explanatory variables: (i) slope angle (effect of gravitational driving forces), (ii) vegetation type (grassland and forest; root reinforcement), (iii) planform curvature (convergent water flow paths), and (iv) contributing area (potential supply of water). The area under the Receiver Operating Characteristic (ROC) curve ( AUC) was used to quantify the predictive performance of the logistic regression model. The AUC values were computed for the susceptibility maps of the three validation study areas (validation AUC), the fitted susceptibility map of the calibration study area (apparent AUC: 0.80) and another susceptibility map obtained for the calibration study area by 20-fold cross-validation (cross-validation AUC: 0.74). The AUC values of the first and second validation study areas (0.72 and 0.69, respectively) and the cross-validation AUC matched fairly well, and all AUC values were distinctly smaller than the apparent AUC. Based on the apparent AUC one would have clearly overrated the predictive performance for the first two validation areas. Rather surprisingly, the AUC value of the third validation study area (0.82) was larger than the apparent AUC. A large part of the third validation study area consists of gentle slopes, and the regression model correctly predicted that no landslides occur in the flat parts. This increased the predictive performance of the model considerably. The predicted susceptibility maps were further validated by summing the predicted susceptibilities for the entire validation areas and by comparing the sums with the observed number of landslides. The sums exceeded the observed counts for all the validation areas. Hence, the logistic regression model generally over-estimated the risk of landslide occurrence. Obviously, a predictive model that is based on static geomorphic properties alone cannot take a full account of the complex and time dependent processes in the subsurface. However, such a model is still capable of distinguishing zones highly or less prone to shallow landslides.

Root site occupancy modelling of young New Zealand native plants: implications for soil reinforcement

Plants are widely used in soil conservation to control and prevent erosion on hillslopes and on riverbanks. Previous research has shown the mechanical root reinforcement on soil stability can be considerable. However, land and forest managers still require information and simple tools to enable them to determine how and when a species becomes effective in terms of soil stabilisation. This paper uses root length data from a trial of young New Zealand trees and shrubs to develop a simple model to account for the spatial occupancy of a planting site by roots, and by implication their potential strength contribution to soil reinforcement. It is developed by calculating root surface area in contact with the soil to obtain an effective radius of the root spread about the stem. The approach generates a set of coefficients that are unique to a species for a given site which can then be used in the generalised model to predict root site occupancy, which is taken as a proxy for when soil reinforcement is attained. This information can then be used to assess effectiveness of different species mixes in planting plans.