Small-scale modelling of root-soil interaction of trees under lateral loads

Aim (1) To understand the tree root-soil interaction under lateral and moment loading using a physical modelling technique; (2) To detect the possible factors (e.g. root architecture, water condition, and stress level) influencing a tree's pushover behaviour; (3) To identify suitable scaling laws to use in physical modelling. Methods Two 1:20 scaled root models with different architectures (namely, deep and narrow, and shallow and wide) were reconstructed and 3D printed based on the field-surveyed root architecture data. Pushover tests were performed both in elevated-gravity (centrifuge 20-g) and normal-gravity (1-g) conditions. Results The shallow and wide model showed higher anchorage strength than the deep and narrow model. Regardless of the root architecture, the root anchorage strength measured from dry soil was higher than that from saturated soil. However, once the effective stress was the same, regardless of water conditions, the root anchorage strength would be the same. Conclusions The presence of water decreasing the soil effective stress and key lateral roots extending along the wind direction play a significant role on a tree's pushover resistance. Centrifuge tests showed comparable results to the field pullover measurements while 1-g model tests overestimated the root-soil interaction, which could be corrected for soil strength by using modified scaling laws. Keywords Root-soil interaction. Pushover . Centrifuge. Moment capacity. Root system architecture. Water condition Abbreviations ABS Acrylonitrile Butadiene Styrene CPT cone penetration test DBH diameter at breast height DSA direct shear apparatus ND narrow and deep (root model) PSD particle size distribution WS wide and shallow (root model) Plant Soi

Root Structure and Growth in Diverse Soils

Unlike most biofuel species, Jatropha curcas has promise for use in marginal lands, but it may serve an additional role by stabilizing soils. We evaluated the growth and structural responsiveness of young J. curcas plants to diverse soil conditions. Soils included a sand, a sandy-loam, and a clay-loam from eastern Mexico. Growth and structural parameters were analyzed for shoots and roots, although the focus was the plasticity of the primary root system architecture (the taproot and four lateral roots). The sandy soil reduced the growth of both shoot and root systems significantly more than sandy-loam or clay-loam soils; there was particularly high plasticity in root and shoot thickness, as well as shoot length. However, the architecture of the primary root system did not vary with soil type; the departure of the primary root system from an index of perfect symmetry was 14 ± 5% (mean ± standard deviation). Although J. curcas developed more extensively in the sandy-loam and clay-loam soils than in sandy soil, it maintained a consistent root to shoot ratio and root system architecture across all types of soil. This strong genetic determination would make the species useful for soil stabilization purposes, even while being cultivated primarily for seed oil

Effet d'une pente sur l'architecture et les propriétés mécaniques des systèmes racinaires de semis d'arbres

Le renforcement des sols par les racines est principalement déterminé par les paramètres suivants : la résistance des racines à la traction, la profondeur des racines et la quantité de racines par unité de sol. Pour comprendre comment le système racinaire d'adapte à une pente, nous avons étudiés la croissance de semis de deux espèces ayant des systèmes racinaires assez différents : le pin maritime (Pinus pinaster Ait.) et le robinier (Robinia pseudoacacia L). Les semis ont poussé dans des pots et des rhizotrons inclinés à différents angles, avec ou sans une perturbation mécanique qui imite l'effet du vent. Ensuite, l'architecture racinaire a été mesurée et des essais mécaniques et des analyses chimiques ont été réalisés. Nos résultats montrent que la pente influence significativement le développement de la plante et qu'il y a une forte interaction entre l'effet "pente" et l'effet "vent". Les racines les plus sollicitées mécaniquement sont les plus résistantes et cette résistance dépend du taux de cellulose. Les deux espèces montrent des stratégies différentes pour s'ancrer sur une pente. Ces résultats seront utiles pour alimenter des modèles d'ancrage racinaire et pour comprendre pourquoi certaines espèces sont mieux adaptées que d'autres pour stabiliser des sols.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF