A generic form of fibre bundle models for root reinforcement of soil

Abstract

Purpose The mechanical contribution of plant roots to the soil shear strength is commonly modelled using fibre bundle models (FBM), accounting for sequential breakage of roots. This study provides a generic framework, able to includes the many different existing approaches, to quantify the effect of various model assumptions. Methods The framework uses (1) a single model parameter determining how load is shared between all roots, (2) a continuous power-law distribution of root area ratio over a range of root diameters, and (3) power-law relationships between root diameters and biomechanical properties. A new load sharing parameter, closely resembling how roots mobilise strength under landslide conditions, is proposed. Exact analytical solutions were found for the peak root reinforcement, thus eliminating the current need for iterative algorithms. Model assumptions and results were validated against existing biomechanical and root reinforcement data. Results Root reinforcements proved very sensitive to the user-defined load sharing parameter. It is shown that the current method of discretising all roots in discrete diameter classes prior to reinforcement calculations leads to significant overestimations of reinforcement. Addition of a probabilistic distribution of root failure by means of Weibull survival functions, thus adding a second source of sequential mobilisation, further reduced predicted reinforcements, but only when the reduction due to load sharing was limited. Conclusion The presented solutions greatly simplify root reinforcement calculations while maintaining analytical exactness as well as clarity in the assumptions made. The proposed standardisation of fibre bundle-type models will greatly aid comparison and exchange of data.

Intra‐ and inter‐specific variation in root mechanical traits for twelve herbaceous plants and their link with the root economics space

“…Relationships between any mechanical trait and root diameter were poorly captured by the power law function that is usually used to describe such relationships (Meijer 2021) (Fig. 2, 3, 4, 5).…”

“…At the intraspecific level, we performed power law regression fits to explore the relationships between mechanical metrics and root diameter for each species (Cohen et al 2011, Meijer 2021) (Eq. 1): …”

“…At the intraspecific level, root mechanical traits are highly variable and are usually characterized as a function of root diameter (de Baets et al 2008, Burylo et al 2011, Ghestem et al 2014, Ji et al 2020). For example, many studies have shown that a negative power law relationship occurs between root tensile strength and diameter (Genet et al 2005, Fan and Su 2008, Mao et al 2012, Ghestem et al 2014, Ji et al 2020, Meijer 2021), suggesting that finer roots are stronger (in terms of material) than more coarse roots. This phenomenon has been attributed to differences in root structure, with thinner roots possessing more cellulose per dry mass than coarser roots (Zhang et al 2014, Zhu et al 2020).…”

Effect of freeze‒thaw cycles on root–Soil composite mechanical properties and slope stability

“…According to the above test results, combined with the research of other scholars, the attenuation mechanism of the root-soil composite strength due to freeze-thaw action is briefly summarized below (Fig 13 ): 1. Root reinforcement without freeze-thaw action: Without freeze-thaw action, a root-soil composite, in which the roots are intertwined, forms a uniform and effective "network" support system of roots [35][36][37]. At the same time, there is strong cohesion between soil particles and between roots and soil particles.…”

Mechanical Characteristics of Rice Root–Soil Complex in Rice–Wheat Rotation Area

“…Feng et al [18] took a root-soil complex composed of arbor roots and unsaturated red clay as the research object, and studied the influence of soil water content, Agriculture 2022, 12, 1045 2 of 15 the angle between parallel double roots, and shear surface on shear strength. Meijer [19] studied a common model framework that quantifies the impact of various model assumptions through existing methods; Liu et al [20] analyzed the micro-structural characteristics of root surfaces of Caragana and Overlord shrubs, soil surface in contact with the roots, and soil surface in contact with no roots and their influence on friction characteristics of the root-soil interface by means of scanning electron microscope. Zheng et al [21] carried out shear tests on the rice root-soil complex on a universal material-testing machine with a self-made shear test device.…”