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

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.

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. 

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. 

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.   

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.