Résumé
Investigating the contribution of roots in the reinforcement of slopes against shallow landslides needs to better understand the local root-soil interactions at the root and root-soil block scales. Many experimental studies were carried out in order to quantify the contribution of roots to soil shear strength. Most of these experiments consist in shearing rectangular parallelepiped soil blocks (shear tests) with and without roots and deducing a “root additional cohesion-friction angle” from the analyses of resulting response curves. However it is often difficult to interpret the results without considering the effect of each individual root as well as the group effect involved by neighbor roots. Finite Element Models (FEM) can help analyzing the distribution of stresses and strains (elastic or plastic) within a heterogeneous solid body submitted to external forces. The aim of this study is to present such a FEM that simulates shear tests of root-soil blocks, and to analyze numerically the contribution of root elements on the mechanical response of the global system. Two modeling approaches, i.e. a standard lagrangian approach and an Euler explicit approach, were developed and compared using the Abaqus software (www.simulia.com). 3D numerical results were compared with real shear tests done separately with reinforcement elements (plastic coated copper wires) embedded in the soil. The effect of an increase in the stiffness of the wires on soil shear resistance was analyzed. The main results are: 1- the Euler explicit method is suitable to simulate shear tests involving large distortion; 2- simulations explained why real shear tests exhibited lower shear strength of “reinforced” soils compared to bare soils, and thus can help designing more suitable experiments; 3- a variation in the bending stiffness of wires modifies the stiffness and shear resistance of reinforced soil blocks through a modification of the ratio between normal and shear stress components involved during their deformation.