Deformation mechanisms of deformable geosynthetics-reinforced barriers (DGRB) impacted by debris avalanches

This paper deals with geosynthetics-reinforced barriers conceived as protection works against debris avalanches, which are a dramatic threat for human life and structures. This kind of barrier is intended to be deformable under the impact and is here analysed for various cases of landslide velocity, impact duration and peak impact pressure. The latter is the sum of a dynamic component (velocity-dependent) and a static component (height-dependent). The barrier is conceived as a multilayered embankment, reinforced by geogrids wrapped around the facing. Both static and dynamic stress–strain analyses are performed through a commercial FEM code (Plaxis v. 8.5) to simulate the deformation mechanisms and the ultimate limit states. Four geometries of the barrier and four combinations of the materials are considered. The core of the barrier is made of coarse-grained material modelled as elastic-perfectly plastic with a non-associative Mohr–Coulomb yield criterion. The facing is 60° to 80° steep and sustained by an iron mesh here simulated as an elastic beam element. The geogrids are modelled as elastic traction-resistant elements. Frictional interfaces are considered at the soil–geogrid and the soil facing contacts. The displacements of the inner points and the global behaviour of barriers are evaluated over time. Out of four newly defined deformation mechanisms, local, global, combined or compound, only three principal scenarios are outlined: i) a global displacement along the base of the barrier, ii) a local yielding of soil combined with a global displacement of the barrier, or iii) a shifting of the reinforced layers along the geogrids with an acceptable performance of the whole barrier. Such results are discussed in relation to the geometry and the materials of the barrier, also taking into account the features of the impact loading.