* The soil mass adjacent to the rock imprinting results in compression, while after a certain distance from the first contact point, the acceleration applied to the soil mass produces an outward horizontal movement equivalent to a tensile force being applied to the soil; at the limit between the compressed and the " tensioned " zone, cracks are formed; the soil mass is therefore separated into two parts. The tensile and pullout resistance of the reinforcement can contribute to avoid the failure due to outward displacement. * Available full-scale tests, FEM and DEM models clearly show that geogrids are able to " guide " the energy, so that the initial spherical shape is soon converted into a horizontal cone; outward displacements occur within this cone, leaving the remainder of the soil mass in place. * Available full-scale tests, FEM and DEM models also show that the stresses in the reinforcements have an important component in the direction parallel to the length of the embankment, beyond the compressed zone at the upstream face: this justifies the design assumption of also putting geogrid layers in such direction. * Both tests results and numerical models confirm that geosynthetic reinforcements are subject to high tensile forces, in many cases almost reaching the tensile resistance of the reinforcement used. But the impulsive www.GeosyntheticsMagazine.com 21http://www.layfieldgroup.com/cspe http://www.GeosyntheticsMagazine.com