We developed a new construction technique called Hybrid Sandwiched Reinforcement (HBS) method, by which thin sand layers are placed above and beneath a geosynthetic fabric to increase the mechanical potential of cohesive soil embankments and foundations. This reinforcement method improves reinforcement and maintains hydraulic conductivity. Successive to the authors' previous works, this paper describes numerical analysis of embankment with and without reinforcement and a sand layer. Results from numerical analyses are interpreted with emphasis on improved toughness of HBS-reinforced embankments. Results clarified that HBS not only controls embankment deformation, it improves toughness using placement of geosynthetics in an embankment comprising cohesive soils such as Kanto loam of volcanic-ash origin. Regarding improved toughness of HBS earth structures, the numerical analysis results show that the sandwich structure improves the cohesive soil embankments' bearing capacity and stiffness. Placement of thin sand layers above and below non-woven geosynthetics and their high potential for drainage make non-woven geosynthetics more suitable for sandwiched earth structures consisting of cohesive soils, particularly cohesive soils of volcanic origin. Results are superior to those of geonets or geogrids, which are widely used for sandy soil reinforcement.