Reinforcement over soft soils with high-strength geogrids This article summarizes the two instances where a basal reinforcement may be included underneath an embankment and demonstrates those uses with two case studies. FIGURES 2a-2e Potential modes of failure considered in the design process (British Standard BS 8006:2010) Basal reinforcement over soft soils The construction of an embankment over soft soils is influenced by the bearing capacity and the shear resistance of the foundation soils. Its stability is most critical during construction, because the relatively low permeability of the soft foundation does not allow full consolidation in the normal time scale of construction. A geosynthetic reinforcement may be placed at foundation level to prevent shear failure both in the embankment fill and in the foundation soil. The factored design strength of this reinforcement should be greater or equal to the design load at any instant in time, during the period between the end of construction and the complete consolidation of the soft foundation. The design approach for basal FIGURE 3 Reinforcement layout in the reinforced granular mattress (RGM) reinforcement over soft soils is to verify the potential mode of failure for the following ultimate limit states: local stability of embankment fill, rotational stability of the embankment, lateral sliding of the embankment, foundation extrusion stability and overall stability (Figures 2a-2e). Total foundation settlements are not directly affected by a geosynthetic reinforcement layer, which may change the stress distribution leading to a possible reduction in differential settlements. Nevertheless, the embankment settlements need to be checked to avoid excessive geosynthetic strain levels resulting in an increase in tensile strain and load. One form of basal reinforcement is a reinforced granular mattress (RGM), which is a 3D structure fabricated directly on the soft foundation soil with geogrid 16 Geosynthetics | February March 2022