Geogrids are extensively used for reinforcing paved and unpaved road bases on soft soils. Anyway the present design methods provide no indication for the number of required layers and the mechanical characteristics of reinforcing geogrids. Hence a new design method has been developed which affords the design of geogrids for road base reinforcement, based on a 4 layers model: asphalt (binder and wearing course), in case of paved roads; base, subbase, subgrade. Once the base and/or subbase thickness has been defined with one of the available methods (as an example: Giroud – Han method, Leng- Gabr method, etc.), the proposed design method affords to calculate the tensile forces in reinforcing geogrids generated by: self weight of the different layers; wheel load of heavy vehicles; membrane effect at the base (or subbase) – subgrade interface. It is then possible to set the number and the mechanical characteristics of geogrid layers required for absorbing the horizontal forces generated by the above listed mechanisms. Hence the proposed design method affords the design of geogrids in the safe construction of paved and unpaved roads on soft soil.
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