Working again for Collini Lavori Spa, a road section required stabilisation due to poor subgrade. The initial schedule of works included a deep excavation and soil replacement. Collini asked if alternatives solutions were available, and Tailor Engineering provided an hybrid system able to limit the amount of excavation a combination of different geosynthetics products and recycled granular fill material.
This project used high strength geosynthetic (> 300 kN) and geocells. The ground improvement considered a flexible pavement with a minimum service life of 20 years. For the stabilisation of the road (embankment and subgrade) and thus for the dimensioning of geosynthetics, various approaches were considered. In particular, it was used a combination of calculation methods and available international guidelines.
In order to achieve adequate stabilisation of the subgrade, available guidelines recommend laying the geocell system in the lower layers that make up the pavement package. This allows an increase in the elastic modulus (increase in stiffness) of the layer confined by the geocells and an improvement in the secondary stiffness for all layers above it. The geocell were designed according to MIF (modulus improvement factor) approach achieving the required EV2 values. BS 8006-1 was considered for the inclusion of high strength geosynthetic. This product was specified to mitigate the typical problems of road embankments founded on soft soils, i.e.: limitation of differential settlements, foundation failure, instability of the embankment body.
