Highway A31 foundation reinforcement

Geodren® for the foundation of Highway A31

Geodren® W-PP: woven PP geotextile for road foundation reinforcement, together with Geodren® N3 nonwoven geotextile for drainage and separation.

Problem

The completion of the southern section of Highway A31 required an in-depth study of embankment behavior, both in the short and long term. The study addressed stability in terms of ultimate and serviceability limit states.

The on-site soils, from a geotechnical standpoint, show considerable stratigraphic variability, both longitudinal and transverse. Engineers found a “”chaotic”” alternation of sands, silts and clays. This stratigraphic pattern is explained by the different deposition conditions of the waterways crossing the route.

The project therefore included a series of interventions on the laying plane of several sections of the new highway embankments. These interventions were necessary to ensure, at every stage of construction, compliance with the required safety coefficients for stability analysis. They also had to guarantee that settlements would stabilize within the planned timeframe along the entire route.

Solution

To meet the performance requirements (in terms of deformability) for the planned highway embankment, designers specified a foundation package as follows.

For embankments up to 2 m high:
– excavation of about 40 cm for embankment heights below 1.40 m, and about 80 cm for heights of 1.40 m or above;
– surface consolidation (about 30 cm) of the laying plane, using 3% lime stabilization by weight (scarification, spreading, mixing and rolling/finishing);
– laying of Geodren® W-PP 105, a woven polypropylene geotextile;
– a treatment layer (A1 and A2-4 materials) up to the original ground level;
– the embankment body, built with A1 and/or A2-4 soils.

For embankments over 2 m high:
– deep stabilization column treatments using “”deep mixing”” technology;
– excavation of about 50 cm from the original ground level;
– laying of a woven polypropylene geotextile with a tensile strength of 100 kN/m or higher, type Geodren® W-PP 105;
– a treatment layer (A1 and A2-4 materials) up to the original ground level;
– laying of Geodren® W-PP 105, a woven polypropylene geotextile with a tensile strength of 100 kN/m or higher;
– a layer of Geodren® N3, a nonwoven polypropylene geotextile for drainage and separation;
– the embankment body, built with A1, A2-4, A2-5 and A2-6 soils.

As a result, engineers increased the bearing capacity of the foundation soil and significantly reduced the amount of excavation required.