A31 highway basal reinforcement

Italy, Rovigo-Vicenza
PP woven geotextile as reinforcement of road foundations and PP nonwoven geotextile as anti-capillary function

Problem:
completion of the southern section of highway A31 has led to an in-depth study of the road embankment stability behaviour, both short and long term, in terms of ultimate and operating limit states.
In fact, from a geological point of view, the soil on site is significantly stratified, both length and cross wise, with “chaotic” alternating of sand, loam, and clay.
This stratigraphic trend can be explained by the various deposit conditions of the waterways that cross the section.
The project therefore called for a series of works on the lay plane of a few sections of new highway embankments. These are considered necessary in order to ensure, in any case and in all phases of work, that the minimum safety coefficients required according to the stability analysis are respected, or to allow the subsidences, in time, to be exhausted uniformly and in specific areas along the section.

Solution:
To meet the performance characteristics required (in terms of deformation) for the designed highway embankment, the designers have called for a package of turf removal and amelioration as follows:

• for embankments lower than or equal to 2 m: excavation of about 40 cm, for embankments lower than 1.40 m and about 80 cm for embankments higher than or equal to 1.40 m; surface consolidation (about 30 cm) of the laying plane, through lime stabilisation at 3 weight percent (scaring, spreading, blending, and rolling/finishing); laying Geodren®W-PP 105, polypropylene woven geotextile; the body of the embankment in type A1 and/or A2 soil.
• for embankments higher than 2 m: deep stabilizing columns using “deep mixing” technology; excavation of about 50 cm of the original ground level; laying of a polypropylene woven geotextile with tensile strength equal to or greater than 100 kN/m such as Geodren®W-PP 105; a recovery frame (material A1 and A2-4) to the original ground level; laying of Geodren®W-PP 105, polypropylene woven geotextile with tensile strength equal to or greater than 100 kN/m; a layer of Geodren®N3,  polypropylene nonwoven geotextile with anti-capillary function; and the body of the embankment with soil types A1, A2-4, A2-5, and A2-6.

In this way the embankment foundation bearing capacity was increased with less soil excavation.