Retaining structure in reinforced soil, Highway A3

Edilgrid® for the reinforced slope, Highway A3

Edilgrid®: woven polyester geogrids with PVC coating for the construction of reinforced soil slopes.

Problem

The upgrade of the A3 Salerno-Reggio Calabria highway requires various types of retaining structures. These include tie-back walls, reinforced concrete retaining walls and reinforced soil. For this type of work, Geosintex supplied the contractor SIS scpa with materials, technology and technical support. The goal was the construction of the reinforced soil structure named TR23. This structure has a maximum height of 16.90 m.

The site soil consists of two layers, defined as UG6a and UG6b. The first layer, with a maximum thickness of about 4 m, consists of flysch-like formations alternating brown and black claystones, clays and siliceous calcilutites. This material has relatively modest mechanical properties, which required deep ground improvement with the burial of the first courses of reinforced soil. Below the first clay layer lies the UG6b unit, a clay flysch very similar to UG6a but with better mechanical properties.

Solution

Engineers built a reinforced soil structure with Edilgrid® as a retaining structure for the road surface. The solution ensures the stability of the road platform while also allowing excellent environmental integration. Edilgrid® is a PET geogrid with PVC coating, with a tensile strength of 35-55-80-110 kN/m and low elongation at break.Edilgrid® is a PET geogrid with PVC coating, with a tensile strength of 35-55-80-110 kN/m and low elongation at break. In addition, it offers low creep elongation, good durability and resistance to mechanical damage, as well as extreme ease and speed of installation.

Starting from ground level, the anchor length of the first geogrid layers is Lanc=14.00 m. TR23 is a reinforced soil structure that falls into the reinforced slope category, with a face inclination of 63° and a layer thickness of 65 cm. It has a face inclination of 63° and a layer thickness of 65 cm.

It consists of three tiers. The first starts at ground level with a height of 7.15 m and is followed by a 1.0 m berm, a constant measurement for the other berms as well. The second tier follows, 4.55 m high, along with its berm. Finally, the last tier reaches a height of 5.20 m. The structure then continues with a small 1.30 m embankment at a 34° incline. The reinforced soil structure has a linear length of about 216 m, with a surface area of 2,500 m².

Given the considerable height of the structure and the complex stratigraphic conditions, engineers also carried out numerical analyses, in addition to the standard checks. This provided a better understanding of the structure’s behavior. After a short time, the face was fully re-vegetated, and the structure blends perfectly into the natural environment.