Displacement Monitoring at Verrand High Reinforced Soil Structure - Reinforced Soil Engineering: Advances in Research and Practice - page 121

3 THE REINFORCED SOIL

The reinforced soil included nonwoven geotextiles reinforcements and a facing
system, resulting in a completely grassed surface, once construction completed.
The facing system is patented.
The basic element of the selected facing technology are 0.5- or 0.6-m-high,
L-shaped forms made by a welded steel wire mesh. Such forms are left in place,
after compaction. Each form element is bent to the angle selected for the slope.
Short steel tiebacks prevent significative deformation of the wire mesh, during
compaction of adjacent lifts. A light woven geotextile is placed inside the form to
retain the soil. The fill material is usually spread and compacted in lifts, whose
thickness is half the form height. Lifts stop some 0.4m away from the form. The
space between the lifts and the forms is filled with topsoil, to support vegetation.
The surface is finally hydroseeded so that it becomes completely and

permanently grassed in a short time (Fig. 1) .
The reinforcements used at Verrand were anisotropic nonwoven,
continuous filament, needle-punched, polyester (PET) fiber geotextiles, of
three grades, manufactured by Fritz Landolt A.G., Switzerland. The nominal
tensile strengths of the geotextiles were 40, 100 and 120 kN/m, and their main
characteristics are summarized in Table 1.
The fill material placed within the reinforced section was well-graded,
crushed rock with a relatively large sand and silt fractions, obtained by
processing tunnel muck. The material mainly came from tunneling in schists. The
tunnel muck was first crushed in order to reduce its maximum grain size to 150-
200mm and then mixed with material obtained from open-air excavations. A
relatively high content in sand and silt fines was added to reduce damage to the
reinforcements.
The backfill was basically the same material with maximum size in the
order of 500 mm.

Table 1 Main Characteristics of Geotextiles FLN-TEXA Used as Reinforcement at
Verrand HRSS

Machine
direction

Transverse
direction

Strength
[kN/m]

Elongation
[%]

Strength
[kN/m]

Elongation
[%] Mass [g/m 2 ]

Type

350 350 48.5 36.8 21.8 37.6

1000 900 115.5 38.3 47.8 36.2

1200 1050 132.7 40.1 55.4 39.6