Geoscience Reference
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4 WRAPPED FACED GEOSYNTHETIC REINFORCED
FEATURES
Several features where the facing was established by overwrapping the geotextile
reinforcement were constructed. Many of these features had facing inclinations
smaller than 70
and consequently are reinforced slopes. All of them were
constructed for private owners. The most widely used application for these
geosynthetic-reinforced slopes is rehabilitation of landslides or provision of flat
areas for structures constructed on potential landslide areas. These applications
include mostly housing projects and creation of large storage areas.
8
5 AN EXPERIMENTAL WALL
In 1992, a three-year research project was developed to construct a full-scale
geotextile reinforced retaining wall in Istanbul. This wall project was funded by
the U.S. National Science Foundation, the Scientific and Technical Research
Council of Turkey, and the Bogazici University Research Fund. The project was
unique in its focus on field measurements and was the first known reinforced wall
where the backfill consists of lime treated clay. The wall had a trapezoidal face
section with upper and lower bases of 8.8m and 18.2m, respectively. The wall
consisted of 6 layers with a total height of 5.25m. The upper three reinforcement
layers were 3.85m long, while the lower ones were 2.1 m. Natural clay available
at the site was mixed with 4% lime. The selection of this percentage was based on
laboratory tests, which indicated that 4% was the optimum mix percentage in
terms of strength and permeability characteristics.
The geosynthetic used as reinforcement was a nonwoven, needle-punched,
geotextile with a strip tensile strength of 5.9 kN/m and an equivalent opening size
of 0.13mm. No safety factor was applied to this strength. The Federal Highway
Administration method (Christopher et al., 1990) was followed for the design of
the wall. The wall was designed to fail by rupture under its own weight with a
safety factor of slightly less than 1. Throughout the project life, six Gl¨ tzl
pressure cells were used to measure the vertical pressure within the wall, and five
Gl¨ tzl pressure cells were used to measure the horizontal stresses. Deformations
were measured with a new developed technique, utilizing electronic coils.
An incremental surcharge load of 41 kPa was exerted at the top surface of
the wall, which did not bring the wall to failure. Based on the idea that saturation
of clay could result in both a significant loss of frictional strength and cohesion,
an attempt was made to bring the wall to failure by wetting it. Two large holes
were dug into the top surface of the wall and continuously filled with water.
During the filling process, the water leaked through the first layer of geotextile
material and drained horizontally away from the wall. It was clear that
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