# Geosynthetics August/September 2021 - 16

```Geosynthetic-reinforced column-supported embankments: Improving practice with better theory
Theoretical models
Based on experimental and numerical
studies, researchers have proposed different
soil arching models (Figure 4) and
their corresponding calculation methods
for reduced stress due to soil arching.
These models can be sorted into three
groups in terms of their deformation
patterns: (a) curved, (b) triangular and
(c) vertical. However, McGuire and Filz
(2008) found that these models resulted
in significant differences in the calculated
vertical stresses on the geosynthetic.
As a result, the tensile forces in the geosynthetic
calculated by these models differ
by 10 times, which is not acceptable for
practice. Han (2021) attributed one of
the main reasons for these differences to
the fact that different stages of soil arching
were assumed in the development
of these models. Iglesia et al. (1999) and
Han et al. (2017) concluded soil arching
progressively develops with the displacement
from curved, triangular to vertical
deformation patterns. Han (2021) found
that the minimum soil arching ratio corresponds
to the concentric soil arching,
while the ultimate soil arching ratio corresponds
to the vertical soil arching; therefore,
he linked these two important states
to the following two representative soil
arching models to generate the simplified
GRC: (1) the concentric arch model
developed by van Eekelen et al. (2013)
and (2) the adapted Terzaghi arch model
proposed by Russell et al. (2003). Both
models considered the three-dimensional
effect of column patterns.
In addition to soil arching, design of
(a) Curved
FIGURE 4 Soil-arching models
(b) Triangular
(c) Vertical
Normalized stress
/( H+q0)
1.0
ps
s
s
Solution
Determined by
the concentric
soil arch method
Minimum
Subsoil + Geosynthetic
Geosynthetic
Subsoil
Ultimate
Normalized displacement, /(s-a)
FIGURE 5 Proposed unified solution
16
Geosynthetics | August September 2021
!
a
q0
H
Determined by
Terzaghi method
GRCS embankments must determine
the required maximum tension in the
geosynthetic according to the tensioned
membrane effect. Han and Gabr (2002)
found that the maximum tension in the
geosynthetic above columns occurred
at the edge of columns when a single
geosynthetic was used. This finding was
confirmed by several later studies. Russell
et al. (2003) and van Eekelen et al. (2013)
both considered the net applied pressure
(i.e., the difference between the pressures
above and below the geosynthetic) on
the geosynthetic that is eventually carried
by the reinforcement strips between
columns so that the higher tension in
the geosynthetic is calculated using the
parabolic method.
Furthermore, the column/subsoil
interaction should be considered in the
design. The downdrag force between
columns and subsoil reduces the vertical
stresses in the subsoil with depth.
At a certain depth (called the neutral
plane), the downdrag force becomes zero
when the columns and the soil have the
same deformation. The distribution of
the downdrag force and the depth of
the neutral plane depends on the stress
on the subsoil and the properties of the
columns and the subsoil, including the
```

# Geosynthetics August/September 2021

Geosynthetics August/September 2021 - Cover1
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Geosynthetics August/September 2021 - Cover3
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