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 Reinforced earth technology is one of the most significant civil engineering innovations
of the last three decades. Deependra Chauhan, Operations Head, RECo (India),
Freyssinet-Soletanche Group, presents an interesting case study.
The National Capital Region
board has prepared
'Regional Plan 2021' for
overall development of
NCR region. The regional plan
envisages infrastructure development
in terms of power, water,
telecommunications, sewerage,
drain, irrigation, construction of
peripheral expressways, beautification
of entry points to Delhi etc.
As a pioneering step to achieve
the identified goal to beautify the
entry points related to history of
Delhi, the first major entry point of
NH-1 (i.e. the historic Sher Shah
Suri Marg) is being developed as
a memorial at Singhu border. The
memorial will be dedicated to
Guru Teg Bahadur, the ninth Sikh
Guru who was beheaded with his
disciples at Sisganj Gurdwara and
laid to rest at the Rakabganj Gurdwara
in the city.
The theme of the memorial is
based on the Nishan Sahib which
is a sacred emblem of the Sikh
guru and can be seen at every gurdwara.
The memorial will have a
24-metre high central pylon made
of stainless steel and will be lit on
top with laser lights, and this
pylon will bear semblance to the
Nishan Sahib. At the base of the
pylon there will be eight petals
made of copper, elliptical in form,
signifying the selflessness of the
guru. His three disciples who
were tortured to death will be represented
by three stainless steel
arches approximately 16 metres
in diameter and placed in a semicircular
design. The 10 monoliths
around the pylon will represent
the 10 Sikh gurus and their teachings
will be engraved on same.
Reinforced earth technology
Reinforced earth was invented
and pioneered by Henry Vidal, a
French architect, during the
1960s. He performed numerous
tests on full-scale models and
assembled comprehensive documentation
on various materials
that could be used in reinforced
earth construction. He evolved a
unique composite material
formed by the interaction of frictional
soil and reinforcing strips
and called it reinforced earth. He
established a company called
Terre Armee Internationale
(Groupe TAI).
The concept of reinforced earth
is similar to reinforced concrete,
in which tensile load carrying elements
are introduced in the earth
mass to improve its load carrying
properties. Stresses produced
within the earth mass are resisted
by reinforcing corrosive resistant
material (like steel or
synthetic/semi-synthetic material
and maybe any other suitable
organic material), which are
transferred via friction. The volume
thus formed of earth mass
thus formed with distributed steel
strips becomes its own supporting
structure. A form of facing
cover consisting of discrete concrete
elements called precast
panels is provided for durability
and aesthetic appearance to the
structure. Besides, this unique
shape of the panel caters to maximum
transversal, vertical and
longitudinal flexibility.
However, it is to be noted that
the concept of Henry Vidal is just a
modern form of reinforcing soil.
Before the reinforced earth concept
as initiated by Henri Vidal
becomes widely accepted,
ancient people had used vegetation
to enhance slope stability e.g.
the Great Wall in China, where
twigs of tamarisks (a deciduous
shrub) were used; the ziggurats
(Sumarian temples) in
Mesopotamia used reeds. In
India's countryside, straws of
wheat or rice are mixed with mud
mortar or with cow dung plaster to
make houses.
Significant innovation
Reinforced earth technology is
one of the most significant civil
engineering innovations of the
last three decades. Continual
innovations represent the evolution
of the art of reinforced earth
technology into new area of application
and it is also possible to
develop aesthetic solutions to
address special site conditions
and designers requirement.
Although introduced in India
mainly in the last decade, applications
of reinforced earth technology
remain limited as an alternative
to retaining walls, mainly in
bridges and flyover approaches.
This project has a most significant
technological feature in the form
of application of mechanically stabilised
soil technique i.e. reinforced
earth walls for outer
embankment of the memorial as a
landscape and as well as an architectural
enhancement. This is the
first of its kind in India. The outer
of the memorial is approximately
an 8-metre high embankment
consisting of (i) A part height (4 to
5m) of standard reinforced earth
wall with rectangular and square
panels facia with alternate
arrangement of architectural finish
and stone claddings, and (ii)
Atop is a vegetation friendly variant
of reinforced earth having a
facing element of light steel bar
mesh with a stabilised steep slope
of varying height from 0 to 6 m.
The comparatively low cost, fast
speed of installation, construction
ease, geometrical shape articulations
and load bearing quality of
the reinforced earth made it easily
adaptable to the specific requirement
of the project. The innovation
at this memorial represents
the evolution of the art of reinforced
earth technology in the
area of landscaping and aesthetics
structures in India.
RECo-India i.e. Reinforced
Earth Company (India) Ltd, a subsidiary
of Freyssinet-Soletanche
Group in India, actively participated
with the architecture firm in
developing the concept. RECo-
India was required to work closely
with the project architects and to
be ready to react quickly to continuously
changing various combinations
as they occurred. Several
permutations and combinations
were tried and later on, it was
decided to blend the two variants
of reinforced earth to achieve the
architectural enhancements with
a value engineering alternative.
RECo-India provided the concept
of mechanically stabilised
embankment, technological
knowhow, design, supply of all
specialised materials, on-field
technical and constructional
assistance, advices etc. These
types of walls are normally considered
where the structure is in
a fill situation; otherwise it will be
necessary to excavate base
widths greater than what would
normally be required for a mass
gravity structure.
High adherence (HA) galvanised
steel strip has been used
to design the vertical retaining
wall with precast RCC TerraQuad
rectangular as well as square panels.
The high tenacity polyester
geogrids have been used to
design the atop 70° slope with
green facing.
Unique design
The design of the structure was a
challenge due to its complex
geometry and also it is the first of
its kind where two different types
of soil reinforcement materials
have been amalgamated to construct
the structure. Designing
oval shape walls represented a
challenge.
Due to this unique geometry
there is no standard software or
specific design methodology
available to design such structure.
Hence, the design of reinforced
soil structure is based on three different
standards i.e. BS 8006-1995
for static design and AFNOR NFP
220-94 for seismic design of vertical
retaining wall using steel
strip, and FHWA for both static
and seismic design of top slope
using geogrid as reinforcement.
Then the overall stability is
checked based on basic soil
mechanics theory. The design is
done in three steps-design of reinforced
soil wall, design of top
slope structure, and the overall
stability check by slip circle
method. Three different softwares
have been used to design the
structure viz. Groupe TAI
VALDEZ 2.3 software for vertical
wall with steel strip considering
top slope as dead load surcharge
of 56 kPa. Then the top slope is
designed using commercial software
ReSSA (2.0) and then the
overall stability is checked using
Talren 97 software.
The Reinforced group is continually
designing new panel surface
treatments to respond to
requirements of the project owners
and their architects. Reinforced
Earth Company provides a
variety of architectural finishes.
Form liners were used to create
pattern designed by the architects
of the projects, consisting of
broken rib finish with branching
flutes. Beside, some panels were
clad with red sand stone, which
were fastened with facia panels.
To give a matching effect, coping
of the panels was also made of
the red sand stone as can be seen
in figure 3.
Live vegetation for slope stabilisation
has been used since
primeval times. Amalgamation of
this practice with reinforced soil
techniques has given greater
dimension to slope stabilisation
concepts, though done in a
methodical manner. Delhi
observes an extreme variation of
weather temperatures. The
weather is almost arid with the
advent of summer season with
high intensity of hot winds. It was
therefore necessary that species
of plant should be selected which
will remain green perennially,
should have less maintenance
with vigorous growth, and form
good green foliage. Many alternatives
were thought of, like
Napier grass, Kolkata dhup
grass, and varieties of
vines/creepers. The idea of grass
was eventually dropped, as grass
would be prone to drying under
the influence of hot summer
winds or frost bite in winter and
could become susceptible to fire.
The vine, popularly called 'curtain
creeper' or Vernonia creeper,
was conclusively selected as it
gives a rich array of perennial
green foliage.
Summary
The project presented a unique
type of challenge for the execution
of a new idea to enable aesthetic
and technical needs on a quicker
basis. Successful civil engineering
projects are those which combine
excellent performance with
attractive appearance. The reinforced
earth remains an exciting
material that continues to elicit
enthusiastic and innovative
thoughts, as it has limitless aesthetics
and architectural possibilities
which can reflect the designer's
attention.
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