GEOSYNTHETICS AND
REINFORCED SOIL STRUCTURES
Prof K. Rajagopal
Department of Civil Engineering
IIT Madras, Chennai 600 036
e-mail: [email protected]
OUTLINE OF THE LECTURE
• Introductory remarks
• Historical background
• Types and functions of geosynthetics
Geosynthetics - Introduction
2/48
What is a geosynthetic ?
• Natural or artificial product that is used along
with soil in geotechnical constructions.
• Natural: coir, jute, hemp, etc.
• Artificial: p
polymeric
y
or metallic
Geosynthetics - Introduction
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Why geosynthetics ?
• Geosynthetics have entirely changed the way
geotechnical engineering is practiced.
practiced
• Innovative solutions to solve difficult problems
economically and expediently
• Enables the use of local materials – sustainable
solutions
• Unskilled labour can be employed
• Installation does not require heavy machinery
Geosynthetics - Introduction
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Use of coir mat to
promote vegetation
growth to prevent
surface erosion
Geosynthetics - Introduction
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Use of stone filled rope net gabions for shoreline stabilization at
S
Swami
i Narain
N i Temple,
T
l Tithal,
Tith l Gujarat
G j t
Geosynthetics - Introduction
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Irrigation canal lining by
using grout filled geocells
Geosynthetics - Introduction
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Narrow
stretch of
road
22m high geosynthetic soil retaining wall to widen a ghat road at Vijayawada
Geosynthetics - Introduction
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Landfill construction using geosynthetics
at HZL,
HZL Visakhapatnam to contain jerosite waste
Geosynthetics - Introduction
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Flexible Break water unit made of
geosynthetics
th ti – beach
b
h sand
d filled
fill d
bags in rope net gabions
Geosynthetics - Introduction
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REINFORCED SOIL
• Soil + reinforcement = reinforced soil
• Reinforcement:
Ancient: Tree branches, grass reeds, straw, roots of
vegetation bamboo
vegetation,
bamboo, tree trunks
Modern: Steel, polymeric, natural materials
• Soil is strong in compression & reinforcement is strong
in tension
• Combined product has much better engineering
properties than the individual constituents
• Reinforced soil concept is similar to that of reinforced
concrete
Geosynthetics - Introduction
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HISTORICAL
APPLICATIONS OF
REINFORCED SOIL
Geosynthetics - Introduction
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IS BEAVER THE FIRST CIVIL
ENGINEER ?
• Semi-aquatic rodent
• Expert
E pert builder
b ilder of Under
Underwater
ater d
dwellings/dams
ellings/dams
• Its dwellings use natural reinforcements
Geosynthetics - Introduction
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Ziggurats of Mesopotamia
• Constructed of clay
• A
Agar-Quf
Q f ziggurat,
i
t
bricks 130-400 mm high,
near Baghdad – 3000
reinforced with woven
years
yea
so
old
d
mats
t off reed
d laid
l id
• Originally believed to
horizontally on a layer of
be 80 m tall, now it is
sand and gravel at
40
0 m high
vertical spacing of 0.5 to
2m
• Reeds were also used to
form plaited ropes
approximately 100 mm
in diameter which pass
through the structure
and
d actt as reinforcement
i f
t
Geosynthetics - Introduction
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Ziggurats of Mesopotamia
((source from Reco web site))
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Great Wall of China
7th century
y BC to about 17th century
y AD
Sections in eastern China were mainly made
with bricks and chiseled stones, those in
western China were made with less durable
materials (often with clay or pounded earth
reinforced with tree branches).
Geosynthetics - Introduction
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Geosynthetics - Introduction
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Geosynthetics - Introduction
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Adobe Bricks
Adobe is derived from the
Arab word, "at-tub," referring
to the earth bricks Arabs made
as early as 7000 BC.
A man making adobe bricks in the
Draa Valley town of Tamgroute,
southern Morocco,
These early builders realised
was that if straw, which has a
good
d tensile
il strength
h was
embedded in a block of mud,
which has good compressive
strength
g and left to dry
y the
resulting brick would resist
both tearing and squeezing.
These composite bricks made
excellent building materials.
materials
Similar bricks were also manufactured by Incas and
Aztecs in American continents
Geosynthetics - Introduction
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Applications of reinforced soil in
R
Rural
l Indian
I di
constructions
t
ti
In rural India,
India mud walls are traditionally built
with bamboo mats – another fine example of
reinforced soil application from early days
Geosynthetics - Introduction
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Early applications in last century
• Corduroy mats for forest access roads in
South Carolina 1920’s
1920 s
• Filter fabrics used by Terzaghi
• Polyvinyl bags for sea walls in Japan
instead of straw bags
• Geotextile tubes for dykes in Netherlands
• Polymer meshes/membranes in Europe
Geosynthetics - Introduction
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Henri Vidal (re)invents
Reinforced Earth in 1963
The concept of
reinforced soil was
accidentally thought
about by Mr. Vidal while
playing with his children
on a beach
Henri Vidal
French Engineer &
Architect
An early form of Reinforced
Earth using steel strip
reinforcement
i f
t and
d steel
t l
membrane facing
1963 : Patent filed for
Reinforced Earth
Geosynthetics - Introduction
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Basic principle of reinforced earth
Without reinforcement
With reinforcement
Geosynthetics - Introduction
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Two identical pyramids made of dry sand with and without
reinforcement layers
Geosynthetics - Introduction
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Response of Unreinforced Soil Pyramid
Immediate collapse
under load from a
student
Close-up of foot prints
Large deformations
even under small load
Immediate collapse of unreinforced soil pyramid under
g due to lateral flow of dry
y sand
loading
Geosynthetics - Introduction
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Response of Reinforced soil pyramid
Careful initial loading on reinforced
pyramid through deadweights
Final loading by the same student
standing
t di on it – no visible
i ibl d
deformations
f
ti
!!!
Geosynthetics - Introduction
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Geotextiles or Geosynthetics ?
• Originally, most of the modern applications used
geotextiles. Hence, all products were erroneously
referred to as geotextiles.
• Even the international society was originally called
as International Geotextile Society. Name of
society changed later to International
G
Geosynthetics
th ti Society.
S i t
• Useful information can be found at website
www.geosyntheticssociety.org
• Society Membership is free for students
Geosynthetics - Introduction
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Graphical symbols proposed by IGS
letter
Symbol symbol
product
Geosynthetics - Introduction
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Letter Symbols for
Different Functions of Geosynthetics
B
D
E
F
P
R
S
Barrier (fluid)
Drainage
Surficial Erosion Control
Filtration
Protection (of geomembranes)
Reinforcement
Separation
Geosynthetics-Introduction
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Shallow unreinforced
slope
Extra road
space gained
Steep reinforced
slope
Geosynthetic reinforcement layers
Geosynthetics – Introduction
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aggregate layer
geotextile separator
subgrade
soil
Prevents the intermixing,
prevents piping, strength of
aggregate is preserved
Separation Function in a pavement layer
Geosynthetics - Introduction
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Filtration Function
Water coming out without
fine soil particles
Geotextile layer acting
as a filter
Geosynthetics - Introduction
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Surface Erosion protection
Erosion
E
i
protection
t ti
layer
Geosynthetics - Introduction
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Drainage function of a geotextile layer
ingress
g
of water into pavement
p
layers
y
flow of water
flow of water
drain
drain
Geosynthetics - Introduction
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TYPES OF GEOSYNTHETICS
•
•
•
•
•
•
•
•
Geotextiles
Geogrids
Geonets
Geomembranes
P f b i t d vertical
Pre-fabricated
ti l d
drains
i
(PVD)
Geosynthetic Clay Liner (GCL)
Geocells (3-d confinement)
Geocomposites & Geo
Geo-others
others
Geosynthetics - Introduction
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Geotextiles
• Engineered sheet like products made of
natural or synthetic materials
• Woven and non-woven types
• Used for separation, drainage, filtration,
erosion control and reinforcement
Geosynthetics - Introduction
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Woven fabric – weave
pattern
tt
is
i visible
i ibl
Non-woven
Non
woven fabric –
fibres are randomly
oriented
Rao (1995)
Two Types
yp of Geotextiles
Geosynthetics - Introduction
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Some pictures of geotextiles
Thin geotextile – used
as separator, filtration
Thick geotextile used
for cushion and
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drainage
woven
non-woven
Natural geotextiles made of jute
Geosynthetics - Introduction
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A woven g
geotextile fabric
Geosynthetics - Introduction
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Geotextile layer being applied
below railway track
Geosynthetics - Introduction
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Geogrids
• Sheet like products with open apertures. Excellent
interlocking
g with soil. High
g strength
g p
products,, used for
reinforcement.
• The geogrids are of several varieties. The extruded
grids
id h
have llow strength
h ((e.g. Netlon
N l India
I di products).
d
)
Stretched grids (e.g. Tensar products) are made by
stretching process.
process More recently several types are
made by knitting, welding process, etc.
• Uniaxial products used as reinforcement layers in
retaining walls and embankments
• Biaxial products used are used in road bases, below
rail tracks
tracks, ground reinforcement
Geosynthetics - Introduction
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Geogrids manufactured by stretching process
Orientation of p
polymers
y
in p
preferential directions
Geosynthetics - Introduction
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St t h d uniaxial
Stretched
i i l geogrid
id
Knitted polyester geogrids
Geosynthetics - Introduction
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Geogrids used at at Hindustan Zink Limited,
Visakhapatnam
Geosynthetics - Introduction
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Geogrid reinforcement in pavements
Geosynthetics - Introduction
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Innovative use of geogrids for shore protection at Navi Mumbai
Geosynthetics - Introduction
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