Geosynthetics

GEOSYNTHETICS
1
ANIRUDHAN K M
LECTURER IN CIVIL ENGINEERING

Geosynthetics
• A planar product manufactured from
polymeric material used with soil, rock, earth,
or other geotechnical engineering related
material as an integral part of a man-made
project, structure, or system.
2

Types of Geosynthetics
• Geotextiles
• Geogrids
• Geonets
• Geomembranes
• Geosynthetic clay liners
• Geocells/geo web members
• GeoPipes
• Geofoam
• Geocomposites
3

GeoTextiles
• Flexible, textile-like fabrics of controlled
permeability
• Continuous sheets of woven, nonwoven,
knitted or stitch-bonded fibres or yarns.
• The sheets are flexible and permeable and
generally have the appearance of a fabric.
• Geotextiles are used for separation, filtration,
drainage, reinforcement and erosion control
applications.
• Used in soil, rock and waste materials
5

GeoTextiles
• Woven geotextile:
– Produced by interlacing,
usually at right angles, two or
more sets of yarns (made of
one or several fibres) or
other elements using a
conventional weaving
process with a weaving loom.
• Nonwoven geotextile
– A geotextile produced from
directionally or randomly
oriented fibres into a loose
web by bonding with partial
melting, needle-punching, or
chemical binding agents
(glue, rubber, latex, cellulose
derivative, etc.).
6

GeoTextiles
• Knitted geotextile
– Produced by inter-
looping one or more
yarns (or other
elements) together
with a knitting
machine, instead of a
weaving loom.
• Stitched geotextile
– A geotextile in which
fibres or yarns or both
are
interlocked/bonded by
stitching or sewing. 7

GeoTextiles
• (L) woven monofilament
• (R) calendered woven
monofilament
• (L) woven multifilament
• (R) woven slit film
• (L) nonwoven needle-
punched
• (R) nonwoven heat-
bonded
8

GeoGrids
• Stiff or flexible polymer grid-like sheets with
large apertures
• Used primarily as reinforcement of unstable
soil and waste masses
• Geogrids are either stretched in one or two
directions or made on weaving machinery by
unique methods.
10

GeoGrids
extruded – (i) uniaxial (ii) biaxial;
(b) Bonded (c) woven. 11

GeoGrids
• Uniaxial geogrid
– Produced by the longitudinal stretching of a regularlypunched
polymer sheet
– Possesses a much higher tensile strength in the longitudinal
direction than the tensile strength in the transverse direction.
• Biaxial geogrid
– Produced by stretching in both the longitudinal and the
transverse directions of a regularly punched polymer sheet
– Possesses equal tensile strength in both the longitudinal and
the transverse directions.
12

GeoNets
• Stiff polymer net-like sheets with in-plane
openings
• Used primarily as a drainage material within
landfills or in soil and rock masses
• Formed by two sets of coarse, parallel,
extruded polymeric strands intersecting at a
constant acute angle.
• Rhombus Shaped Apertures
• The network forms a sheet with in-plane
porosity
• Functions to perform the in-plane drainage of
liquids or gases 13

GeoMembranes
• Used as barriers for liquid or solid waste
containment
• Planar - Relatively impermeable, synthetic sheet
• manufactured from materials of low permeability
to control fluid migration in a project as a barrier
or liner
• The materials may be polymeric or asphaltic or a
combination thereof.
• The term barrier applies when the geomembrane
is used inside an earth mass.
• The term liner is usually reserved for the cases
where the geomembrane is used as an interface
or a surface revetment. 16

Geosynthetic Clay Liners
• Prefabricated bentonite clay layers incorporated between
geotextiles and/or geomembranes
• A geosynthetic clay liner is a manufactured hydraulic barrier
• Used as alternative material to substitute a conventional
compacted soil layer
• For the low-permeability soil component of various
environmental and hydraulic projects including landfill and
remediation projects
• It consists of a thin layer of sodium or calcium bentonite (mass
per unit area ≈ 5 kg/m2)
• Bentonite sandwiched between two sheets of woven or
nonwoven geotextiles or mixed with an adhesive and
attached to a geomembrane.
• The sodium bentonite has a lower hydraulic conductivity.
19

GeoCells
• Relatively thick, three-dimensional networks
constructed from strips of polymeric sheet.
• The strips are joined together to form
interconnected cells that are infilled with
• In some cases 0.5 m to 1 m wide strips of
polyolefin geogrids have been linked together
with vertical polymeric rods used to form
deep geocell layers called geomattresses.
21

GeoPipes
• Perforated or solid wall
polymeric pipes
• Used for the drainage of
various liquids
• Plastic pipe (smooth or
corrugated with or
without perforations)
placed beneath the
ground surface and
subsequently backfilled
25

GeoFoams
• Geofoam blocks or slabs are created by
expansion of polystyrene foam
• Low-density network of closed, gas-filled cells.
• Used for thermal insulation, as a lightweight fill
or as a compressible vertical layer to reduce earth
pressures against rigid walls.
• Manufactured by the application of the polymer
in semi-liquid form through the use of a foaming
agent
• Lightweight material in slab or block form with
high void content
• Usage as lightweight fills, thermal insulators and
drainage channels. 26

GeoComposites
• Hybrid systems of any of the different
geosynthetic types
• Which can function as specifically designed for
use in soil, rock, waste and liquid related
problems
27

Functions of Geosynthetics
• Separation - Prevent the mixing of two different soils or materials (using
geotextiles, geocomposites)
• Reinforcement - Provide tensile forces in the soil (using geogrids, and
geotextiles)
• Confinement - Restrain the lateral movement of a soil mass geocells
• Filtration - Allow the passage of fluids preventing the migration of soil
particles(geotextiles, geocomposites)
• Drainage - Transport of fluids (geonets, geocomposites)
• Barrier or Containment - Fluid barrier (using Geomembranes,
geocomposites)
• Erosion Control - Avoid the detachment and transport of soil particles by
rain, runoff and wind; root anchorage using geomats, geocells, biomats,
bionets
• Protection - Avoid damages to a structure, a material or another
geosynthetic (using nonwoven geotextiles, geonets, geocomposites)
29

• Separation
– Prevention of intermixing of adjacent dissimilar soils and/or fill materials during
construction and over a projected service lifetime
– Provided at the soil subgrade level in pavements or railway tracks to prevent
pumping of soil fines into the granular subbase/base course and/or to prevent
intrusion of granular particles into soil subgrade.
Basic mechanism involved in the separation function: (a) granular fill–soft soil system
without the geosynthetic separator; (b) granular fill–soft soil system with the geosynthetic
separator.
30

• Reinforcement
– A geosynthetic performs the reinforcement function by improving the
mechanical properties of a soil mass as a result of its inclusion.
– Reinforced soil posses high compressive and tensile strength (and similar, in
principle, to the reinforced concrete)
31

• Filtration
– A geosynthetic may function as a filter that allows for adequate fluid flow with
limited migration of soil particles across its plane over a projected service
lifetime.
– When a geosynthetic filter is placed adjacent to a base soil (the soil to be
filtered), a discontinuity arises between the original soil structure and the
structure of the geosynthetic.
– This discontinuity allows some soil particles, particularly particles closest to the
geosynthetic filter and having diameters smaller than the filter opening size
32

• Drainage
– If a geosynthetic allows for adequate fluid flow with limited migration of soil
particles within its plane from surrounding soil mass to various outlets
33

• Barrier
– A geosynthetic performs the fluid barrier function, if it acts like an
almost impermeable membrane to prevent the migration of
liquids or gases over a projected service lifetime
34

• Barrier
35

• Erosion Control
– A geosynthetic provides surface stabilization when it is placed on a soil surface
to restrict movement and prevent dispersion of surface soil particles subjected
to erosion actions of rain and wind, often while allowing or promoting growth
of vegetation.
– A geosynthetic provides vegetative reinforcement and controls erosion of Soil
36

• Protection
– A geosynthetic, placed between two materials, performs the
protection function when it alleviates or distributes stresses and
strains transmitted to the material to be protected against any
damage
37

Applications
Geosynthetics in Walls
48

Applications
Geosynthetics in Waste Water Treatment 49

Properties of Geosynthetics
• Physical Properties
– Specific gravity
– Unit mass (weight)
– Thickness
– Stiffness
Some more physical properties which are important for
geogrids and geonets
– Type of structure
– Junction type
– Aperture size and shape
– Rib dimensions
– Planar angles made by intersecting ribs and vertical angles
made at the junction point.
The physical properties are more dependent on temperature
and humidity
50

• Determined by the displacement
method.
• In case of geomembranes, a
known mass is weighed in air and
then in water.
• Given by the ratio of its weight in
air to the difference between its
weight in air and in water.
• Specific gravity is widely used in
geomembrane identification and
quality control 51

52

– Mass per Unit Area
• Usually given in units of gram per square metre (g/m2)
• It is determined by weighing square or circular test
specimens of known dimensions (generally area not less
than 100 cm2).
• Linear dimensions should be measured without any
tension in the specimen.
• For commonly used geo-synthetics, it varies in order of
100 to 1000 g/m2.
• Unit weight of geo-textiles< Unit weight of
geomembranes may have substantially larger values of
mass per unit area, even up to several thousands grams
per square metre.
• It should be measured to the accuracy nearest to 0.01 %
of total specimen weight.
• Fabric cost is directly related to mass per unit area (Unit
weight).
• Important for Economy of a project.
Codes Used
•ASTM D5261-92
(Reapproved 1996)
•ASTM D5993-99
•ASTM D6566-00
•BS EN 965-1995
•CAN/CGSB 148.1 No. 2-
M85
•IS 14716-1999
•ISO 9864-1990
53

– Thickness
• The thickness of a geosynthetic is
the distance between its upper and
lower surfaces, measured normal
to the surfaces at a specified
normal compressive stress.
• Generally 2.0 kPa for geotextiles
and 20 kPa for geogrids and
geomembranes.
• Measured to the accuracy of
0.02mm
• Thickness varies in between
0.25mm to 7.5mm
• Thickness is important for
permittivity (c/s plane)and
Transmissivity (in-plane)
Codes Used
•ASTM D5199-01
•ASTM D5994-98
•ASTM D6525-00
•CAN/CGSB 148.1 No. 3-
M85
•BS EN 964 (Part 1)-1995
•IS 13162 (Part 3)-1992
•ISO 9863 (Part 2)-1996
54

–Stiffness
• It is ability to resist flexure (bending)
under its own weight
• It can be measured by its capacity to
form a cantilever beam without
exceeding a certain amount of
downward bending under its own
weight.
• The stiffness of a geosynthetic
indicates the feasibility of providing a
suitable working surface for
installation.
Codes Used
•CAN/CGSB 148.1 No. 2-M85
•IS 14716-1999
•ISO 9864-1990
55

• Mechanical Properties
– Compressibility
– Tensile strength
56

– Compressibility
• Is very important for nonwoven geotextiles, because
they are often used to convey liquid within the plane of
their structure.
• Compressibility can be studied by applying compressive
stress, by placing the geosynthetic between two plates
and constant stress applied.
57

– Tensile strength
• Determination
– Tensile test on a 200-mm wide geosynthetic strip with a gauge length of 100
mm.
– Entire width of a 200-mm wide geosynthetic specimen is gripped in the jaws
of a tensile strength testing machine and it is stretched in one direction at a
prescribed constant rate of extension until the specimen ruptures (breaks).
58

• Endurance Properties
– Creep
– Durability
– Abrasion
– Long Term Flow Characteristics
59

– Creep
• Creep is the time-dependent increase in accumulative strain
or elongation in a geosynthetic resulting from an applied
constant load.
• Test for determining the creep behaviour of a geosynthetic.
• 200 mm wide specimen.
• Load applied using weights, or mechanical, hydraulic or
pneumatic systems.
• Test duration : 100 h.
• For a full analysis of creep properties, durations of 10,000 h
will be necessary.
60

– Durability
• The durability of a geosynthetic may be regarded as its
ability to maintain requisite properties against
environmental or other influences over the selected
design life.
61

– Abrasion
• Abrasion of a geosynthetic is defined as the wearing
away of any part of it by rubbing against a stationary
platform by an abradant with specified surface
characteristics.
• The ability of a geosynthetic to resist wear due to
friction or rubbing is called abrasion resistance.
62

– Long Term Flow Characteristics
• The compatibility between the pore size openings of a geotextile
and retained soil particles in filtration and/or drainage applications
can be assessed by the gradient ratio test.
• This test is basically used to evaluate the clogging resistance of
geotextiles with cohesionless soils (having a hydraulic
conductivity/permeability greater than 5 x10-4 m/s) under
unidirectional flow conditions.
63

• Survivability Properties
– Tearing strength
– Static puncture strength
– Impact strength (dynamic puncture strength)
– Bursting strength
– Fatigue strength
– Friction Behaviour
64

– Tearing strength
• The ability of a geosynthetic to withstand
stresses causing to continue or propagate a
tear in it, often generated during their
installation.
• The tearing strength of geotextiles under
in-plane loading is determined by trapezoid
tearing strength test.
65

– Static puncture strength
66

– Impact strength (dynamic puncture strength)
67

– Bursting strength
• Common test called as Mullen burst test.
68

– Fatigue strength
• Specimen is stressed longitudinally at constant rate of extension to a
predetermined load (less then failure load) and then back to lower zero
load.
• This cycling is repeated until failure occurs.
• ower stress failure --- Larger number of cycles required.
• Examples: seismic load, rail road loadings, wave and tidal action.
69

– Friction Behavior
• It is important that the bond developed between the
soil and the geosynthetic is sufficient to stop the soil
from sliding over the geosynthetic or the geosynthetic
from pulling out of the soil when the tensile load is
mobilized in the geosynthetic.
Direct Shear Test Pull Out Test
70

• Hydraulic Properties
– Porosity
– Permittivity
– Transmissivity
• The voids (or holes) in a geosynthetic are called pores or
openings.
• The measurement of sizes of pores and the study of
their distribution is known as porometry.
71

– Porosity
72

– Permittivity
• Cross Plane Permeability
Typical test arrangements of constant head in-plane water flow apparatus: (a) full
width flow; (b) radial flow. 73

– Transmissivity
• In Plane Permeability
74

Reinforced Earth
• A geosynthetic performs the reinforcement function by improving
the mechanical properties of a soil mass as a result of its inclusion.
• When soil and geosynthetic reinforcement are combined, a
composite material, ‘Reinforced Soil’, possessing high compressive
and tensile strength (and similar, in principle, to the reinforced
concrete) is produced.
• In fact, any geosynthetic applied as reinforcement has the main task
of resisting applied stresses or preventing inadmissible
deformations in geotechnical structures.
• In this process, the geosynthetic acts as a tensioned member
coupled to the soil/fill material by friction, adhesion, interlocking or
confinement and thus maintains the stability of the soil mass
76

Reinforcing Elements
• The reinforcing elements (strip, grid or sheet,
fabricated from metals or geosynthetics)
• Facing units to prevent the soil from erosion
(Pre-cast concrete panels, metal sheets and
plates, gabions, welded wire mesh, shotcrete,
wrapped sheets of geosynthetics)
• Backfill materials (local soils, specified soils,
marginal materials)
78

Structures with Vertical Faces
82

83

84

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