lecture 3 geosynthetic properties and test...
TRANSCRIPT
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27-03-2020 NIT JAMSHEDPUR 1
UNIT-V
Subject: Ground Improvement (CE610)
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A planar product manufactured from polymeric
material used with soil, rock, earth, or other
geotechnical engineering related materials as an
integral part of a man-made project, structure, or
system
Geosynthetics ?
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Types of Geosynthetics
Geotextiles
Geogrids
Geonets
Geomembranes
Geosynthetic clay liners
Geopipes
Geocomposites 3/27/2020 NIT Jamshedpur 3
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They are indeed textiles in the traditional sense,
but consist of synthetic fibers rather than natural
ones such as cotton, wool or silk.
Thus biodegradation is not a problem
They are made into a flexible, porous fabric by
standard weaving machinery or are matted
together in a random, or nonwoven, manner
Geotextile ?
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Woven Geotextiles: high tensile strength, modulus and low elongation
Non-woven Geotextiles: high permeability because of their high elongation
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Separation
Reinforcement
Filtration
Functions of geotextile
Drainage
Liquid barrier
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Separation
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Reinforcement
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Drainage and Filtration
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Determine critical function Filtration,
Reinforcement, Separation or Drainage
If Filtration → FOS
If Reinforcement → Tensile strength and Modulus
If Separation → Survivability
Consider long-term performance
Design Considerations
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Geogrids are plastics formed into a very open, gridlike
configuration i.e. they have large apertures
Used primarily as reinforcement of unstable soil and
waste masses
It is differ from geotextile, as geogrid facilitate
interlocking of soil/aggregate particle within their
opening.
Geogrids ?
Biaxial Geogrid Uniaxial Geogrid Woven or Welded Geogrid 3/27/2020 NIT Jamshedpur 11
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Application 3/27/2020 NIT Jamshedpur 12
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Design Considerations
Consider tensile modulus and strength
Mechanical interlock with granular fills
Damage during construction
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Reinforcement mechanism
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Their design function is completely within the drainage area
where they have been used to convey fluids of all types
Though they are used for the drainage function but they have
high tensile strength
Generally used along with one or two geotextile matter one at
the top and other at the bottom to prevent soil intrusion
Design Considerations: flow rate (which is preferred to
transmissivity), Normal stress, Hydraulic gradient
Geonets ?
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Geomembranes ?
The materials themselves are "impervious" thin sheets of
rubber or plastic material used primarily for linings and
covers of liquid- or solid-storage or disposal facilities
Thus the primary function is always as a liquid or vapor
barrier
Design Considerations: Leakage rates, potential slip-surface on
slopes, exposure to long-term environmental agents of
weathering (sunlight, air, burrowing rodents
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Seepage barrier
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Geosynthetic Clay Liners (GCLs) ?
Geosynthetic Clay Liners (or GCLs) are the newest
subset within Geosynthetic materials
They are rolls of factory fabricated thin layers of
bentonite clay sandwiched between two Geotextiles or
bonded to a Geomembrane
The engineering function of a GCL is containment as a
hydraulic barrier to water, leachate or other liquids and
sometimes gases
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Cross-section sketches of GCL 3/27/2020 NIT Jamshedpur 20
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A Geocomposite consists of a combination of
Geotextile and Geogrid; or Geogrid and
Geomembrane; or Geotextile, Geogrid, and
Geomembrane; or any one of these three materials
with another material (e.g., various soils, deformed
plastic sheets, steel cables, or steel anchors)
The major functions encompass the entire range of
functions listed for Geosynthetics discussed
previously: separation, reinforcement, filtration,
drainage, and liquid/vapor barrier
Geocomposite ?
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Geocomposite 3/27/2020 NIT Jamshedpur 22
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Applicat ions
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Determine the function of the Geosynthetic component
in question
Determine the required properties (filtration size, in-
plane or cross-plane hydraulic flow capacity, required
tensile strength and modulus)
In specifications, reference required material
properties to the standard “INDEX” tests such as
Strength (tensile, burst, tear), Filtration (FOS),
Permeability and Drainage capacity
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Summary
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Geosynthetic properties and test methods
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Properties of geosynthetics:
Physical properties
Mechanical properties
Hydraulic properties
Endurance properties
Firstly for any project the design engineers must check
the required specifications of geosynthetic materials.
Without knowing proper specifications, it is very
difficult to select the correct geosynthetic for any
specific project.
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Mass per unit area (Weight)
Thickness
Specific gravity
Stiffness or flexural rigidity or flexural stiffness
Physical Properties:
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Mass per unit area (ASTM D5261)
Five test specimens are to be weighed in a weighing
machine (accuracy of 0.01 g) and average value is
recorded.
Test samples are of size 100 mm × 100 mm
Unit is expressed as g/m2
The cost of geotextile is directly related to the weight of
geotextile .
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Thickness (ASTM D5199)
according to
Geotextiles exhibit different thickness different
pressures.
The thickness is measured to an accuracy of 0.02
mm under a specified pressure of 2.0 kPa.
Sample size is 200 mm × 200 mm. The thickness is
generally in the range of 0.25 to 8.5 mm.
The thickness of geogrids and geomembranes are
measured under a normal stress of 20 kPa.
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Thickness measurement of geotextile
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Materials Sp. Gravity
Polypropylene (PP) 0.91
Polyethylene (PE) 0.9 to 0.96
Polyester (PET) 1.22 to 1.38
Polyvinyl chloride (PVC) 1.69
Nylon 1.05 to 1.14
Specific gravity (ASTM D 792 or D1505)
Specific gravity can be defined as ratio of the unit
weight of material to the unit weight of distilled
water at 4°C.
Specific gravity of different geosynthetic materials
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The geotextile specimen is a 25 mm wide strip.
The geotextile is placed along the length of a horizontal
plane and bends gravitationally under its own weight on
a inclined plane making an angle of 41.5 degree with
the horizontal.
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Stiffness or flexural rigidity or flexural stiffness
(ASTM D1388)
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Stiffness of the geotextile = (l/2)3 x w
l = length of overhang geotextile and bending length
= l/2 (cm), w = mass per unit area (mg/cm2)
The unit of stiffness is mg-cm.
The minimum stiffness of geotextile depends on the
various degree of required workability (Haliburton
et al., 1980)
The property is important in field workability
requirements for installation of geotextile.
If the soil is very poor or California bearing ratio
value is very less, the stiffness of geotextile required
is very high.
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Mechanical Properties
Compressibility
Tensile strength test of geosynthetics
Burst strength test
Puncture Resistance Test
Penetration resistance test (drop test)/ drop cone
(impact strength)/ tear (impact) resistance
Tensile behavior of geogrid
Tensile strength of Gabions
Direct shear test
Pullout or anchorage resistance
Tensile strength of geomembrane
Tear resistance of Geomembrane
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Compressibility
Compressibility indicates the reduction in thickness under
applied pressure. Compressibility of geotextile depends on its
thickness and mass per unit area.
As the pressure increases, thickness of non-woven needle-
punched (NW-NP) and resin bonded geotextiles gets reduced
significantly and accordingly, the transmissivity gets
reduced.
Compressibility of woven and non-woven heat bonded
geotextile (NW-HB) is low.
Compressibility of nonwoven needle-punched geotextile
plays a very important role as most of the time we use these
type of geotextiles to pass the liquid along their plane. 3/27/2020 NIT Jamshedpur 34
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Variation in thickness of geosynthetics with change in
pressure
It is clearly observed that nonwoven needle punched
geosynthetics are more compressible. 3/27/2020 NIT Jamshedpur 35
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Tensile strength
Wide width tensile strength (ASTM D4595 and ISO 10319)
Very wide width tensile strength test
Narrow strip tensile strength (ASTM D4751)
Sewn seam strength of geotextile
(ASTM D4884 and ISO 13426)
Grab tensile strength (ASTM D4632)
Trapezoidal tear strength test
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Wide width tensile strength (ASTM D4595)
Nonwoven geotextiles Woven jute geotextiles
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The machine strain rate is 10 ± 3 %.
The reason for the necessity of wide-width specimens is that
geotextiles (particularly non-woven) achieve high poison’s
ratio value from narrow strip test.
Tensile strength of geotextile (Tgeotextile) can be expressed
as force per unit width of geotextile.
Fb/ W (kN/m) Fb = Observed breaking force (kN),
and W = Specimen width (meter)
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Size of sample for very wide width test
Very wide width tensile strength test
For design purpose, the very wide width tensile test is not
recommended.
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Narrow strip tensile strength (ASTM D 1682)
Strain rate = 300 mm/ min
Tensile strength appears
low compared to wide width
tensile strength test.
Not recommended as design
value.
Size of test sample with the
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Tensile modulus:
Different tensile modulus from typical stress-strain curves
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Tensile strength vs. strain curves for different geotextiles
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Sewn seam strength of geotextile
(ASTM D4884 and ISO 13426)
(After Diaz, 1985)
Size of test sample for sewn seam
strength
Strain rate =10 ± 3 %/ min, Unit in kN/m
Butterfly seam is recommended for sewing 3/27/2020 NIT Jamshedpur 43
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Main strong reasons for exploring this exciting
new engineering construction material in civil
engineering are as follows:
Excellent stress-strain behavior
Good flexibility
Excellent filtration characteristics
High water permeability
Excellent mechanical properties
Can be welded together
Does not form by-products
High resistance to climate condition
High resistance to chemical and biological attack
Chemically ultraviolet stabilized
Time, cost, rapid construction, environment friendly,
sustainability and durability
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Mechanisms of reinforced soil structures
Region A & C, direct shear
tests can be employed to
quantify soil–reinforcement
bond.
Region B, plane strain test
similar to the in-soil tensile
test can be used.
Region D, pull-out tests
would be applicable.
Interaction mechanisms in a geosynthetic
reinforced soil wall (Marques and Palmeira 2009)
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Load Carrying Mechanism:
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https://www.youtube.com/watch?v=0olpSN6_TCc
https://www.youtube.com/watch?v=1RuGFtK_Ars
https://www.youtube.com/watch?v=UZq-wAAu918