Lecture 3 Geosynthetic properties and test methodsnitjsr.ac.in/course_assignment/CE35CE610Ground... · 2020. 3. 27. · (ASTM D4884 and ISO 13426) (After Diaz, 1985) Size of test

27-03-2020 NIT JAMSHEDPUR 1

UNIT-V

Subject: Ground Improvement (CE610)

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 ?

3/27/2020 NIT Jamshedpur 2

Types of Geosynthetics

Geotextiles

Geogrids

Geonets

Geomembranes

Geosynthetic clay liners

Geopipes

Geocomposites 3/27/2020 NIT Jamshedpur 3

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 ?


Woven Geotextiles: high tensile strength, modulus and low elongation

Non-woven Geotextiles: high permeability because of their high elongation


Separation

Reinforcement

Filtration

Functions of geotextile

Drainage

Liquid barrier


Separation


Reinforcement


Drainage and Filtration


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


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

Application 3/27/2020 NIT Jamshedpur 12

Design Considerations

Consider tensile modulus and strength

Mechanical interlock with granular fills

Damage during construction


Reinforcement mechanism



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 ?


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


Seepage barrier


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


https://en.wikipedia.org/wiki/Leachate

Cross-section sketches of GCL 3/27/2020 NIT Jamshedpur 20

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 ?


Geocomposite 3/27/2020 NIT Jamshedpur 22


Applicat ions

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


Summary

Geosynthetic properties and test methods


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.

Mass per unit area (Weight)

Thickness

Specific gravity

Stiffness or flexural rigidity or flexural stiffness

Physical Properties:

NIT Jamshedpur 3/27/2020 26

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 .


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.


Thickness measurement of geotextile


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


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.


Stiffness or flexural rigidity or flexural stiffness

(ASTM D1388)

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.


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


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

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

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


Wide width tensile strength (ASTM D4595)

Nonwoven geotextiles Woven jute geotextiles

Test result on a thermally bonded nonwoven geotextile 3/27/2020 NIT Jamshedpur 37

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)


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.


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

test assembly 3/27/2020 NIT Jamshedpur 40

Tensile modulus:

Different tensile modulus from typical stress-strain curves


Tensile strength vs. strain curves for different geotextiles


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

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


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)

03/07/2012 45


Load Carrying Mechanism:


https://www.youtube.com/watch?v=0olpSN6_TCc

https://www.youtube.com/watch?v=1RuGFtK_Ars

https://www.youtube.com/watch?v=UZq-wAAu918

https://www.youtube.com/watch?v=0olpSN6_TCc

https://www.youtube.com/watch?v=1RuGFtK_Ars




Documents

Lecture 3 Geosynthetic properties and test methodsnitjsr.ac.in/course_assignment/CE35CE610Ground... · 2020. 3. 27. · (ASTM D4884 and ISO 13426) (After Diaz, 1985) Size of test