Testing of Geosynthetics-3-L8nptel.ac.in/courses/105106052/downloads/Lecture-8.pdf · Geonets are predominantly used for erosion control works orGeonets are predominantly used for

Testing of Testing of Geosynthetics

…… continued

Prof K. RajagopalDepartment of Civil EngineeringDepartment of Civil Engineering

IIT Madras, Chennaie mail: gopalkr@iitm ac ine-mail: [email protected]

Recap

Earlier lectures have discussed the testing for the following properties of geotextilesfor the following properties of geotextiles

Physical .. Fundamental material properties, e.g. specific gravity, etc.p p , g p g y,

Mechanical – strength propertiesHydraulic – permeability propertiesHydraulic permeability properties

Testing of Geosynthetics-3 2/36

Other Properties of Geotextiles

• Abrasion resistance• Durability propertiesDurability properties• Melt flow index• Asphalt retention• Asphalt retention


Abrasion Resistance ASTM D1175 Abrasion is the “wearing away of a part of the material due to

rubbing against another surface” Degradation in strength and material loss may happen due to

ti bbi ith h d h d f d i icontinuous rubbing with rough and hard surfaces during service life of a geotextile.

Abrasion is especially important in below railway track applications Rotary platform with a double head fitted with 1000 g vitrified Rotary platform with a double head fitted with 1000 g vitrified

abrasion wheels is used in this test. Geotextile is a disk shaped sample with 90 mm outer diameter and 60 mm inner diameter.

After 1000 cycles of rotation, strip tensile strength tests are After 1000 cycles of rotation, strip tensile strength tests are performed

Abrasion resistance is expressed as the ratio of the tensile strength of the abraded sample with that of the virgin sample.

Typical loss of tensile strength is about 40% after 1000 abrasion cycles.

Loss in weight is also reported after the abrasion tests


Abrasion by sand paper (ASTM D4886)• The abrasion in this test is induced by rubbing a linear geotextile sample by a sand paper

• Loss in weight and tensile strength after 750 abrasion cycles is reported as the abrasion y ploss.

Schematic of an abrasion testing device


abrasion testing device

Durability tests on geotextiles

Accelerated Durability Studies on Geotextiles

Wetting of samples in seawater Drying of samples in sun lightd i d ti


during nights during day time

Results from alternate wetting and dryingResults from alternate wetting and dryingWOVEN G/T(WHITE) WOVEN G/T(BLACK)

GEOCOMPOSITE NON WOVEN

300

350

/m)

GEOCOMPOSITE NON‐WOVEN

200

250

ENGTH

(kN/

50

100

150

ENSILE STR

E

0

50

0 20 40 60 80 100

TE


TIME (DAYS) – No. of cycles

Tests on paver or overlay fabricsTests on paver or overlay fabrics

• Paver or overlay fabrics are used in surfacePaver or overlay fabrics are used in surface treatment of pavements for protection of surface

• Prevents the propagation of cracks from old• Prevents the propagation of cracks from old pavement section to the new overlay section


Use of overlay fabrics for protecting pavementsUse of overlay fabrics for protecting pavements

9/36Testing of Geosynthetics-3

P t f ith l f b iPavement surface with overlay fabric

Typical alligator cracks on the pavement surface

Pavement surface without overlay fabric

Performance of asphalt pavements with and without overlay fabrics

10/36Testing of Geosynthetics-3

Cyclic load tests to study the propagation of reflected cracks


Typical results from laboratory tests on influence of geosyntheticlayer on reflection cracking (Khodaii et al 2009)


layer on reflection cracking (Khodaii et al. 2009)

Melting point of paving fabrics

o When geosynthetics are used in flexible pavements they come in contact with hot asphalt during y gconstruction.

o Geotextiles should not undergo structural changes due to exposure to excessive heat during construction.

o The temperature at which the fibres melt can be determined from this test.Diff ti l S i C l i t (DSC) b do Differential Scanning Calorimeter (DSC) can be used to determine the melting point of the polymer as thermal transition pointthermal transition point.


Asphalt retention of paving fabrics(ASTM D6140)(ASTM D6140)

This test determines how well the geotextile can bond with h ltasphalt

Geotextile samples of 100 × 200 mm size are takenThey are submerged in bitumen at 1352C for 30 minutesThey are submerged in bitumen at 1352 C for 30 minutesThe saturated specimens are hung in the same oven at the

same temperature for 30 minutes from one end and for another 30 minutes from another end

Then the test specimens are cooled for 30 minutes and weighed to the nearest 0 1gweighed to the nearest 0.1g.

Asphalt retention = (Wsat – Wo) /Ag where Wsat is the saturated weight of the sample (g), Wo is original weight of the sample g (g) o g g(g) and Ag is the area of the sample in m2.


Tests on Geogrids

• Aperture opening & Percent Open Areap p g p• Thickness of rib and juctions• Number of ribs per meter lengthp g• Mass per Unit Area• Tensile strength• Interface frictional strength

• Shearll t• pullout

• Connection strength between facing blocks and geogridsblocks and geogrids


Biaxial composite geogridnodes

nodesApertureAperture

opening sizesbars

ribs


Uniaxial geogrid

btransverse bars

ribs

Elongated apertures with very long ribs and short bars


Elongated apertures with very long ribs and short bars

Thickness & No. of ribs and bars per unit length

• Thickness of barsThickness of bars

• Thickness of ribs

hi k f d• Thickness of nodes

• Count the no. of ribs and bars per metrelength by spreading the geogrid on a flat surface


Percent Open Area• Samples of at least 200 mm × 250 mm

representative of the geogrid are cut from the rollrepresentative of the geogrid are cut from the roll• The geogrid pattern is drawn on a piece of paper• Weigh the paper with the grid pattern accurate to• Weigh the paper with the grid pattern accurate to

0.001 g• Cut out the grid opening areas from the paper• Cut out the grid opening areas from the paper• Weigh the cut out portions• Percent Open Area is the ratio of the weight of the• Percent Open Area is the ratio of the weight of the

cut out portions to the total weight of the paper multiplied by 100.


multiplied by 100.

Mass per Unit area

Same procedure as used for geotextiles is

Mass per Unit area

Same procedure as used for geotextiles isapplicable for the Mass per Unit Area ofthe geogrids also The value isthe geogrids also. The value isexpressed in units of g/m2.


Tensile Strength of Geogrids

• ASTM D4595 (minimum width of 200 mm and

Tensile Strength of Geogrids

ASTM D4595 (minimum width of 200 mm and gauge length of 100 mm, etc.)

• ASTM D6637 (single rib or multi ribs)• ASTM D6637 (single rib or multi‐ribs)

• Loading of samples at strain rate of 103% i istrain per minute

• Load at different deformations is measured to plot a graph between the strain on x‐axis and load/m on y‐axis


ASTM D6637ASTM D6637

Three junctions or 300 mm lengthg

M th d A i i l ib t ti


Method A using single rib testing

Three junctions or 300 mm length

Method-B using multi-ribs testing


Method B using multi ribs testing

extensometer

Gauge length for gstrains

Fixed clamps Roller clamps


Different types of grips

Roller gripsSpacer block

Special grips used for testing extruded geogrids– grid is held in position d t th l t ddue to the elongated nodes – width of the spacer blocks is changed for different geogrids


for different geogridsTrapezoidal grips

Tensile Strength Test of a knitted geogrid using roller clamps as per Method-A single rib test - geotextile padding


given at supports to promote rupturewithin the gauge length

Tensile strength

• Tensile strength of geogrid per meter width

Tensile strength

Tensile strength of geogrid per meter width

= Peak tensile load x No. of ribs per meter width/No. of ribs in the test


Installation Damage of Geogrids(ASTM D 5818)(ASTM D 5818)

Geogrids undergo damage during the construction The amount of damage depends on the type of aggregate level The amount of damage depends on the type of aggregate, level

of compaction, type of compaction equipment and construction practices

The installation damage factor is specified after extensile field tests for site specific conditions

ASTM 5818 recommends that the results from at least 20 tests should be used to determine the installation damage factor

Typical damage factors are: • for use in gravel/aggregate=1 1 to 1 2• for use in gravel/aggregate=1.1 to 1.2• for use in fine soils 1.05 to 1.1• for railway track applications, the damage factor could be much higher

because of the large angular particles


g g p


Field tests to determine the installation damage factor

Testing of Geosynthetics-3 30/36Field tests to determine the installation damage factor

Tests on Geonets & Other drainage Products

Geonets are predominantly used for erosion control works or Geonets are predominantly used for erosion control works or for drainage purposes

The in plane permeability of the geonets is evaluated using the procedure as applicable to geotextilesprocedure as applicable to geotextiles

The normal pressures should correspond to the expected normal pressures in the construction


Tests on Geomembranes

ThicknessThicknessDensityTensile strength/elongationg gPermeabilityPeel tests on seamsShShear tests on seams


Thi k f G bThickness of a Geomembrane(ASTM D5199)

Size of geomembrane sample is minimum 75 mm diameter Applied pressure is 20 kPa on a footer plate of diameter

6.35 mm For thick or stiff geomembranes, higher pressures as much

as 200 kPa may be usedy For textured geomembranes, the thickness is measured

between the projections


D it f G b Density of Geomembranes (ASTM D792)

Density of geomembranes is determined as y gapplicable for plastic materials using weights to sink them in water as per ASTM D792.


double welded seam

Direction of loads for the shear strength of a seam

seam

Direction of loads for the peel strength of a seam

Determining the Shear and Peel strengths of a seam


Determining the Shear and Peel strengths of a seam

Tensile strength and elongation at break of geomembranes (ASTM D638)

• Geomembranes are subject to

g ( )

jsevere strains during their service life due to heat from the atmosphere and also the heat produced by theand also the heat produced by the decay of waste products in landfills

Th h ld b bl t l t t• They should be able to elongate to more than 500% without rupturing

• Dumbbell shaped are cut from pgeomembrane sheets using sharp dies


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Testing of Geosynthetics-3-L8nptel.ac.in/courses/105106052/downloads/Lecture-8.pdf · Geonets are predominantly used for erosion control works orGeonets are predominantly used for