Testing of Geosynthetics

Testing of Geosynthetics

continued….. continued

Prof K. RajagopalDepartment of Civil Engineeringg g

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

Recap of earlier lectureRecap of earlier lecture

• Physical properties ‐ fundamental materialPhysical properties fundamental material properties e.g. specific gravity, mass per unit area etcarea, etc.

• Mechanical properties – strength properties e g tensile strength punching strength etce.g. tensile strength, punching strength, etc.

Testing of Geosynthetics - 2 2/30

Hydraulic Properties of GeotextilesHydraulic Properties of Geotextiles

• Apparent Opening SizeApparent Opening Size

• Cross‐plane permeability

l bili• In plane permeability

• Gradient ratio

• Long term permeability


Apparent Opening Size (ASTM D4751)Apparent Opening Size (ASTM D4751)

• The ASTM method also called as the dry methodThe ASTM method, also called as the dry method uses glass beads of uniform size

• The test method involves in sieving uniform sized• The test method involves in sieving uniform sized glass beads through the geotextile

M i d i h i i l i l f• Main advantage is that it is relatively faster compared to other methods.


Procedure of AoS dry sieving test• Take 50 gm mass of smallest size glass beads (75) and sieve them for 10 minutes and determine the percentage retained on the geotextile. Repeat with next higher size g p gglass beads until the percentage of glass beads passing through is x% or less.

• A graph is drawn between glass bead size on X‐axis and g p gthe percent passing on Y‐axis

• If x% of a certain particle size is retained on a geotextile, the Ox of the geotextile is the size of the particle in mm x g p(usually 90% and 95% are used in the literature)

• ASTM designated AoS is O95 corresponding 5% particles passing through the geotextilep g g g



Equipments used for AoS test

15

10

fin

er

5perc

ent

0

10 10010 100

particle size (microns)

Typical data from dry sieve analysis on a woven geotextileTypical data from dry sieve analysis on a woven geotextileO90 = 150micronsO95 = 230 microns


Limitations & PrecautionsLimitations & Precautions

• Thick nonwoven geotextiles may entrap the glassThick nonwoven geotextiles may entrap the glass beads

• Yarns in some geotextiles may move during the• Yarns in some geotextiles may move during the test thus affecting the AoS value

Gl b d i l fl i d f i• Glass beads may simply float instead of going through the geotextile because of their low mass

• Electro‐static forces may develop thus affecting the results – anti‐static spray is used


Hydrodynamic Test Method for AoS

• Also called as wet sieving method.• Uniform size sand particles are used in the test. p

Geosynthetic with sand particles is repeatedly dipped in water and taken out. Percent of sand particles passing through the geotextile is determined after eachpassing through the geotextile is determined after each test.

• Procedure of test is similar to that using glass beads.g g• This procedure overcomes many of the limitations of

the dry sieve test• In some codes, well graded sand is washed down by

water and the soil particles collected below the geotextile are analysedgeotextile are analysed


No of cycles of immersion=100

R t 10/ i tRate=10/minute

quantity of sand=100 g

Hydrodynamic device used at IIT Madras for AoS test


y y

11/30Testing of Geosynthetics - 2

Filter design criteria

Fine soil particles should not be lost (piping limit)

f Pore opening size should be large enough for the water to flow through the geotextile freely (permeability limit)

Piping limit: O90 D85 of soil for granular soils

Permeability limit: O90 D15 of soil

d O 0 05and O90 0.05 mm


Cross-plane permeability test (ASTM D4491)

Ath

kiAkq nn

Constant head test 50 mm head difference

qkt

n between the upper and lower surfaces of geotextile

hAt

Kn = permeability (m/s)

g

Water allowed to flow through an opening of 25

di t n

h = head difference (m)

A = area of flow (m2)

mm diameter

Volume of flow (>1 litre) in a given time (>30 seconds)

= permittivity (s‐1)

t=thickness of geotextile

a given time ( 30 seconds) is measured

Temperature correction q=flow rate (m3/s)needs to be applied finally


Cross-plane permeability test device

geotextile sample

water column

geotextile samplemanometersto measurehead of waterb dabove and

belowgeotextile


Cross-plane Permeability Test device

Water outlet


Numerical Example

Data from a test on cross-plane permeability is given below. Estimate the permeability coefficient and the permittivity.

1200 ml of water collected in 180 seconds under 50 mm head of water Thickness of the geotextile is 0 65 mmhead of water. Thickness of the geotextile is 0.65 mm. Diameter of the opening in the permeability device is 25 mm.

Flow rate q = 1200/180 = 6.67 ml/s = 6.67*10-6 m3/sA = /4*(0.025)2 = 4.91*10-4m2

H = 50 mm = 0.05 mP bilit ffi i t k /iA 1 77*10 4 /Permeability coefficient kn = q/iA = 1.77*10-4 m/s Permittivity = kn/t = 0.27/s


Falling head permeability testFalling head permeability test

hakhh

tAa

tk

f

on10log3.2

• kn = permeability coefficient• t = thickness of the geotextile

f t l b t til• a = area of water column above geotextile• A = area of flow (25 mm diameter)• ho = initial height of water column = 80 mm• h = final height of water column = 20 mm• hf = final height of water column = 20 mm• t = time taken for the water head to fall from ho to hf


In plane permeability Tests (ASTM D4716)

• Test is performed at different gradients ofTest is performed at different gradients of 0.25, 0.5 and 1.0

• Normal pressure is applied on the sample p pp p

• Minimum size of sample is 300 mm ×300mm

• Geotextile should be sandwiched betweenGeotextile should be sandwiched between two thick rubber sheets to prevent any leakage


Schematic of in plane permeability device

Length = Lgeotextile sample

Length L

gradient of flow, i = water head/length


In plane permeability device


In plane permeability Tests (ASTM D4716)

iiA )(

Constant head test

Lhiqtk

twikiAkq

p

pp

/;

)(

iw

k p ;

q = rate of flow (m3/s)k = in plane permeability coefficient (m/s)kp = in plane permeability coefficient (m/s)i = gradient of flow = h/Lh = head difference in flow (m)L length of the sample (m)L = length of the sample (m)w = width of the sample (m)t = thickness of the sample (m) t i i it ( 2/ 3/ )


= transmissivity (m2/s or m3/s‐m)

Numerical example – in plane flowData from an in plane transmissivity flow test on a jute geotextile is given below. Calculate the transmissivity and in plane permeability coefficient.permeability coefficient.

One liter of water collected in 60 seconds. Thickness of the geotextile is 2 mm. Width and length of the sample are 300 mm. Head difference = 300 mm.i = 300/300 = 1i = 300/300 = 1q = 1/60 = 0.0167 l/s = 1.67*10‐5 m3/skp = q/i*w*t = 1.67*10‐5/(1*0.3*2/1000) = 0.027 m/sp q ( ) = kp*t = 0.027*2/1000 = 5.55*10‐5 m2/s


3.00E‐05

2 00E 05

2.50E‐05

3.00E 05

sec)

1.50E‐05

2.00E‐05

rat

e (m

3 /s

5.00E‐06

1.00E‐05

Flow

0.00E+00

0 2 4 6 8 10 12

Pressure (kPa)

Variation of in plane flow rate with normal pressure


Radial in plane flow apparatus

rrqtk )/ln( 12h

tk p

2


Gradient Ratio Test (ASTM D5101)

overflow

100 mm soil column

geotextile50mm25mm

MANOMETERSPERMEAMETER


Flow through a soil underlain by a geotextile filter layer is analysedCompatibility between the two is established

Gradient ratio test• Flow through a soil underlain by a geotextile filter layer is analysedfilter layer is analysed

• Compatibility between the two is established

Diff t h d f t d• Different heads of water are measured

50/)(25/)( 12

hhhhGR

lh3

50/)( 23 hh

• Mass of piped particles = mass/sample areasoil

geotextileh1

h2

h3• For good compatibility between the

geotextile and soil, steady state GR value should be less than 3.

50mm25mm25mm


2.5

NON‐WOVEN WOVEN

1.5

2

VALU

E

0.5

1

GR V

0

0 10 20 30 40 50 60 70 80

TIME(HR)

Gradient ratio tests on two different types of geotextiles and beach sandAfter long time, steady state of flow is established


After long time, steady state of flow is established

Long term flow testLong term flow test

• The gradient ratio apparatus can also be usedThe gradient ratio apparatus can also be used for determining the permeability coefficient over long term Flow rates can be determinedover long term. Flow rates can be determined after establishing steady conditions and permeability coefficient can be determinedpermeability coefficient can be determined.

• Interpretation of test results as in the tests in soil mechanics laboratorysoil mechanics laboratory



Schematic results from long term permeability tests

RecapRecap

• Determination of different hydraulic propertiesDetermination of different hydraulic properties of geotextiles– Opening Size– Opening Size

– Cross‐plane permeability

Inplane permeability– Inplane permeability

– Gradient Ratio

L T Fl– Long Term Flow


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Testing of Geosynthetics