geosynthetics engineering: in theory and practice · permeability test constant head test falling...

GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE

Prof. J. N. Mandal

Department of civil engineering, IIT Bombay, Powai , Mumbai 400076, India. Tel.022-25767328email: [email protected]

Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

Module - 3LECTURE- 13

Geosynthetic properties and test methods


RECAP of previous lecture…..

Pullout or Anchorage resistance

Tensile behavior of Geomembranes

Tear resistance of Geomembranes

Seam in shear and seam in peel test

Hydraulic properties (Continue…)

Porosity

AOS

POA Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

Permittivity or cross plane permeability (ASTM D4491 and ISO 11058):

Permittivity

Main function of geosynthetic is filtration when waterflows perpendicular to the geosynthetic


From Darcy’s equation:

So, Permittivity = gg

n

A.hq

tk

gg

ngn A.th.kA.i.kq

Ψ = Permittivity (sec-1)q = Flow rate (m3/sec), Kn = Hydraulic conductivity (Normal to geosynthetic) (m/s), Ag = Area of geosynthetic = L x W (m2), h = Head lost (m), and tg = Thickness of geosynthetic (m).

gg

n

A.hq

tk


At different hydraulic gradients, the flow rate (q) will bedifferent. The slope of the q/Ag vs. h curve at the origingives the permittivity.


Permeability test Constant head test Falling head test

Constant Head permeability test

Let, total stored water at time ‘∆ t’ = Q (m3),

Flow rate (q) can be determined as,q = Q/ ∆ t (m3/ sec)

Now, Darcy’s equation is used to determine the permittivity.


Falling head permittivity test


f

i10

g hhlog

t.Aa3.2

Ψ = permittivity (sec-1)a = Area of stand pipe (m2),Ag = Area of geosynthetics (m2)hi = Initial head at time t0,hf = Final head at time tf, andt = tf - to = Change in time (sec)

From falling head test the permittivity can be expressed as,


Transmissivity or in - plane permeability (ASTM D4716 and ISO 12958):

Major function of geosynthetic is drainage when water flows along the plane of geosynthetic under applied load.

The test is conducted under a constant head.Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

From Darcy’s equation, we can derive the expression fortransmissivity,

ixwqt.kg

gp )t.w.(i.kA.i.kq ggpgp

ixwqt.kg

gp Transmissivity (θ) =

= transmissivity of geosynthetic (m2/sec)q = flow rate (m3/sec), kp = hydraulic conductivity (in-plane of geosynthetic) (m/sec), i = hydraulic gradient = (h/Lg), h = head loss (m), Lg = length of geosynthetics (m), and wg = width of geosynthetics (m) tg = thickness of geosynthetic (m)


At different hydraulic gradients, the flow rate (q) will bedifferent. The slope of q/wg vs. i curve at the origin gives thepermittivity.

Transmissivity test Full length in-plane flow Radial in-plane flow


Full length in-plane flow


Example: Length of the sample (Lg) = 200 mm, width of thesample (wg) = 100 mm, thickness of the sample = 0.5 mm,flow rate (q) = 1 x 10-6 m3/sec, head loss = 10 cm.Determine transmissivity and in-plane coefficient ofpermeability of the geotextile.

gg

ggp

Lhxw

qixw

qt.k

sec/m10x2

10x20010x10x10x100

10x1 25

3

23

6

sec/m04.010x5.0

10x2t

k 3

5

gp

Solution:


Radial in-plane flow


)rt2(drdhkq gp

drdhr)2(tkq gp

dhtk2r

drq gp htk2)rrln(q gp

i

o

)rrln(

h2qtk

i

ogp

According to Darcy’s law, q = kp. i. Ag

= transmissivity of geosynthetic (m2/sec or m3/ sec-m)ro = outer radius of geosynthetic sample, and ri = inner radius of geosynthetic sample, Δh = the constant head


Transmissivity decreases under high normal pressure aswell as arrives at a constant value after approximately 250kPa normal pressure. Beyond this pressure, the yarnsbecome dense and too much tight to carry the water.

Transmissivity increases with the increase in the mass perunit area.

Transmissivity of jute geotextile specimens


Endurance properties


Abrasion test or Abrasion resistance (ASTM D4886 and ISO 13427)

Schematic of abrasion test The sample is placed on a rubber platform. It is rotated upto 1000 cycles under a fixed abrasion wheel to abrade thegeotextile.

Geotextile specimen isdisk-shaped.

Inner diameter = 60 mm

outer diameter = 90 mm


Two abraded geotextile specimens are cut and tensilestrength test is conducted. Take the average value.

Also determine the tensile strength of non-abradedgeotextile.

%100xgeotextile abraded-nonofstrengthTensile

geotextileabradedofstrengthTensileabrasionafterretainedStrength


Ultraviolet (sunlight) degradation (ASTM D4355, ASTM D5208, ASTM D5970)

Specimens are exposed to ultraviolet exposure in a xenon-arc device at 0, 150, 300 and 500 hr. It consists of 120 min cycles: light only (90 min) and then water spray and light (30 min).

At least five samples aretested for the UV test onboth machine and cross-machine directions.

Device for ultraviolet degradation

Geosynthetics should be kept at site below 32°C.


Firstly, tensile strength of the specimens without UVexposure is determined in both machine and cross-machinedirections.

After UV tests, cut strip or ravel strip tensile tests arecarried on the exposed specimens. It will show thedeterioration of the exposed samples.

For polypropylene and polyethylene geogrid minimum 70%strength should be retained after 500 hour (ASTM D4355).

For polyester geogrid minimum 50% strength should beretained after 500 hour (ASTM D 4355).


Gradient ratio (clogging) test (CW-02215 and ASTM D5101)

Gradient ratio tests are conducted on soils having permeabilitymore than about 10-5 m/s. It is suitable for sandy and silty soils(K ≤ 10-7 m/sec).

Photographic view of gradient ratio test Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

Flow

SOIL

Geotextile

1

3

2

4

5 6

P5P3P6 P4 P2P1

Z2

Z1

1 To 6 Pizometer NumberZ1 = 25 mmZ2 = 50 mmGradient Ratio =

h2 /z2

h1 /z1

h1 =(p3 +p4 )/ 2

h2 =(p5 +p6 )/ 2


Gradient ratio (GR) = (h1/z1)/ (h2/z2)

h1 = head change (mm) from the bottom of the geotextile to25 mm of soil above the geotextile,

z1 = geotextile thickness (mm) plus 25 mm of soil,

h2 = Head change (mm) from 25 mm soil above geotextile to50 mm soil above the previous 25 mm

z2 = 50 mm of soil.

The acceptable criterion for gradient ratio (GR): GR < 1 (Piping) GR > 1 (Clogging) GR > 3 (Severe clogging) GR = 1 (Stable)


Hydraulic conductivity ratio (HCR) (clogging) test on soil-geotextile system (ASTM D 5567)

For soils with permeability less than 10-5 m/s, hydraulicconductivity ratio tests are conducted.


HCR test is conducted in three stages: First stage is to saturate the sample. Second stage is to carry out primary consolidation of thesample Third stage is to initialize the flow through marine clay-geotextile system The test is terminated when hydraulic conductivity of thesystem stabilizes.

sgo

sg

kk

HCR

ksg = hydraulic conductivity of the soil-geotextile system at any time

ksgo= initial hydraulic conductivity measured atthe outset of the permeation phase


Test method and Procedure

The marine clay-geotextile filter system compatibility undereffective stress condition was carried out by conductingHydraulic Conductivity Ratio (HCR) tests as specified byASTM D5567.

The test method requires placing of the soil and geotextilein a flexible-wall permeameter and the desired effectivestress and hydraulic gradient are controlled in the system.

Size of soil sample: cylindrical remoulded marine claysample of 75 mm diameter and 50 mm height at watercontent of 60 %.


Schematic diagram of hydraulic conductivity ratio (HCR) test equipment during permeation test stage.


Test carried out in three stages:

1. Saturation of soil sample: Done by increasing thecell and back pressure gradually till the Skempton’s Bvalue of 0.98 was achieved at the cell pressure of 227kPa and back pressure of 220 kPa.

2. Primary consolidation of soil: Carried out at 50 kPaeffective stress. The cell pressure was maintained at250 kPa and back pressure at 200 kPa. It took about 5days for the completion of primary consolidation ofsoil.

3. Permeation of soil – geotextile filter system:Carried out at hydraulic gradient = 10 and soil effectivestress = 50 kPa till the flow was stabilized.



Hydraulic Conductivity Ratio (HCR) and pore volume are calculated from the test.

sgo

sg

kk

HCR

Where,

ksg = hydraulic conductivity of the soil- geotextile system atany time = (Q/A. i)

ksgo= initial hydraulic conductivity measured at the outset ofthe permeation phase of the test

Q = quantity of water flow for the given time interval, t

A = cross-section area of soil sample = 44.15 cm2

i = hydraulic gradient along the system = 10


p

qpq V

VV

Vq = cumulative volume of flow that has passed through the

sample at any given time

Vp = pore volume of soil sample = n V

n = porosity of soil sample at the end of consolidation stage

V = initial volume of soil sample = 221 cm3/day

Pore volume flow (Vpq):

7.1VV)e1(ee ooc

)e1(

enc

c

eo = initial void ratio of soil sample = 2.11

ec = void ratio at the end of consolidation stage

ΔV = soil volume change at the end of consolidation stage

= 28.5 cm3

V = initial volume of soil sample = 221 cm3/day

For Marine clay - woven jute filter system,

63.0)7.11(

7.1n

Therefore,


For Marine clay - woven jute filter system,ksgo = 3.01 m/sec

Vp = pore volume of soil sample

= n V = 0.63 x 221 = 139.23 ≈ 140 cm3/day

For Marine clay - polypropylene filter system,ksgo = 3.20 m /sec

Vp = 142 cm3/day

ksgo= initial hydraulic conductivity measured at the outsetof the permeation phase of the test


Marine clay - woven jute filter system Marine clay - polypropylene filter system

Time (days)

Ksg at any given time x10-9(m/s) HCR Vq

(cm3/day)Vpq

(cm3/day)Ksg at any given time x10-9(m/s) HCR Vq

(cm3/day)Vpq

(cm3/day)

1 3.01 1.00 140 1 3.20 1.00 142 12 2.88 0.96 151 1.08 3.15 0.98 154 1.083 2.62 0.87 161 1.15 2.88 0.90 165 1.164 2.62 0.87 171 1.22 2.62 0.82 175 1.235 2.36 0.79 180 1.29 2.36 0.74 184 1.306 2.10 0.70 188 1.34 2.10 0.66 192 1.357 1.83 0.70 195 1.39 1.83 0.57 199 1.408 1.83 0.61 202 1.44 1.57 0.49 205 1.449 1.57 0.61 208 1.49 1.31 0.41 210 1.48

10 1.31 0.52 213 1.52 1.05 0.33 214 1.5111 1.05 0.44 217 1.55 1.18 0.37 218.5 1.5412 1.05 0.35 221 1.58 1.21 0.38 223.1 1.5713 0.81 0.30 224.1 1.60 1.10 0.34 227.3 1.6014 0.79 0.28 227.1 1.62 1.02 0.29 231.2 1.6315 0.81 0.28 230.2 1.64 1.00 0.29 235 1.6516 0.80 0.27 233.3 1.67 1.05 0.28 239 1.6817 0.78 0.26 236.2 1.69 0.97 0.28 242.7 1.7118 0.79 0.26 239.2 1.71 0.94 0.28 246.3 1.7319 0.76 0.25 242.1 1.73 0.92 0.28 249.9 1.7620 0.81 0.27 245.2 1.75 0.92 0.28 253.5 1.7921 0.79 0.26 248.2 1.77 0.92 0.28 257.1 1.81

Table HCR test results.


Graph of hydraulic conductivity of marine clay-geotextile filter system versus time

-Both the systems reached stable flow condition .The hydraulic conductivity in marine clay-woven jute filter systemreached stable flow condition after 17 days of initialization of flowthrough the system whereas, Marine clay-polypropylene filtersystem reached stable flow condition after 13 days.


Graph of hydraulic conductivity of marine clay-geotextile filter system versus time


Hydraulic conductivity ratio against pore volume flow

The reduction of hydraulic conductivity ratio in marine clay-woven jute filter system was 0.25 and in marine clay–polypropylene filter system was 0.28.


flow

Test samples after the test (a) marine clay (b) woven jute geotextile and (c) environmental scanning electron

Microscope image of woven jute geotextile showing clay at the surface (Sophisticated analytical instrument facility

(SAIF), IIT, Bombay).


Conclusions:

The hydraulic conductivity in marine clay-woven jute filtersystem reached stable flow condition after 17 days ofinitialization of flow through the system whereas marineclay-polypropylene filter system, reached stable flowcondition after 13 days.

For the given soil and hydraulic condition, the hydraulicconductivity ratio in marine clay-woven jute filter systemreduced to 0.25 and in marine clay–polypropylene filtersystem by 0.28.


Marine clay-woven jute filter system has filtrationcompatibility similar to marine clay – polypropylene filtersystem for the given hydraulic and soil condition.

Visibly no significant loss of clay fraction was observedin both the systems.


Proper selection of jute geotextile filter plays significant role in making of natural PVDs.

Basic requirements of geotextile filter are

Ability to retain soil

Adequate permeability

Resistance to clogging


Please let us hear from you

Any question?


Prof. J. N. Mandal

Department of civil engineering, IIT Bombay, Powai , Mumbai 400076, India. Tel.022-25767328email: [email protected]


geosynthetics engineering: in theory and practice · permeability test constant head test falling...

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