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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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
At different hydraulic gradients, the flow rate (q) will bedifferent. The slope of the q/Ag vs. h curve at the origingives the permittivity.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Falling head permittivity test
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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,
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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)
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Full length in-plane flow
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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:
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Radial in-plane flow
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
)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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Endurance properties
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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).
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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)
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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 %.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Schematic diagram of hydraulic conductivity ratio (HCR) test equipment during permeation test stage.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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,
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
Graph of hydraulic conductivity of marine clay-geotextile filter system versus time
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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).
Prof. J. N. Mandal, Department of Civil Engineering, 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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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