GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE Prof. J. N. Mandal Department of civil enineerin, IIT Bombay, Powai, Mumbai 400076, India. Tel.022-25767328 email: cejnm@civil.iitb.ac.in
Module - 3 LECTURE- 13 Geosynthetic properties and test methods
RECAP of previous lecture.. Pullout or Anchorae resistance Tensile behavior of Geomembranes Tear resistance of Geomembranes Seam in shear and seam in peel test Hydraulic properties (Continue ) Porosity AOS POA
Permittivity or cross plane permeability (ASTM D4491 and ISO 11058): Permittivity Main function of eosynthetic is filtration when water flows perpendicular to the eosynthetic
From Darcy s equation: q k n.i.a k n. h t. A k t n q h.a So, Permittivity = k t n q h.a Ψ = Permittivity (sec -1 ) q = Flow rate (m 3 /sec), K n = Hydraulic conductivity (Normal to eosynthetic) (m/s), A = Area of eosynthetic = L x W (m 2 ), h = Head lost (m), and t = Thickness of eosynthetic (m).
At different hydraulic radients, the flow rate (q) will be different. The slope of the q/a vs. h curve at the oriin ives the permittivity.
Permeability test Constant head test Fallin head test Constant Head permeability test Let, total stored water at time t = Q (m 3 ), Flow rate (q) can be determined as, q = Q/ t (m 3 / sec) Now, Darcy s equation is used to determine the permittivity.
Fallin head permittivity test
From fallin head test the permittivity can be expressed as, a 2.3 A. t lo 10 h h i f Ψ = permittivity (sec -1 ) a = Area of stand pipe (m 2 ), A = Area of eosynthetics (m 2 ) h i = Initial head at time t 0, h f = Final head at time t f, and t = t f - t o = Chane in time (sec)
Transmissivity or in - plane permeability (ASTM D4716 and ISO 12958): Major function of eosynthetic is drainae when water flows alon the plane of eosynthetic under applied load. The test is conducted under a constant head.
From Darcy s equation, we can derive the expression for transmissivity, q k p.i.a k p.i.( w. t ) k p.t w q x i Transmissivity (θ) = k p.t q w x i = transmissivity of eosynthetic (m 2 /sec) q = flow rate (m 3 /sec), k p = hydraulic conductivity (in-plane of eosynthetic) (m/sec), i = hydraulic radient = (h/l ), h = head loss (m), L = lenth of eosynthetics (m), and w = width of eosynthetics (m) t = thickness of eosynthetic (m)
At different hydraulic radients, the flow rate (q) will be different. The slope of q/w vs. i curve at the oriin ives the permittivity. Transmissivity test Full lenth in-plane flow Radial in-plane flow
Full lenth in-plane flow
Example: Lenth of the sample (L ) = 200 mm, width of the sample (w ) = 100 mm, thickness of the sample = 0.5 mm, flow rate (q) = 1 x 10-6 m 3 /sec, head loss = 10 cm. Determine transmissivity and in-plane coefficient of permeability of the eotextile. Solution: k p.t q w x i w q x h L 100 x10 1 5 2x10 2 2 m 3 3 6 x10 10 x10 x 200 x10 / sec t 2x10 0.5x10 5 k p 3 0.04 m / sec
Radial in-plane flow
Accordin to Darcy s law, q = k p. i. A q k p dh dr (2rt ) q k p t (2)r dh dr q dr r 2k p t dh q ln( r r o i ) 2 k p t h k p t q 2h ln( r r o i ) = transmissivity of eosynthetic (m 2 /sec or m 3 / sec-m) r o = outer radius of eosynthetic sample, and r i = inner radius of eosynthetic sample, Δh = the constant head
Transmissivity of jute eotextile specimens Transmissivity increases with the increase in the mass per unit area. Transmissivity decreases under hih normal pressure as well as arrives at a constant value after approximately 250 kpa normal pressure. Beyond this pressure, the yarns become dense and too much tiht to carry the water.
Endurance properties
Abrasion test or Abrasion resistance (ASTM D4886 and ISO 13427) Schematic of abrasion test Geotextile specimen is disk-shaped. Inner diameter = 60 mm outer diameter = 90 mm The sample is placed on a rubber platform. It is rotated up to 1000 cycles under a fixed abrasion wheel to abrade the eotextile.
Two abraded eotextile specimens are cut and tensile strenth test is conducted. Take the averae value. Also determine the tensile strenth of non-abraded eotextile. Strenth retained after abrasion Tensile strenth Tensile strenth of of abraded eotextile non - abraded eotextile x 100 %
Ultraviolet (sunliht) deradation (ASTM D4355, ASTM D5208, ASTM D5970) Device for ultraviolet deradation At least five samples are tested for the UV test on both machine and crossmachine directions. Geosynthetics should be kept at site below 32 C. Specimens are exposed to ultraviolet exposure in a xenonarc device at 0, 150, 300 and 500 hr. It consists of 120 min cycles: liht only (90 min) and then water spray and liht (30 min).
Firstly, tensile strenth of the specimens without UV exposure is determined in both machine and cross-machine directions. After UV tests, cut strip or ravel strip tensile tests are carried on the exposed specimens. It will show the deterioration of the exposed samples. For polypropylene and polyethylene eorid minimum 70% strenth should be retained after 500 hour (ASTM D4355). For polyester eorid minimum 50% strenth should be retained after 500 hour (ASTM D 4355).
Gradient ratio (cloin) test (CW-02215 and ASTM D5101) Gradient ratio tests are conducted on soils havin permeability more than about 10-5 m/s. It is suitable for sandy and silty soils (K 10-7 m/sec). Photoraphic view of radient ratio test
P 1 Flow P 3 P 5 P 6 P 4 P 2 5 6 h 1 =(p 3 +p 4 )/ 2 h 2 =(p 5 +p 6 )/ 2 Z 2 3 SOIL 4 Z 1 1 Geotextile 2 1 To 6 Pizometer Number Z 1 = 25 mm Z 2 = 50 mm h 1 /z 1 Gradient Ratio = h2 /z 2
Gradient ratio (GR) = (h 1 /z 1 )/ (h 2 /z 2 ) h 1 = head chane (mm) from the bottom of the eotextile to 25 mm of soil above the eotextile, z 1 = eotextile thickness (mm) plus 25 mm of soil, h 2 = Head chane (mm) from 25 mm soil above eotextile to 50 mm soil above the previous 25 mm z 2 = 50 mm of soil. The acceptable criterion for radient ratio (GR): GR < 1 (Pipin) GR > 1 (Cloin) GR > 3 (Severe cloin) GR = 1 (Stable)
Hydraulic conductivity ratio (HCR) (cloin) test on soil-eotextile system (ASTM D 5567) For soils with permeability less than 10-5 conductivity ratio tests are conducted. m/s, hydraulic
HCR test is conducted in three staes: First stae is to saturate the sample. Second stae is to carry out primary consolidation of the sample Third stae is to initialize the flow throuh marine clayeotextile system The test is terminated when hydraulic conductivity of the system stabilizes. HCR k k s so k s = hydraulic conductivity of the soileotextile system at any time k so = initial hydraulic conductivity measured at the outset of the permeation phase
Test method and Procedure The marine clay-eotextile filter system compatibility under effective stress condition was carried out by conductin Hydraulic Conductivity Ratio (HCR) tests as specified by ASTM D5567. The test method requires placin of the soil and eotextile in a flexible-wall permeameter and the desired effective stress and hydraulic radient are controlled in the system. Size of soil sample: cylindrical remoulded marine clay sample of 75 mm diameter and 50 mm heiht at water content of 60 %.
Schematic diaram of hydraulic conductivity ratio (HCR) test equipment durin permeation test stae.
Test carried out in three staes: 1. Saturation of soil sample: Done by increasin the cell and back pressure radually till the Skempton s B value of 0.98 was achieved at the cell pressure of 227 kpa and back pressure of 220 kpa. 2. Primary consolidation of soil: Carried out at 50 kpa effective stress. The cell pressure was maintained at 250 kpa and back pressure at 200 kpa. It took about 5 days for the completion of primary consolidation of soil. 3. Permeation of soil eotextile filter system: Carried out at hydraulic radient = 10 and soil effective stress = 50 kpa till the flow was stabilized.
Hydraulic Conductivity Ratio (HCR) and pore volume are calculated from the test. Where, HCR k k s so k s = hydraulic conductivity of the soil- eotextile system at any time = (Q/A. i) k so = initial hydraulic conductivity measured at the outset of the permeation phase of the test Q = quantity of water flow for the iven time interval, t A = cross-section area of soil sample = 44.15 cm 2 i = hydraulic radient alon the system = 10
Pore volume flow (V pq ): V pq V V q p V q = cumulative volume of flow that has passed throuh the sample at any iven time V p = pore volume of soil sample = n V n = porosity of soil sample at the end of consolidation stae V = initial volume of soil sample = 221 cm 3 /day
For Marine clay - woven jute filter system, n e (1 c e c ) e c e o (1 e o V ) V 1.7 Therefore, n 1.7 (1 1.7) 0.63 e o = initial void ratio of soil sample = 2.11 e c = void ratio at the end of consolidation stae ΔV = soil volume chane at the end of consolidation stae = 28.5 cm 3 V = initial volume of soil sample = 221 cm 3 /day
For Marine clay - woven jute filter system, k so = 3.01 m/sec V p = pore volume of soil sample = n V = 0.63 x 221 = 139.23 140 cm 3 /day For Marine clay - polypropylene filter system, k so = 3.20 m /sec V p = 142 cm 3 /day k so = initial hydraulic conductivity measured at the outset of the permeation phase of the test
Table HCR test results. Marine clay - woven jute filter system Marine clay - polypropylene filter system Time (days) Ks at any iven time x10-9 (m/s) HCR Vq (cm 3 /day) Vpq (cm 3 /day) Ks at any iven time x10-9 (m/s) HCR Vq (cm 3 /day) Vpq (cm 3 /day) 1 3.01 1.00 140 1 3.20 1.00 142 1 2 2.88 0.96 151 1.08 3.15 0.98 154 1.08 3 2.62 0.87 161 1.15 2.88 0.90 165 1.16 4 2.62 0.87 171 1.22 2.62 0.82 175 1.23 5 2.36 0.79 180 1.29 2.36 0.74 184 1.30 6 2.10 0.70 188 1.34 2.10 0.66 192 1.35 7 1.83 0.70 195 1.39 1.83 0.57 199 1.40 8 1.83 0.61 202 1.44 1.57 0.49 205 1.44 9 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 1.51 11 1.05 0.44 217 1.55 1.18 0.37 218.5 1.54 12 1.05 0.35 221 1.58 1.21 0.38 223.1 1.57 13 0.81 0.30 224.1 1.60 1.10 0.34 227.3 1.60 14 0.79 0.28 227.1 1.62 1.02 0.29 231.2 1.63 15 0.81 0.28 230.2 1.64 1.00 0.29 235 1.65 16 0.80 0.27 233.3 1.67 1.05 0.28 239 1.68 17 0.78 0.26 236.2 1.69 0.97 0.28 242.7 1.71 18 0.79 0.26 239.2 1.71 0.94 0.28 246.3 1.73 19 0.76 0.25 242.1 1.73 0.92 0.28 249.9 1.76 20 0.81 0.27 245.2 1.75 0.92 0.28 253.5 1.79 21 0.79 0.26 248.2 1.77 0.92 0.28 257.1 1.81
Graph of hydraulic conductivity of marine clay-eotextile filter system versus time -Both the systems reached stable flow condition. The hydraulic conductivity in marine clay-woven jute filter system reached stable flow condition after 17 days of initialization of flow throuh the system whereas, Marine clay-polypropylene filter system reached stable flow condition after 13 days.
Graph of hydraulic conductivity of marine clay-eotextile filter system versus time
Hydraulic conductivity ratio aainst pore volume flow The reduction of hydraulic conductivity ratio in marine claywoven 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 eotextile and (c) environmental scannin electron Microscope imae of woven jute eotextile showin clay at the surface (Sophisticated analytical instrument facility (SAIF), IIT, Bombay).
Conclusions: The hydraulic conductivity in marine clay-woven jute filter system reached stable flow condition after 17 days of initialization of flow throuh the system whereas marine clay-polypropylene filter system, reached stable flow condition after 13 days. For the iven soil and hydraulic condition, the hydraulic conductivity ratio in marine clay-woven jute filter system reduced to 0.25 and in marine clay polypropylene filter system by 0.28.
Marine clay-woven jute filter system has filtration compatibility similar to marine clay polypropylene filter system for the iven hydraulic and soil condition. Visibly no sinificant loss of clay fraction was observed in both the systems.
Proper selection of jute eotextile filter plays sinificant role in makin of natural PVDs. Basic requirements of eotextile filter are Ability to retain soil Adequate permeability Resistance to cloin
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Prof. J. N. Mandal Department of civil enineerin, IIT Bombay, Powai, Mumbai 400076, India. Tel.022-25767328 email: cejnm@civil.iitb.ac.in