geosynthetics engineering: in theory and practice
TRANSCRIPT
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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
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Module - 3LECTURE- 12
Geosynthetic properties and test methods
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
RECAP of previous lecture…..
Puncture resistance test
Penetration resistance test (drop test)/ tear resistance
Tensile behavior of geogrid
Geogrid rib tensile strength
Geogrid junction (node) strength
Junction strength of geocell
Tensile strength of gabions
Direct shear test on geosynthetic
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Pullout or anchorage resistance
It is very important to compute the pullout capacity ofreinforcement to ensure stability of any reinforcedstructure like reinforced soil retaining wall, reinforcedslopes etc.
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Only interface friction is associated with geotextile
Both interface friction and passive resistance areassociated with geogrid.
Pullout resistance or anchorage capacity is expressed as theratio of pullout force to the width of the sample (kN/m)
Two basic mechanisms are involved to mobilize or transferpullout resistance between soil and geosynthetic
1) Interface friction, and2) Passive resistance
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Pictorial view of pull-out test Schematic view
Interaction coefficient of geotextile (Ci)
Pr = F/W = 2. L. n. Ci. tan
tan)h(L2PC
q
ri
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Cellular reinforcement
Stress distribution in cellular reinforcement
FEM analysis of pull-out test on cellular reinforcement
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Ultimate pullout load was found increasing withincreasing height of the reinforcement up to 30 mm,
Further increase in height shows the decrease inultimate pullout resistance.
The optimization analysis shows that the spacing toheight ratio of 3.3 gives the maximum pulloutresistance for cellular reinforcements.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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P = 65kN/m; Le= 1m; = 30˚;q = 60kpa.
Solution:σn = γ x h + q = 20x0.3 + 60 = 66 kPa
P = 2 Ci Le σn tan
66 = 2xCix1x66xtan30˚
Ci = (66)/ (2x66x0587) = 0.849
Interaction coefficient = Ci = 0.849
Determine interaction coefficient. The following data is given.
Example:
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Tensile behavior of geomembrane
Dumbbell shaped test specimen
Smooth high density polyethylene (HDPE) and textured highdensity polyethylene (HDPE) geomembrane are used forconducting dumbbell shaped tests.
Test specimens are dyingcut from large sheets
ASTM D 638, D 882,D 6693 (Dumbbell shape)
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Tensile behavior of dumbbell shaped geomembraneProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Tensile behavior of wide width shaped Geomembrane issuitable in plain strain condition and much more designoriented compared to dumbbell shaped geomembrane
Specimen is 200 wide with 100 mm gauge length
Strain rate = 1 mm/ minute
Wide width geomembrane (ASTM D4885)
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Greater width of the specimen minimizes the contractionedge effect (necking) and provides closer results to actualmaterial behavior (ASTM D4885).
Tensile behavior of wide width shaped geomembrane (Smooth and textured HDPE)
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Tensile property
Dumbbell shape Narrow width (25 mm)
Wide width(200 mm)
ASTM D638 ASTM D882 ASTM D4885Smooth Textured Smooth Textured Smooth Textured
Strength at yield (kN/m)
30.3 27.7 28.0 27.54 26.0 24.0
Elongation at yield (%)
10.4 9.6 16.5 15.0 15.5 15. 0
Strength at break (kN/m)
28.19 29.5 - - - -
Elongation at break (%)
435 358 > 500 > 500 > 500 > 500
Tensile behavior of smooth and textured 1.5 mm thick HDPEgeomembrane
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Tear resistance of Geomembrane (ASTM D 1004, D2263, D5884, D751, D1424, D1938, and ISO 34)
Tearing resistance of geomembrane (a) schematic view and (b) pictorial view
The specimen has a 90degree angle.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Equipments for joining geomembrane
Geomembranes can be joined for seam in shear andseam in peel test.
Some typical seams of geomembrane
(After Giroud, 1994)
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Hydraulic properties
Porosity
Apparent opening size
Percent open area
Permittivity or cross plane permeability
Transmissivity or In- plane permeability
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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PorosityPorosity (n) = (Volume of void / Total volume) = Vv / V
Total volume (V) = Vs + Vv
Vs = volume of solid = ( m. A) /,m = mass per unit area (g/m2),A = Area (m2), = density (g/m3),Vv = volume of void,V = total volume = A. tgtg = thickness of geosynthetics.
VV1
VVV
VVn ssv
gg t.m1
t.A
A.m
1n
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Apparent Opening Size (A.O.S.) or Equivalent Opening Size (E.O.S) [ASTM D4751]
Apparent opening size can be measured in four ways:1. By sieving glass beads2. By image analyzers (Gours et al. 1982), and 3. By mercury intrusion (Holtz, 1988)4. By bubble point method (Bhatia et al., 1996)
Pictorial view of the glass beads of different sizes Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Determination of apparent opening size by dry glass sieving method
The size of the beads which passes by less than or equal to 5 % is represented as Apparent opening size (A.O.S.) or O95 expressed in millimeters.
The O95 value is specifically used for design of any hydraulic structure.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Apparent opening size of different geotextile filters
Apparent opening size of geotextile decreases withincrease in the weight of geotextile.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Percent open area (POA)Percent open area can be defined as the ratio of total openarea or total voids area of the geotextile to the total area ofgeotextile. It is expressed in percentage (%).
geotextileofareaTotalgeotextileofopeningstheofareaTotalPOA
The open area is measured by passing a light through thegeotextile to a poster sized cardboard which is in the form ofa graph sheet. From the graph sheet, number of squares canbe counted. Otherwise, the voids can be mapped by aplanimeter.
Total area is measured by same magnification.Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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As the filaments of non woven geotextiles are closelytightened and very random, light cannot pass through itproperly and as a consequence, the light passing method isnot suitable for it.
The percent open area (POA) for monofilament and slitfilm wovens should be greater than or equal to fourpercentage.
POA is applicable only for monofilament woven geotextile.
Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay
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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