GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE 12.pdf · planimeter. Total area is measured by same magnification. Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay

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- 12

Geosynthetic properties and test methods



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

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.

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


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


Cellular reinforcement

Stress distribution in cellular reinforcement

FEM analysis of pull-out test on cellular reinforcement


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.


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:


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)


Tensile behavior of dumbbell shaped geomembraneProf. J. N. Mandal, Department of Civil Engineering, IIT Bombay

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)


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)


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


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.


Equipments for joining geomembrane

Geomembranes can be joined for seam in shear andseam in peel test.

Some typical seams of geomembrane

(After Giroud, 1994)


Hydraulic properties

Porosity

Apparent opening size

Percent open area

Permittivity or cross plane permeability

Transmissivity or In- plane permeability


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


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

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.


Apparent opening size of different geotextile filters

Apparent opening size of geotextile decreases withincrease in the weight of geotextile.


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

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.


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]


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GEOSYNTHETICS ENGINEERING: IN THEORY AND PRACTICE 12.pdf · planimeter. Total area is measured by same magnification. Prof. J. N. Mandal, Department of Civil Engineering, IIT Bombay