USE OF GEOGRIDS IN
FLEXIBLE PAVEMENT
GUIDED BY,
PRESENTED BY,
Prof. K.A.MOHANDAS
CHINNU MOL.M
ROLL NO 24
S8CA
INTRODUCTION
•
Difficulty in the development and maintenance of pavement with limited
financial resources
•
Unavailability of high quality materials
•
Geosynthetics- commercial construction aid
Separation
Reinforcement
Filtration
Drainage
Containment
•
Geogrid gained increasing acceptance in road construction
GEOGRIDS





Made from polymers
Openings between adjacent longitudinal and
transverse ribs called apertures
Formed by regular network of integrally
connected elements with apertures > ¼”
Longitudinal and transverse ribs meet at junctions
(nodes)
Both rib strength and junction strength are
important
TYPES
WOVEN
GEOGRIDS
GEOGRID
COMPOSITES
EXTRUDED
GEOGRIDS
WELDED
GEOGRIDS
UNIAXIAL
PRE-TENSIONED IN
ONE DIRECTION
EXTRUDED
GEOGRIDS
BIAXIAL
PRE-TENSIONED IN
TWO DIRECTIONS
FUNCTIONS

Separation


Secondary function
Reinforcement


Primary function
Improves engineering properties of pavement
system
APPLICATIONS

Mechanical subgrade stabilization

Aggregate base reinforcement

Asphalt Concrete (AC) overlay reinforcement
USES

Construction aid over soft subgrades

Improve service life

Reduce structural cross-section for given service life
REINFORCEMENT MECHANISMS

LATERAL RESTRAINT

IMPROVED BEARING CAPACITY

TENSIONED MEMBRANE EFFECT
LATERAL RESTRAINT
IMPROVED BEARING CAPACITY
TENSIONED MEMBRANE EFFECT
MATERIAL PROPERTIES
Commonly Reported Engineering Properties of Geogrids
Engineering Property
Test Method
Units
2% or 5% Secant Moduli
ASTM D 6637
kN/m
Coefficient of Pullout Interaction
GRI GG5
-
Coefficient of Direct Shear
ASTM D 5321
Degrees
Aperture Size
Direct Measure
Mm
Percent Open Area
COE CW-02215
%
Ultimate Tensile Strength
ASTM D 6637
kN/m
Junction Strength
GRI GG2
%
Ultraviolet Stability
ASTM D 4355
%
Minimum Geotextile Specification Requirements
Geotextile Property
ASTM Test Method
Min. Requirement
Grab Strength (lb)
D 4632
200
Puncture Strength (lb)
D 4833
80
Burst Strength (psi)
D 3786
250
Trapezoid Tear (lb)
D 4533
80
Apparent Opening Size (mm)
D 4751
< 0.43
Permittivity (secˉ¹)
D 4491
0.05
Ultraviolet Degradation (% Retained
Strength @ 500 hr)
D 4355
50
Polymer Type
-
PET or PP
AGGREGATE-SURFACED REINFORCED
PAVEMENT DESIGN
•
First step is to determine the properties of subgrade
o
Grain-size distribution
o
Atterberg limits
o
In-situ shear strength
Vane shear test
CBR test
DCP test
GEOSYNTHETIC APPLICABILITY FOR
SUBGRADES OF DIFFERENT CBR RATIO
CBR ≤ 0.5
Nonwoven Geotextile
Biaxial Geogrid
0.5 < CBR ≤ 2.0
Reduction in aggregate thickness
2.0 < CBR ≤ 4.0
Geotextile is required for finegrained subgrades
CBR > 4.0
Geogrid reinforcement generally
considered cost-prohibitive
RELATIONSHIP BETWEEN CONE INDEX,
CBR AND SHEAR STRENGTH (C)
Design Procedure
1.
Determination of the Subgrade Shear Strength (C)
Directly measured using vane shear devices
Converting from CBR to Shear Strength
1.
Determination of Design Traffic
Based upon the gear configuration of heaviest
vehicle expected in the traffic mix
Single-wheel Load
Dual-wheel Load
Tandem-wheel Load
The combined weight on the selected gear is used
as the design vehicle weight
3.
Determination of the Reinforced Bearing Capacity Factor (Nc)
The Unreinforced Bearing Capacity Factor = 2.8
The Reinforced Bearing Capacity Factor Recommendations:-
GEOTEXTILE
GEOGRID
BOTH
0.5 < CBR ≤ 2.0
0.5
6.7
6.7
2.0 < CBR ≤ 4.0
0.5
6.7
6.7
CBR VALUE
≤ 0.5
>4.0
4 . Determination of the Required Aggregate Thickness
The minimum aggregate thickness is 6 inches
Thickness is obtained from Design Curve
Subgrade Bearing Capacity (CNc) on X-axis
Subgrade Bearing Capacity = Shear Strength x Bearing Capacity Factor
Required aggregate thickness on Y-axis
CONSTRUCTION OF GEOSYNTHETICREINFORCED PAVEMENTS
RECOMMENDED PROCEDURE:-
1.
Geotextile Installation
1.
Geogrid Installation
1.
Aggregate Placement
GEOTEXTILE INSTALLATION
If CBR < 2.0 vegetation and surface mats should not be removed
If CBR ≥ 2.0
subgrade should be compacted
stumps, roots, etc. should be removed
If CBR > 0.5 geotextile is laid in the direction in which the aggregate will be laid
If CBR ≤ 5 geotextile is laid transverse to the direction of the traffic lane
Geosynthetic Overlap Requirements For Use Pavements
GEOGRID INSTALLATION
Site should be cleaned
Geogrid should be rolled out by hand directly on subgrade/geotextile
for design aggregate thickness < 14 in.
For thickness > 14 in. it should be placed in the middle of aggregate
layer
It can be held in places using staples, pins or sand bags for windy
conditions
CONCLUSION
•
The positive effects of geogrid reinforced base courses can
economically and ecologically be utilized to reduce reinforced
aggregate thickness
•
The design engineer should be well aware of possible problems and
should use this relative new tool for solving them
•
For this he should understand properties and capabilities of the geogrid
materials at hand
REFERENCE
1.Christopher, B.R. And Perkins, S.W., 2008. “Full Scale Testing of Geogrids to Evaluate
Junction Strength Requirements for Reinforced Roadway Base Design,” Proceedings of
the Fourth European Geosynthetics Conference, Edinburgh, United Kingdom,
International Geosynthetics Society.
2.Cuelho, E.G. and Perkins, S.W., 2009. Field Investigation of Geosynthetics used for subgrade
Stabilization, Summary Report 8193, Montana Department of Transportation, 4 p.
(http://www.mdt.mt.gov/research/projects/geotech/subgrade.shtml).
3.Holtz, R.D., Christopher, B.R., and Berg, R.R., 2008. Geosynthetic Design and
Construction Guidelines, Participant Notebook, FHWA Publication No. FHWA HI -07092, Federal Highway Administration, Washington, D.C., 592 p.
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