1. USE OF GEOGRIDS IN FLEXIBLE PAVEMENT
GUIDED BY, PRESENTED BY,
Prof. K.A.MOHANDAS CHINNU MOL.M
ROLL NO 24
S8CA

2. 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

3. 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

4. TYPES
EXTRUDED
GEOGRIDS
WOVEN
WELDED
GEOGRID
COMPOSITES

5. EXTRUDED GEOGRIDS UNIAXIAL BIAXIAL PRE-TENSIONED IN ONE DIRECTION
PRE-TENSIONED IN TWO DIRECTIONS

6. FUNCTIONS Reinforcement Improves engineering properties of pavement
Separation
Reinforcement
Secondary function
Primary function
Improves engineering properties of pavement
system

7. USES Improve service life
Construction aid over soft subgrades
Improve service life
Reduce structural cross-section for given service life

8. APPLICATIONS Mechanical subgrade stabilization
Aggregate base reinforcement
Asphalt Concrete (AC) overlay reinforcement

9. REINFORCEMENT MECHANISMS
LATERAL RESTRAINT
IMPROVED BEARING CAPACITY
TENSIONED MEMBRANE EFFECT

10. LATERAL RESTRAINT

11. IMPROVED BEARING CAPACITY

12. TENSIONED MEMBRANE EFFECT

13. 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
Junction Strength
GRI GG2
Ultraviolet Stability
ASTM D 4355

14. 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
Apparent Opening Size (mm)
D 4751
< 0.43
Permittivity (secˉ¹)
D 4491
0.05
Ultraviolet Degradation (% Retained 500 hr)
D 4355 50
Polymer Type -
PET or PP

15. Minimum Biaxial Geogrid Specification Requirements
Geogrid Property
ASTM Test Method
Min. Requirement
Mass per Unit Area (oz/yd²)
D 5261
9.0
Aperture size-MD (in.)
Direct Measure
1.0
Aperture Size-CMD (in.)
1.3
Wide Width Strip Tensile Strength (lb/ft)
5% Strain-MD
5% Strain-CMD
Ultimate Strength-MD
Ultimate Strength-CMD
D 6637
700
1200
2096
Manufacturing Process _
Punched $ Drawn

16. AGGREGATE-SURFACED REINFORCED PAVEMENT DESIGN
First step is to determine the properties of subgrade
Grain-size distribution
Atterberg limits
In-situ shear strength
Vane shear test
CBR test
DCP test

17. GEOSYNTHETIC APPLICABILITY FOR SUBGRADES OF DIFFERENT CBR RATIO
Nonwoven Geotextile
Biaxial Geogrid
Reduction in aggregate thickness
Geotextile is required for fine-
grained subgrades
Geogrid reinforcement generally
considered cost-prohibitive
RELATIONSHIP BETWEEN CONE INDEX, CBR AND SHEAR STRENGTH (C)

18. Design Procedure Determination of the Subgrade Shear Strength (C)
Determination of Design Traffic
Directly measured using vane shear devices
Converting from CBR to Shear Strength
Based upon the gear configuration of heaviest
vehicle expected in the traffic mix
The combined weight on the selected gear is used
as the design vehicle weight
Single-wheel Load
Dual-wheel Load
Tandem-wheel Load

19. Determination of the Reinforced Bearing Capacity Factor (Nc) CBR VALUE
The Unreinforced Bearing Capacity Factor = 2.8
The Reinforced Bearing Capacity Factor Recommendations:-
CBR VALUE
GEOTEXTILE
GEOGRID
BOTH
≤ 0.5
0.5 < CBR ≤ 2.0
0.5
6.7
2.0 < CBR ≤ 4.0
>4.0

20. 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
Required aggregate thickness on Y-axis
Subgrade Bearing Capacity = Shear Strength x Bearing Capacity Factor

24. REINFORCED FLEXIBLE PAVEMENT DESIGN
DESIGN PROCEDURE:-
1. Determination of the Pavement Layer Properties
CBR ≤ 0.5
0.5 < CBR ≤ 4.0
4.0 < CBR ≤ 8.0
CBR > 8.0
No aggregate
thickness
reduction is
recommended
Geotextile is
recommended for
fine-grained
subgrades
generally not
The design
subgrade strength
exceeds the
existing database
Consider a base
course reduction
factor

25. 2. Determine Design Traffic
The Design Index (DI) combines the effect of average vehicle axle
loadings and expected traffic volume

26. 3. Determination of Required Layer Thickness

27. MINIMUM THICKNESS FOR SURFACE AC AND BASE COURSE
Design Aggregate Thickness = Total Required Pavement Thickness –
The Minimum AC Thickness

28. CONSTRUCTION OF GEOSYNTHETIC-REINFORCED PAVEMENTS
RECOMMENDED PROCEDURE:-
Geotextile Installation
Geogrid Installation
Aggregate Placement

29. GEOTEXTILE INSTALLATION
If CBR < 2.0 vegetation and surface mats should not be removed
If CBR ≥ 2.0
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
subgrade should be compacted
stumps, roots, etc. should be removed
Geosynthetic Overlap Requirements For Use Pavements

30. 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

31. AGGREGATE PLACEMENT CBR < 1.0
Aggregate is placed in the centre at a depth greater than the final
design grade
Spread excess aggregate laterally to the shoulders of the roadway
It is compacted to the design thickness
Full design aggregate thickness is placed in one lift
CBR between 1.0 and 3.0

32. 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

33. THANK YOU