1. Geosynthetic in Road Pavement and associated Works

2. Typical Problem of Low Bearing Capacity

3. FAILURE CRITERIA FUNCTIONAL STRUCTURAL SERVICEABILITY RUTTING FATIGUE
DRAINAGE/ MOISTURE
RUTTING
FATIGUE
REFLECTIVE AND LONGITUDINAL CRACKING
CONTAMINATION
SERVICEABILITY
LOW TEMPERATURE CRACKING

4. Increase in traffic volume Contamination of road material
WHAT CAUSES ROAD PAVEMENTS TO FAIL?
Poor drainage
Increase in traffic volume
Contamination of road material
Short term design
Increase in traffic loads
Insufficient strength of road material
Poor existing soil properties
Defects in construction method and quality control

5. Pavement – Typical components
Typical Asphalt Pavements
WEARING COURSE
BINDER
BASE
FOUNDATION
SUBGRADE
Main structural element (durable)
BOUND MATERIAL
Pavement foundation
GRANULAR MATERIAL OVER SOIL
Existing soil
BOUND MATERIAL: high stiffness, crack and deformation resistant
GRANULAR MATERIAL OVER SOIL: adequate platform to place layer above 2

6. Geosynthetics in Pavements - Today
More common and well known, well established solution
Used as an alternative to conventional system
Considered as cost-effective solution
Basic Application includes:
1. Subgrade Separation and Stabilization
2. Base reinforcement
3. Overlay stress absorption and reinforcement
4. Drainage arrangement

7. 1. Subgrade Separation and Stabilization

8. Subgrade Separation
The placements of a flexible porous textile between dissimilar materials so that the integrity and functioning of both materials can be remain intact or are improved.
Nonwoven Geotextile is used between subgrade and base course to prevent the intermixing of subgrade and base course aggregate
Adopted when subgrade is strong enough (CBR > 3.0)
If CBR is weak then subgrade stabilization is also required by providing high strength geotextile or geogrid

9. Concept of geotextile separation in roadways (after Rankilor, 1981)
Subgrade Separation
Concept of geotextile separation in roadways (after Rankilor, 1981)

10. Without Separation – Base Stone Fouling Occurs
Fouling of the base aggregate gradually reduces the quality and strength of the base aggregate.
Rigid Pavement
Flexible Pavement

11. Intermixing problem of aggregate and subsoil
“If you combine 10 kg of stone and 10 kg of mud, you have 20 kg of mud” and the associated loss of support!

12. SUBGRADE STABILIZATION
For larger rut depths, more strain is induced in the geosynthetic. In this case, considerable reduction in aggregate thickness is possible by the use of a stronger geosynthetic.
If subgrade CBR is very weak (CBR<1.5) proper stabilization is required by providing high strength geotextile or geogrid.
It provides lateral restraint to the subgrade which increases the allowable bearing capacity of the subgrade

13. SUBGRADE STABILIZATION
A stabilization geotextile/geogrid facilitates ease of construction over weak subgrade
A geogrid is effective in reducing the required fill over a weak subgrade

14. Summary for Separation and Stabilization
The following general conclusions can be drawn relating to a typical
road base:
A geosynthetic that functions primarily as a separator (typically when the subgrade CBR  3) will increase the allowable bearing capacity of the subgrade by 40-50% (separation geotextiles)
A geosynthetic that functions primarily to provide confinement of the aggregate and lateral restraint to the subgrade (typically when the subgrade CBR < 3) will both increase the allowable bearing capacity of the subgrade and provide an improved load distribution ratio in the aggregate. The combined benefits can enhance load carrying capacity of the road by well over 50% (stabilization geogrids or geotextiles)
With very weak subgrade (CBR<1.5), it is often beneficial to combine the benefits of both separation and stabilization

15. 2. Base reinforcement

16. BASE REINFORCEMENT
Permanent roads carry larger traffic volumes and typically have asphalt or portland cement concrete surfacing over a base layer of aggregate.
With the addition of an appropriate geosynthetic, the Soil-Geosynthetic-Aggregate (SGA)
system gains stiffness via
“confinement” of the
aggregate.

17. Geogrid base reinforcement, confines and stiffens the aggregate base layer providing long-term support for the paved surface by: A. Preventing lateral spreading of the base B. Increasing confinement and thus stiffness of the base C. Improving vertical stress distribution on the subgrade

18. The unique structure allows the grid to get a good “grip” on the aggregate particles and results in effective mechanical interlock.
The unique shape of the geogrid ribs confines aggregate particles due to its high stiffness and the strength at the corners (junctions), just like a rack confines billiard balls.

19. 3. Overlay stress absorption and reinforcement

20. Reflective Cracking in Pavements
Many pavements, which are considered to be structurally sound after the construction of an overlay, prematurely exhibit a cracking pattern similar to that which existed in the underlying pavement – Reflection Cracking
Reflective cracks
A. destroy surface continuity
B. decrease structural strength
C. allow water to enter sub-layers.
Thus, the problems that weakened
the old pavement are extended up
into the new overlay.

21. Solution for Reflecting Cracking
Overlay reinforcement by:
Glass Grid
Geogrid made of glass fibers

22. Crack Reflection Solutions
APPLICATIONS
Geogrids
Crack Reflection Solutions

23. Surface Rutting Solution
APPLICATIONS
Geogrids
Surface Rutting Solution

24. Fatigue Cracking Problem
APPLICATIONS
Geogrids
Fatigue Cracking Problem

25. Fatigue Cracking Problem
APPLICATIONS
Geogrids
Fatigue Cracking Problem

26. APPLICATIONS
Geogrids
Road Widening Works

27. GS against Reflective Cracking
0 Not reinforced
1A Nonwoven GT without emulsion
1B Nonwoven GT with emulsion
1C Nonwoven GT impregnated with elastomeric bitumen
2 Polyester geogrids
3 Fiberglass geogrid
4 SAMI
5 Woven GT 5 10 15 20 25 30 35 40 45 3 2 1 4 7 8 1A 1B 1C
Crack propagation (cm)
GS against Reflective Cracking
Loads number (x1000)

29. 4. Drainage arrangement

30. Importance of proper & effective drainage
Undesired water can lead to damage to pavements
The pore water pressure built-up in subgrade may lead to pavement permanent failure
Loss of subgrade support
Reduction of granular layer stiffness

31. Conventional method of drainage
Side trenches are constructed in pavements along the length to drain away the subgrade water
Trenched are filled with gravel

32. Drawbacks of Conventional method
Costlier solution
Difficult to install
As the time pass, the efficiency of drainage reduces due to the clogging of gravel layer
Consumption of natural resources

33. Solution with Geosynthetics
Edge Drain: by Drainage Composite

34. Quantifying the Geosynthetic Benefit
Traffic Benefit Ratio (TBR) (also known as Traffic Improvement Factor or TIF) is a ratio comparing the performance of a pavement cross-section with a geogrid-reinforced base course to a similar cross-section without geogrid reinforcement, based on the number of cycles to failure, with failure defined as a selected depth of rut.
In general, geosynthetics have been found to provide a TBR in the range of 1.5 to 20, depending on the type of geosynthetic, its location in the road, and the testing scenario.

35. Advantages of Geosynthetics in Pavements
Improved service life, lower maintenance
Better drainage arrangement
Improved load carrying capacity
Better load distribution by pavement section
Cost effective if compared to conventional solution
Possible to construct over very weak soil
Reduction on rut depth and cracking
Considerable saving in design thickness
Chemically inactive, non biodegradable material hence high durability

36. INSTALLATION GUIDELINE

37. Installation of Geosynthetics For Separation, Stabilization & Base Reinforcement
1. Subgrade Preparation
- Roadway subgrade preparation typically involves removal of all vegetation, roots, and topsoil.
- Localized soft soil or otherwise unsuitable subgrade areas may be require to be excavated and backfilled with selected materials.

38. 2. Geotextile Placement
- The geotextile is usually laid in the direction of construction traffic
- On very soft subgrade (CBR < 1.0) the fabric layout and aggregate placement should begin on firm soil on the site perimeter.
- The geotextile should not be dragged across the subgrade.
- Wrinkles and folds in the fabric shall be removed by stretching and staking as required.

39. 3. Geotextile Overlap
Rolls of geotextiles must be overlapped, sewn, or jointed as required
Overlap as per FHWA

40. 4. Aggregate Placement
- Construction vehicles should not drive on fabric
- First lift should be placed at minimum 300 mm thick
- Rut depths should be less than 75 mm
- Initial lift should be compacted by tracking-additional lifts with smooth drum vibratory

41. 5. Aggregate Spreading & Compaction

42. INSTALLATION PHASES

43. Effective depth of Road Mesh placement
3 to 6 inches
HMA
HMA
BASE
SUBGRADE

44. Method of deployment for full scale placement
ROADMESH DEPLOYMENT

45. THANKS