Effect of geogrids on low volume flexible pavements case study

1. EFFECT OF GEOGRIDS IN LOW
VOLUME FLEXIBLE PAVEMENTS
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2. CONTENTS
 1. What is Geogrid
 2. Different types of geogrids
 3. Flexible pavement distresses
 4. Low volume flexible pavements
 5. Effect of geogrids in low volume flexible pavements : A case study
 6. Conclusions
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3. GEOGRIDS
 A geogrid is geosynthetic material used to reinforce soils and similar
materials
 First known soil reinforcement dates backs to the
6th century BC when the Mesopotamians used
woven reed mats to reinforce the clay in order
to construct their Ziggurat structures
ziggurat
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4. TYPES OF GEOGRIDS
 1. Micro grid
 2. Strata grid
 3. Uniaxial geogrid
 4. Biaxial geogrid
 5. Multilayer geogrid
 6. Welded strip geogrid
 7. Wrap knitted polyester geogrid
 8. Fiber glass geogrid
 9. Steel plastic composites geogrid
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5. APPLICATIONS OF GEOGRIDS
 Soil reinforcement
Roads constructed on poor sub-grade soil requires a larger thickness of
pavement which can be reduced by inclusion of Geo-grid.
Increases the bearing capacity of the sub-grade.
Reduce the differential settlement of the pavement
Increases the life of the pavement
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6. FLEXIBLE PAVEMENT
 The component of a typical flexible pavement structure from the
bottom to top consist of
 1. Prepared soil subgrade
 2. Granular sub-base cum drainage layer
 3. Granular base course
 4. Bituminous binder and surface course
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7.  The top layer of the pavement has to bear the highest magnitude of stresses
and wear and tear due to moving traffic loads. Hence it must be composed
of good quality materials
 The soil subgrade is a layer of natural or selected soil from identified
borrow pits fulfilling the specified requirements and well compacted in
layers to the desired density to required thickness.
 The subgrade layer is the lowest layer of the pavement layer system which
ultimately supports all other pavement component layers and the traffic
load.
 So the strength of the subgrade is an essential part of making quality
flexible pavements and it is scientifically proven that geogrid
reinforcement improves the performance of the subgrade in many ways.
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8. PAVEMENT DISTRESSES
 In a well-designed or constructed flexible pavement, elastic
deformation(deformation due to applied load would be fully recoverable when
the load is released) is expected to take place due to repeated application of the
wheel loads
 Permanent deformation or plastic deformation may also occur at different
situations
 The accumulated permanent or non-recoverable deformation of the subgrade
along the wheel paths of heavy vehicles results in the formation of longitudinal
‘ruts’
 Application of geogrids is found to improve performance against rutting
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10. LOW VOLUME FLEXIBLE PAVEMENT
 The average daily traffic of these roads are generally low and the
total standard equivalent axle loads (ESAL) during a design life of
ten years would be less than 1 million standard axles. Such roads are
generally classified as low-volume roads.
 It is important that this low volume roads which provide
connectivity to these small villages are also planned, designed and
constructed as “all-weather roads” so that these villages are not cut
off during certain periods of the year during the monsoon season
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11. APPLICATION OF GEOGRID IN LOW VOLUME
FLEXIBLE PAVEMENT:CASE STUDY
 The case study is based on research conducted by University of Illinois Advanced
Transportation Research and Engineering Laboratory (ATREL).
 9 Low volume pavement design sections of low CBR of 4%
 Total 173 pavement embedded instruments to measure responses
 The instruments for response collection includes
 Pressure cells
 Strain gages
 TDR(Time domain reflectometry probes)
 LVDT
 Piezometers
 Thermocouples
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12.  Loading
Moving tire load controlled by in-house accelerated loading facility
PAVEMENT CONSTRUCTION
9 pavement sections are divided into 3 categories (Cells) based on total thickness of the
section
Cell A : 203 mm of aggregate base and 76 mm of HMA , i.e. Thin base pavement
Cell B/C : Two HMA thicknesses, 76 and 127 mm, placed over a 305-mm aggregate
base, i.e. intermediate base layer
Cell D : The HMA is 76mmthick placed overa457-mm base layer, i.e. Thick base
pavement
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13. 13

14.  Geogrids are placed at the base-subgrade interface, but in cell D it is
also placed with in the base
 All sections are 6.1m long &3.6m wide, except B2 & C1 which are
7.6m long & 3.6m wide
 The geogrid used is biaxial type
 2 type of geogrid were used in A1 & A2
 At D2 two layers of geogrid were used
 Location of instruments
 Load associated instruments are placed at the centre line of each section
 Environmental instruments at 0.9m offset
 LVDTs are placed in 2 directions one to measure
horizontal(longitudinal,transverse)movement&other vertical deflections
 All instruments are connected to DAQ system
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15. Locations of instruments 15

16. Depth of instruments measured from top surface of the layer
Layer HMA Base Subgrade
Instrument Strain gauge LVDT LVDT
Section Transverse Horizontal Vertical Longitudinal Transverse Vertical Pressure cell
A1
A2
A3
B1
B2
C1
D1
D2
D3
76
76 76
76
76
76 76
76
76
76 76
76
200 200
200 200
200 200
305 305 305
305 305 305
305 305 305
457 457 457
153,457 153,457 153,457
153,457 153,457 153,457
153 0
153 0
153 0
153 0
153 0
153 0
153 0
153 0
153 0
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17. Experimental program & Loading
 Loading was done using ATLAS
 Loaded using dual-tire assembly
 ATLAS has a loading length of 26 m
 Unidirectional loading
 Loading was conducted at centerline and at 3 offsets 152,305,4567mm
 Response is tested for different loading criteria(Tire load, Tire configuration, Tire
pressure, speed)
 Response data collection
 Two category of data viz. Dynamic(load based eg.pressure,Strain,Deflection) &
Static(Environmental.eg.Temperature,Moisture)
 DAQ system monitor this &stores data in excel format file.
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18. Results and analysis
 1.Effect of offset
Thin base pavements are having more response
exception of thin-base pavement, the maximum responses of pressure cells and
LVDTs were recorded in between the dual tires
2.Effect of load
The lowest pressures were exhibited at the double reinforcement section (D2)
and the thick HMA section (C1)
The unreinforced (B1) section showed higher subgrade deflections than the
reinforced B2 section.
3.Effect of speed
The higher the speed, the lower the tire’s effect on pavement.
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19. Effect of tire offset on subgrade pressure
Effect of tire loading
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20. Effect of tire inflation pressure
As the tire pressure decreases, the tire contact area increases; hence, the
response on the pavement decreases
Effect of base layer thickness and geogrid
 Increasing the base layer thickness by 50% enhances the stability of the pavement thus
increases service life
 Reinforced sections showed least response(Excluding thin base pavements and thick HMA
sections)
 Thick HMA section showed less response even though geogrid was not present
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21. Effect of speed
Effect of base layer thickness & Geogrid
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22. Effectiveness and optimal locations for geogrid
Reinforcement Index(RI)
RI = (Pavement response/pavement depth )*100%
Bold letters indicate reinforced section
Response 203 mm base
A1 A2 A3
305mm base
B1 B2 C1
457 mm base
D1 D2 D3
Base transverse strain 0.12 0.14 0.16 0.06 0.05 0.01 0.02 0.01 0.09
Base longitudinal strain 0.16 0.17 0.25 0.09 0.07 0.01 0.02 0.02 0.06
Subgrade vertical
deflection
0.6 0.83 0.8 0.2 0.09 0.04 0.07 0.06 0.05
Subgrade vertical pressure 13.42 15.68 14.85 8.24 9.34 4.26 4.35 3.84 4.81
HMA transverse strain 451.38 513.8 314.15 267.75 207.53 16.59 79.18 84.66 107.97
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23. The reinforced section(s) in each cell have performed better than the counterpart control sections.
C1 has the least pavement responses as a result of the lowest RI values
Increase in base thickness by 50% reduced the responses by an average of 50%
For unreinforced sections (B1–C1 and D3), increasing HMA layer thickness by 51 mm (from B1 to C1) is
more effective than increasing the base layer by 152 mm (from B1 to D3).
Effect of geogrid is more prominent when installed in thick-base layers.
Geogrid has improved performance by 45, 28, and 22% for cells D, B/C, and A, respectively
In cells A and B/C, the improvement in pavement responses as a result of reinforcement implied that the base–
subgrade interface is an effective location for geogrid.
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24.  Geogrid placement at one-third of the base layer thickness is equivalent to the
placement at both the bottom and one-third of the base layer thickness(D1&D2)
 For pavement layers with a 300-mm base thickness or less, increasing HMA
thickness will be more effective than geogrid.
 Performance against rutting
 Rutting occurs due to continuous vehicular testing
 Rate of rutting is defined as the ratio of rutting depth to no. of passes
 It was found that Rate of rutting depended upon the structural design and
geogrid reinforcement
 C1 had the lowest rutting
 Reinforced sections marked a reduction of 43, 25, and 20% in the rutting with
respect to their adjacent control ones
 The double reinforcement doesn’t contribute to rutting resistance
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25. Performance against rutting: surface profile in longitudinal direction
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26. CONCLUSIONS
 Geogrids are of so many types based on their properties and geometry
 Geogrids are cost effective that is they are economic in applying in road sections
 Geogrids are strong in resisting tensile forces
 From the experiment done in Advanced Transportation Research and Engineering
Laboratory (ATREL) at university of Illinois the effectiveness of geogrids in subgrade
soil in low volume flexible pavement was proved to be right
 Various responses measured by the devices indicated that the section that was
reinforced with geo grids was superior with respect to other section in resisting the
damages
 Rutting was very efficiently resisted by the pavement section which was reinforced
with geogrids
 Effect of geogrid is more prominent when installed in thick-base layers.
 Base- subgrade interface is an effective location for geogrid placement.
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