Following Table 2.1 represents the cases where geosynthetics are used as sub-pavement reinforcement. Method of study and major findings from the authors are listed in the table.Table 2.1 Selected case studies of geosynthetics for sub-pavement reinforcementAgency or authors (Year) Subject Method of studyMajor findings

US National Research Council (1988)Pull-out in geosynthetic reinforced baseLaboratory testing - Pull-out is highly variable and depends on geometry, soil density, angle of internal friction, etc.

US National ResearchCouncil, Hass (1988)Geosynthetic-reinforced baseRepeated load tests -Optimum location of reinforcement is at the bottom of base course

US National ResearchCouncil, Barksdale(1989)Geosynthetic-reinforced baseAccelerated pavement tests (primarily with pre-stressedreinforcement)

- Reinforcement reduces deformationor rutting by 2040%- Base course/fill can be reduced by 2550 mm (12 in.) when reinforcement is introduced- Fatigue is reduced whenreinforcement is utilized

Duskov (1997)Reinforcement with geofoamFull-scale/in situ testing of Geofoam Laboratory test using specialized pavement tensile test boxGeofoam is ineffective for pavementReinforcementReinforcing yields favorable results in sub-pavement application

Raymond and Ismail(2003)Optimum location and numberof reinforcement layers-Static and repeatedload testing (lab)- Finite element analysis- Geogrids tested show high peak stress at low displacement, which is good- Ultimate bearing capacity is increased when reinforcement is near the surface (effect diminishes with depth)- Second layer of geosynthetic can be beneficial when introduced at the basecourse-subgrade interface- Finite element analysis can successfully predict behavior of reinforced pavement section

Kamel et al. (2004)Optimum location ofreinforcement- CBR tests (lab)- Static and dynamic triaxial tests (lab)Maximum strength increases at a depth of 7276% (from top)- Modeling successfully predictedsettlement on reinforced section- Geosynthetics at subgrade interfacereduce settlement

Tang et al. (2008)Rutting in reinforcedpavement1/3 scale acceleratedpavement testing- Strength, aperture size, junction strength,and flexural rigidity are most importantin geogrids- Pavement performance ingeogrid-reinforced sections is favorable

Al-Qadi et al. (2011)Effectiveness of geogrids inlow-volume pavements andoptimum placementFull-scale acceleratedpavement testing- Any geogrid improves responseby 2331%- Adding a second reinforcing layer hasonly circumstantial benefits- Geogrid minimizes lateral deformations

Abu-Farsakh and Chen(2011)Investigation of benefits fromgeogrid reinforcementCyclic load testing (lab)Adding a second reinforcing layer hasonly circumstantial benefits- Geogrid minimizes lateral deformations- Pavement performance improvement isproportional to increased tensile modulusof a given geogrid- No clear relationship betweenreinforcement performance and aperturesize of the geogrid- Performance of pavement is optimizedwhen reinforcement is inserted at theupper 1/3 of the base course layer

Table 2.2 given below represents the cases where geosynthetics are used as interlayer reinforcement in pavement. Method of study and major findings from the authors are listed in the table.Table 2.2 Case studies for pavement interlayer reinforcementAgency or authorsTopicMethod of studyMajor findings

US National ResearchCouncil (1989)Benefits of reinforcementinterlayerReview/compilation- Interlayer reinforcement is not recommended based on contractors inexperience and cost analysis

Cleveland et al. (2002)

Geosynthetics inpavement overlays

Crack propagation testsusing overlay tester- In place cost of geosynthetics hadimproved, but economic benefits areonly marginal at the time- Stiffer geosynthet

Button and Lytton(2003)

Guidelines for usinggeosynthetics withHMA overlays

Review of research andrecommendation topractitioners- Includes a discussion on thepotential for treated non-wovengeotextiles as moisture barriers- The in place cost of fabric installationis roughly equivalent to the cost of12?515 mm (0?50?6 in.) of asphalt- Including reinforcement has only6065% success rate- When successful, interlayercontribution is comparable to anadditional 30 mm (1.2 in.) of asphalt

James (2004)

Reinforcement interlayerPresentation- Interlayer reinforcement with geogridsleads to dramatic reduction ofreflective cracking

Shukla and Yin(2004)

Reinforcement interlayerReview- Proper use of geosynthetics couldwaterproof, delay reflective cracking,and improve service life of pavements- Including reinforcement can potentiallydecrease pavements by approx.50 mm (2 in.) for similar performance

Khodaii et al.(2009)

Reflective crackpropagation

Repeated loadtesting (lab)

- Any geogrid inclusion can significantlyenhances performance- Interlayer reinforcement is lesseffective at higher temperatures- Optimum location of reinforcement isat mid-depth of overlay

Virgili et al. (2009) Flexural

strength ofreinforced asphalt

Four-point bendingtests (lab)

- Mathematical methods are able todefine pavement failure points

Correia and Bueno(2011)

Effects of bituminousimpregnation ofgeosynthetics

Lab procedures to measureasphalt retention andstress/strain relation afterimpregnation

- At 0.03% strain, geotextile stiffnesswill increases between 500% and 2230%- Impregnated non-woven geotextileshad permeability comparable togeomembranes (on the orderof

Zamora-Barrazaet al. (2011)

Crack propagation inreinforced interlayers

Repeated load testing- All interlayer reinforcement leads tofavorable results- Interlayer reinforcement withpolypropylene geotextiles can offera 23 times increase in pavementdurability- Geogrid-reinforced pavements showincreased durability and increasedbearing capacity