A geosynthetic has been defined by the AmericanSociety for Testing and Materials (ASTM) Committee D35 on Geosynthetics as aplanar product manufactured from polymeric material used with soil, rock,earth, or other geotechnical engineering related material as an integral partof a man-made project, structure, or system. The geosynthetics that areroutinely used in the transportation industry are geotextiles, geogrids, geomembranes,erosion control blankets and mats, geosynthetic clay liners, geocomposite drainagematerials, and geonets. Those concerned with the analysis, design,installation, and performance of geosynthetics employed in transportationfacilities focus on specifications, design methodologies, constructiontechniques, long-term performance, and economics.


Geosynthetics have been and continue to be usedin all facets of the transportation industry, including roadways, airports,railroads, and waterways. The principal functions performed by geosyntheticsare filtration, drainage, separation, reinforcement, provision of a fluidbarrier, and environmental protection.


Transportation Needs


In designing and maintaining transportationfacilities, designers attempt to provide facilities that will meet userscurrent needs without rapidly becoming obsolete, that will be safe, and thatwill be economical to construct and maintain. In the past, one or more of theseobjectives often had to be sacrificed. Geosynthetics have enabled innovativedesigns that can better meet all of these objectives.


There has been much discussion of the notionthat standardization reduces opportunities for innovation. Another way ofviewing the relationship between the two is to say that innovation, or thestate of the art, must precede the adoption of technology, or its standardization(state of the practice). Quite often, however, the move from state-of-the-arttechnologies to the state of practice within transportation agencies lags behindthat in other engineering communities. Some of this is due to economics; innovationtends to be costly until the technology becomes the standard of practice. Otherfactors, such as governmental conservatism, also play a role. With regard togeosynthetics, designers must become more willing to use these new materials insuch applications as geosynthetic-reinforced earth structures. Doing so willallow the state of the art to become the state of practice, which in turn willlead to reduced project costs.


State Of Practice


Certain geosynthetic materials are usedroutinely by some state transportation departments and local road authorities.These materials and their applications include geotextile roadway pavementseparators, blankets and mats for erosion control, geotextile barrier asphaltoverlays, geosynthetic composite drains, geotextile filters, and geotextile or geogridreinforcement of embankments over soft foundations. The widespread use of geotextileseparators between soft, wet subgrade and base course layers is expected to continue.The use of geosynthetics and synthetic-natural composites for erosion controlis likely to increase in the future with stricter environmental regulations andenforcement.


Impregnated geotextile barriers are usedroutinely in asphalt overlays, but only in certain areas of the country andtypically by local road authorities. Use of these barriers in asphalt overlaysis expected to be limited in the future. Geosynthetic composites are widelyused for pavement edge drains. Expanded use of these drains will likely occuras design and installation procedures continue to be refined, but theirapplication can be significantly increased if more definitive economic benefitsare demonstrated. The use of geotextile filters in drainage systems and ofgeosynthetic reinforcement beneath embankments over weak foundations shouldcontinue in the future.


The future use of geosynthetics in all of theseapplications, particularly asphalt overlays, can be enhanced with betterdocumentation of immediate and life-cycle cost and benefits as compared withalternative methods. Use of geotextile separators over relatively firm subgradecould become routine if the economics and mechanisms of pavement improvementwere better defined.


Design and construction of geogrid orgeotextile-reinforced soil structures are common within some statetransportation agencies. Mechanically stabilized earth wall and, to a morelimited extent, reinforced soil slope structures are now being constructed.Initial cost and benefits have been established, though life-cycle costs havenot been well documented to date. Use of geosynthetic-reinforced mechanicallystablized earth wall and reinforced soil slope structures certainly shouldincrease in the new millennium, although some existing practices may restrictthis growth. Users are continuing to develop better methods and procedures forimplementing these technologies.


 

State Of The Art


Currently, geogrids and geotextiles are being used to a very limited extent to reinforce the pavement base course and to enhance performance over a soft subgrade of flexible pavement structures. These two applications are expected to be more widespread in the new millennium as they become easier for transportation engineers to implement.


However, better definition of mechanistic design procedures, life-cycle costs, key material properties, and specifications is needed for geosynthetic pavement reinforcement to become the state of the practice within transportation agencies. Spurring this expected growth are the challenge of extending the pavement analysis period (i.e. design life) to 30 to 50 years and the growing cost of base course materials.


Another application that should increase is the use of geosynthetics to reinforce fill embankment edges. Reinforcement enhances soil compaction and soil shear strength, thus decreasing future maintenance costs associated with reinstating sloughing-type failures.


Future Directions


Much work will be required to advance geosynthetic applications currently viewed as state of the art and new (as-yet undefined) applications to the state of practice among state and local transportation agencies. The greatest future benefit of geosynthetic materials is likely to be realized in pavement structures. The new millennium is expected to bring definition of the mechanistic contributions of various geosynthetics used within a pavement structure, as well as a clearer valuation of immediate and life-cycle cost and benefits. Furthermore, future pavement design procedures are likely to incorporate geosynthetics for various functions, and perhaps will assume use of geosynthetics for some functions unless clearly eliminated by the design process.


Certainly, new highway applications of geosynthetics will emerge in the future, as will different geosynthetic materials and composites. Products may be developed for enhanced economics and performance of existing applications or for new applications. In addition, applications of geosynthetics will be improved as other technologies are refined. Geosynthetics are well suited to achieving better performance with less-select soil. The versatility and usage of geosynthetics will be enhanced as in situ and rapid soil testing procedures are developed, refined, and implemented by transportation agencies.


Summary


Use of existing, state-of-the-practice geosynthetic applications by transportation agencies should expand in the new millennium with further implementation of life-cycle economics and mechanistic design practices. State-of-the-art geosynthetic applications will be advanced to the state of practice within transportation departments as design procedures and specifications are standardized. New geosynthetic materials and new applications of geosynthetics in transportation are anticipated.


It is expected that the use of geosynthetics will become increasingly routine, and that geosynthetics will be the standard material of choice for several applications. Use of geosynthetics in pavement structures (to perform the functions of separation, filtration, drainage, and reinforcement) should increase significantly in the new millennium as the benefits of these materials are quantified. In addition, the versatility and usage of geosynthetics will be enhanced with the development and adoption of in situ and rapid soil testing procedures.


Originally published in: New Cloth Market, August-2010