Geosynthetic reinforcement of roads

Earlier the use of geosynthetic fabrics was discussed for bridging voids and tali that form when ice-rich permafrost degrades beneath a road or airport embankment. Geosynthetics have also been used to reinforce the embankment against lateral spreading which results in longitudinal tensile cracking. The practice of repairing longitudinal cracks is described as a "dump and run" procedure in which the crack is covered with asphalt paving material to bridge

the crack and to level the road. The associated void in the embankment below the pavement is simply bridged by the repair but not filled. The crack continues to grow through several surface repairs until the under pavement void is dangerously wide and the road must be rebuilt. Kinney (1986) used a high modulus polyester material to reinforce the embankment against lateral spreading. In full scale embankment tests using trucks weighing from 4,900 to 21,400 lb_m to load the embankment, it was found that the geosynthetic was able to span cracks up to two feet in width while maintaining acceptable vertical deformation in the asphalt paved surface (Kinney and Savage 1989).

Reflection cracking has also been addressed with geosynthetic fabrics. It appears in asphalt pavements above the cracks that develop in the embankment below due to spreading and or thermal contraction. Sherman (1982) reports that the results have been mixed. The best results came from two sections that used a non-woven polypropylene material. Reflection cracking in these sections was reduced to 5% as compared to 70% in the control sections after 5 years.

In Alaska results have also been mixed. Geotextile overlay on the Gustavus airport reduced the cracking from 40% in the non-reinforced repair to 10% in areas reinforced with a non-woven polyester geotextile after 4 years. On the other hand a test section was installed by the Corps of Engineers on Elmendorf Air Force Base using a woven polypropylene cloth bonded to a layer of adhesive rubberized asphalt In this test 100% of the primary cracks had reflected through after just one year, and 95% of the secondary cracks were again present after 3 years (Johnson 1984).

One of the most widely accepted uses of geotextiles is in separation of coarse grained granular materials from adjacent layers of fines. Intrusion of the fines into the coarse grained material destroys the non-frost-susceptibility of the coarse grained layers. Proper use of the correct geotextiles can reduce or eliminate this effect and protect the coarse grained portion of the embankment from frost-heaving action. This benefit is most notable on low-volume roads in

which very thin gravel fills are commonly used.

The use of fabric layers in embankment design and construction is a new and active field with superior new products being introduced constantly. Design procedures are still in the formative stage, as we learn how to make the best use of this emerging technology.

Words and expressions:

Reinforcement Укрепление

Fabric Сооружение

Void Пустота

Tali Откос, скат

Crack Трещина

Pavement Дорожное покрытие

Intrusion Внедрение

To introduce Применять

Список литературы:

1. A.C. Housby “Winter roads”, 2000

2. James E. Clyde “Drainage requirements”, 2002

3. Terry T. Fadden and Lawrence Bennet “Construction in cold regions: a guide for planners and engineers”, 1996

4. Patrick Powers “Reinforcement roads”, 1998

5. Austin Barry “Construction measurements”, 1998