Gennan Long-Term Experience with Reinforced En1bankments on Soft Subsoil: Perfonnance and Durability
Two projects of embankments on soft subsoil with high-strength basement reinforcement are shortly described. Started in 1981 and 1986, respectively they belong to the first one's using preloading plus reinforcement for autobahns and highways in Germany. Site conditions, construction stages, measurement data and eva1uation are presented, including long-term reinforcement strain measurements until 1998. The geotextiles are still under tension. In 1995 high-tenacity polyester woven was exhumed from undemeath the first embankment and analyzed for evaluation of durability. Important results are reported, confirming negligible loss of strength in 14 years. In conclusion, findings and recommendations for focal points of design, long-term reinforcement behavior and durability are summarized.
Two projects of embankments on soft subsoil with high-strength basement reinforcement have been started in Germany in 1981 ('Rübke') and 1986 CGrossenmeer') respectively. The 'Rübke-embankment' is a pure test embankment for the autobahn BAB A 26. The 'Grossenmeer-embankment' is an integral part of the .federal highway B 211. In both cases high-modulus polyester woven is used with 200 kN/m and 400 kN/m UTS, respectively, and 10% ultimate strain. For stability calcula tions DIN 4084 (Bishop's method) has been used, modified by reinforcement force. Meas urement programs are performed up to now, including direct strain measurements at 'Grossenmeer'. Woven from 'Rübke' was exhumed after 14 years under tension below groundwater to evaluate durability.
1. Stability calculations according to DIN 4084 are correct enough to prevent failure of embankment and/or subsoil, at least when high tensile force at low strain is mobilized to restrain deformations.
2. High-moduli for a long period (low creep) are impmiant, because the reinfurcement works after consolidation also. In the projects described it is still under tension after 16 and 12 years, respectively.
3. The high-strength reinforcement used proved to resist overstressing successfully for a long period.
4. Local weaker subsoil zones can easily result in reinforcement overstressing and/or failure tendency; · it should be kept in mind when selecting safety factors.
5. Subsoil squeezing-out is recommended to be checked additionally to DIN 4084- calculations (Bishop) by other methods also.
6. The analyses of durability and Operation conditions indicate in this case, that (internal) hydrolysis under stress in groundwater is the main reason for the registered loss of strength, which is negligible.
7. The loss of strength mentioned above due to 'aging' (environmental effects) is 1.5% to 2% in 14 years for the high-tenacity polyester woven used.