Icon EnvelopeFacebook iconIcon LinkedInIcon Youtube
HUESKER France SAS
Rue Jacques Coulaux
67190 Gresswiller
France
  • Alexiew, Dr.-Ing. D.
  • Blume, Dipl.-Ing. K.-H.

German Long-Term Experience with Reinforced Enbankments on Soft Subsoil: Perfonnance and Durability

Abstract

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.

Conclusion

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.