1. ASTM D 5321. Standard Test Method for Determining the Coefficient of Soil and Geosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear Method. American Society for Testing and Materials International, West Conshohocken, PA, USA.
2. ASTM D 6243. Standard Test Method for Determining the Internal and Interface Shear Resistance of Geosynthetic Clay Liner by the Direct Shear Method. American Society for Testing and Materials International, West Conshohocken, PA, USA.
3. Berard , J. F. (1997 ). Evaluation of needle punched geosynthetic clay liners' internal friction.Proceedings, Geosynthetics '97, IFAI, Long Beach, CA,Vol. 1, pp. 351?362.
4. Bressi, G., Zinesi, M., Montanelli, F.& Rimoldi, P. (1995). The slope stability of GCL layers in geosynthetic lining system.Proceedings of the 5th International Symposium on Landfills, Cagliari, Vol. 1, pp. 595?610.