Reza Ziaie-Moayed - Associate Professor, Civil Engineering Department, Imam Khomeini International University, Ghazvin, Iran
Mehrad Kamalzare - PhD, Department of Civil and Environmental Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA

Due to low bearing capacity of soft clayey soils, in places that because of economic, military or geological conditions, we are oblige to build a structure on such soils, geosynthetic will be usedto reinforce the soil and improve the bearing capacity. Particularly, in roads, geosynthetic is placed between the interfaceof granular materials and soft-soil sub grade to improve the bearing capacity of composite layers. In past researches, thebehavior of one layer soils which had been reinforced with different kind of geosynthetic, were studied by experimental and analytical methods and some numerical models have beendeveloped. In this paper the behavior of two layers soils (granular base-clayey sub grade) that have been reinforced with some kindof geosynthetics is investigated. Large scale direct shear tests are performed on reinforced and unreinforced samples with differentgeosynthetics and a comparison has been made between samples with different water contents. The obtained results show that theinclusion of geosynthetics materials improves the shear strength oftwo layered soils. It implies that the geosynthetic-reinforced soils in sub base layer of roads will perform better than non-reinforced ones and therefore, the load carrying capacity of basement is improved.

Shear Strength, Geosynthetic, Large scale direct shear test, Clay, Subgrade