Ali Ramazan Borujerdi - Graduate Ressarch Student, Department of Civil Engineering. Qom University of Technology, Qom, Iran
Morteza Jiryaci Sharahi - Assistant Professor, Department of Civil Engineering, Qom University of Technology, Qom, Iran
Masoud Amelsakhi - Assistant Professor, Department of Civil Engineering, Qom University of Technology, Qom, Iran

The direct shear test and triaxial test were conducted on specimens with ۰, ۱۰, ۲۰, and ۳۰% clay contents under ۵۰, ۱۰۰, and ۱۵۰ kPa overloads to investigate the effect of fine-grained on the strength of the sandy soil. Preparing the specimens requires determining the maximum dry unit weight and the optimum water content of the soil. Therefore, before conducting the main tests, a series of proctor compaction tests were performed on the soil specimens. The tests were conducted on clean sand and a mixture of sand and clay. The results of the triaxial test showed that the ultimate strength and failure strain increase by adding to the clay content to the specimens. Moreover, adding clay increases the residual strength of soil. Compared to the results of direct shear tests, the stress-strain behavior of specimens is dominated by the clay content as it increases the stiffness of the sand-clay mixture.

Triaxial Test, Direct Shear Test, Clay Soil, Sandy Soil