Seyed Abolhasan Naeini - Associate Professor, Civil Engineering Department, Imam Khomeini International University, Qazvin, Iran
Yashar Hamidzadeh Kalkhoran - Graduate Student, Civil Engineering Department, Imam Khomeini International University, Qazvin, Iran
Amir Saedi Daryan - Assistant Professor, Civil Engineering Department Shahid Beheshti University, tehran, Iran

This paper presents an experimental and numerical study to examine the effect of randomly distributed fiber and scale effects on the shear strength of unsaturated clays. The scrap tire rubbers as reinforcement were randomly included in to the clayey soils with different plasticity indexes at various percent of fiber content (0 to 4%) by weight of raw soils. A series of direct shear tests and also numerical analysis were performed to investigate the strength behaviour of the unreinforced and reinforced samples. The experimental study has clearly shown a significant improvement in the shear strength parameters (C and Ф) of tested soils. Results indicated that with increasing in fiber contents, the reinforcement benefits increased. The finite element simulations for direct shear box tests were performed in the same manner as the experimental tests in order to compare the results of experimental and numerical studies and also, the scale effect on the shear strength behaviour. Three shear box sizes were used in the numerical modelling. The numerical analysis shows the trend of decreasing shear strength with increasing shear box sizes.

Fiber reinforcement, Soil improvement, Direct shear test, Finite element method, Shear strength, Clayey soil, Scale effect