1. Research Associate, Faculty of Civil and Environmental Engineering, Chair of Foundation Engineering, Soil and Rock Mechanics, Ruhr Univ. Bochum, 44801 Bochum, Germany (corresponding author).
2. Professor, Civil Engineering Dept., K.N. Toosi Univ. of Technology, 1996715433 Tehran, Iran.
3. Professor, Faculty of Civil and Environmental Engineering, Chair of Foundation Engineering, Soil and Rock Mechanics, Ruhr Univ. Bochum, 44801 Bochum, Germany.