According to Barton-Bandis joint peak shear strength criterion

relationship between peak shear displacement and normal stress is analyzed; and the limitations of Barton’s formula of peak shear displacement are summarized. It is verified through direct shear tests in which joint roughness and normal stress are the two major factors influencing joint shear displacement. The results show that there is a negative relationship between peak shear displacement and joint roughness but a positive relationship between peak shear displacement and normal stress. A new formula is suggested which can consider not only joint roughness but also normal stress and can overcome the limitation of Barton’s empirical formula which just considers joint roughness. The validity of proposed formula is verified through fitting experimental data.