Undrained brittleness of sand in triaxial compression and ring shear tests

摘要

Undrained brittleness index, I_B, is defined as the difference between the peak and critical undrained shear strengths normalized by the peak undrained strength, and indicates soil contractiveness and severity of strain softening. In this study, the results of 25 undrained triaxial compression and 20 constant volume ring shear tests performed on two clean sands and one silty sand are used to evaluate I_B. The results illustrate that I_B increases with initial void ratio and state parameter and is affected by particle shape and particle damage, but is independent of the mode of shear (triaxial compression and ring shear). In addition, I_B appears uniquely related to the ratio of consolidation stress to effective stress at critical state, σ'_c/σ'_(cs), and critical strength ratio, s_u(critical)/σ'_c, independent of sand type, mode of shear, initial fabric, and particle damage. These relationships suggest an upper bound critical strength ratio of about 0.3.