EFFECTS OF PLASTICITY AND SAMPLE DISTURBANCE ON STATISTICAL PROPERTIES OF UNDRAINED SHEAR STRENGTH

抄録

Statistical properties of undrained shear strength c_u are investigated through laboratory and in-situ tests. In laboratory, a series of unconfined compression tests and triaxial UU tests are performed using mixed soil samples. Concerning in-situ soil samples, comparative study is made between disturbed and undisturbed soil specimens. Following findings and method are obtained : (1) When plasticity index I_p is greater than 15%, the difference of c_u between unconfined compression test and triaxial UU test is less than 2% and is almost negligible. However, when I_p is smaller than 15%, unconfined compression test always provides smaller strength than triaxial UU test. c_u of unconfined compression test is about 15% smaller than that of triaxial UU test when I_p≒10. (2) Concerning the coefficient of variation of strength V(c_u), however, there is no significant difference between these two testing methods. Moreover, V(c_u) is found almost independent of both plasticity index and consolidation pressure. (3) When soil specimens are disturbed, the mean value of q_u becomes small while the coefficient of variation becomes large. In the case of E₅₀, however, the coefficient of variation holds constant during disturbance procedure. (4) The method of predicting statistical values of strength of undisturbed specimens from those of disturbed samples is newly presented.