Abstract: In order to explore the mechanical properties and mechanisms of saturated sands under different normal stresses, shearing rates and pore water pressures, a continuous large displacement shear test was conducted by using a large ring-shear test apparatus. The research results demonstrated that:1) Given continuous fast shearing, the shearing mechanical properties of sands changed differently under dry, non-drainage and drainage conditions. The saturated sands presented certain strain softening under the non-drainage condition. 2) In the ring-shear test with the same positive stress and shearing rate, the shear strengths of the saturated sands differed significantly under the different drainage conditions (upper drainage, down drainage and up-down drainage). 3) Under the drainage conditions in the ring-shear test, the difference between shearing stress and strength of sands was not only related with the fine particle movement and structural changes, but also influenced and controlled by the variations of the pore water pressure in the shearing process. 4) Given drainage ring-shearing, the dissipation of pore water pressure of saturated sands was related with the smoothness of the drainage channels formed in the soil under the different drainage modes, and influenced by different shearing rates and normal stress.

Key words: ring shear test, shear strength, normal stress, shear rate, pore water pressure