Abstract: In order to analyze the flow deformation of sand under zero effective stress and shearing condition, traditional ring-shear apparatus is modified with the transparent box for specimen visualization. By analyzing the expansion of transparent box and comparing the shear tests of standard sand, the rationality of the ring-shear apparatus after the reformation is validated. By analyzing the shear stress-strain curves of saturated suspension plastic sand under unconsolidated undrained condition, strain softening is found in the shear strength. And by analyzing the effective stress of saturated suspended plastic sand, it is proved that the saturated suspended plastic sand in the visual ring shear tests is in zero effective stress state. The results show that the shear deformation of the saturated suspended plastic sand under the consolidated undrained condition is obviously discontinuous. Fracture occurs directly on the shear plane. The shear deformation of the saturated suspended plastic sand under unconsolidated undrained condition has distinct flow characteristics. The deformation characteristics are related to the shear rate. Under the low shearing rate, the shear flow deformation only forms on the shear plane and shows curved trajectory. But under the high shear rate, the shear flow deformation is totally incline, and consistent with the flow deformation of viscous fluid.

Key words: zero effective stress, visualized ring shear tests, saturated suspended plastic sand, flow deformation, shear rate