Direct and Indirect Local Deformations of Sand in Undrained Cyclic Triaxial Tests by Image Analysis Technique

A series of undrained cyclic triaxial liquefaction tests were conducted to observe directly and indirectly the local deformations of sand specimen through a transparent membrane. Black-colored silica sand, mixed in white-colored silica sand, was used for the direct evaluation. Black-colored dots, used for observing the local deformations indirectly, were pasted on membrane with a constant interval of 5 mm. Digital photographs were taken in front of the triaxial cell to evaluate the deformations of sand particles patterns and dots by Particle image Velocimetry method. The results indicated that image analysis is an efficient method for direct and indirect measurements of local deformation. Comparison of direct and indirect evaluations revealed that relative movement between sand particles pattern and an adjacent dot on the membrane had a leap when excess pore water pressure ratio reached unity.