Importance of Measuring Local Strains in Cyclic Triaxial Tests on Granular Materials

Deformation properties of sand and gravel were evaluated by cyclic loading (CL) triaxial tests and monotonic loading (ML) triaxial compression tests using small and large triaxial apparatuses. The results were compared with those from other testing methods. The specimens had non-lubricated regular ends. Two types of local gages set on the lateral surface of specimen measured local axial and radial strains. A load cell was located inside the triaxial cell. For a strain range from about 0.0001 % to about 1 %, axial strains measured at the specimen cap in the both ML and CL triaxial tests and damping in the CL triaxial tests tend to be much larger than those measured locally due to bedding errors at the top and bottom ends of specimen. Stiffness values from static CL tests (i.e., very low frequency CL tests) and resonant-column tests (i.e., very high frequency CL tests) were nearly the same, showing that the deformation properties during CL at strains of 0.0001∼ 0.1 % can be obtained only by static CL tests. Stiffness values at strains less than about 0.001 % were practically the same among static ML and CL tests and dynamic CL tests, and between triaxial and torsional shear tests, whereas the dependency of stiffness on strain level is different among them.