Effect of slenderness ratio of the specimen on resonant column test results

To investigate the effect of the slenderness ratio (L/d) of the specimen, resonant column (RC) tests were conducted on dry sand specimens by using three different values of L/d, namely 2, 3, and 4, keeping the same diameter (d = 50 mm) to measure the shear moduli and material damping associated with the shear strain varying approximately from 0.0004 to 0.03 %. For the sake of the comparison, bender element (BE) tests were also performed on the same specimens to examine the effect of L/d on the shear moduli. Different combinations of relative densities and isotropic confining pressures were employed. The current experimental findings based on the simplified theory, which is widely used for analyzing the RC test results, reveal that the measured shear moduli of the specimens become higher for a slender specimen. On the other hand, the damping values were found to be only marginally affected with the changes in L/d. For greater L/d, generally the damping values were found to be slightly higher, especially with greater relative densities. The BE tests, on the other hand, hardly illustrate any variation in shear moduli with the changes in L/d. The shear wave velocities (Vs) from the BE tests were found to be a little greater as compared with the RC tests, and the difference between two sets of results becomes narrower with an increase in L/d. This study reveals that it will be more appropriate to use a L/d equal to 4 rather than 2, especially when testing at isotropic confining pressure ≥ 500 kPa