Advancements in resonant column testing of soils using random vibration techniques

This study focuses on advancements in resonant column testing of soil and rock using random vibration techniques. A large free-free resonant column device was built and modified to enable the direct measurement of rotational transfer functions of soil specimens in the frequency domain. Theoretical rotational transfer functions and strain measures were derived and programmed for the new approach. Random (white noise) and swept-sine excitation types were used to vibrate soil specimens over a range of strain levels, confining pressures, and frequencies, while rotational accelerations of the end platens were measured. Shear modulus and damping were then determined by fitting the measured peak frequencies and amplitudes by theoretical rotational transfer functions. Nonlinear strain-dependent modulus and damping curves were generated by measurement of the multi-modal vibration response over a range of excitation intensities. To provide a preliminary validation, results for the new technique are evaluated against those from the current ASTM Standard D4015 for the same soil specimens. Results were found to compare well in terms of maximum shear modulus as a function of confining pressure. The nonlinear strain-dependent modulus reduction and damping curves were found to be similar in shape, but have different values of shear strain, possibly due to the need to account for strain energy at all frequencies in the broadband transfer function tests.