A Non-Resonance Method for Measuring Dynamic Soil Properties

A non-resonance (NR) test method is introduced to determine dynamic soil properties at low strain amplitudes over a broad frequency range using a conventional resonant column/torsional shear (RC/TS) apparatus. The theoretical background of the NR method is presented and it is shown that the shear modulus and material damping ratio can be obtained from frequency response measurements between the applied torque and resulting rotational displacement of the specimen. By properly accounting for inertia effects, the NR method allows measurements at frequencies (e.g., 2–30 Hz) that fill the gap between conventional RC and TS tests. Experimental results are presented for aluminum alloy, polymethyl methacrylate (PMMA), and soil specimens over the frequency range of 0.01–30 Hz. Values for aluminum alloy and PMMA, used as calibration materials, obtained with the NR method agree well with reference values from the literature and help validate the approach. Tests on two soil specimens indicate that the NR method permits continuous measurements of shear modulus and material damping ratio of soils over a broad frequency range, which has the potential to yield improved understanding of viscoelastic soil behavior and provide dynamic soil properties over a range of frequencies appropriate for a variety of natural and man-made vibration sources.