Measurement of Strain Rate Effects on Dynamic Soil Properties

摘要

A non-resonance test has been developed to measure the influence of strain rate on the small-strain shear modulus and material damping ratio of fine-grained soils. The test is based on measurements of the frequency response function between the applied harmonic torque and resulting rotation of the specimen. The test also utilizes a voltage-to-current converter to minimize the source-load mismatch and virtually eliminate equipment-generated damping. Non-resonance tests were performed on two undisturbed natural soil specimens to demonstrate the influence of frequency on their dynamic properties. Test data were validated via an approximate form of the Kramers-Kronig relationships for linear viscoelastic media. The test results are provided in the form of detailed shear modulus and material damping ratio spectra and show that the shear modulus does not increase linearly with frequency nor is the damping ratio constant over a broad range of frequencies as is commonly believed.