The influence of loading frequency on dynamic soil properties.

摘要

The response of soils to dynamic loads including earthquakes, construction vibrations, traffic vibrations, and storm loads is an important consideration in many design scenarios. This response is primarily determined by the dynamic properties of the soil, i.e., shear modulus and material damping ratio, over a frequency range from about 0.01 to 30 Hz. The objective of this research is to provide for a more complete characterization of the influence of frequency on the dynamic soil properties of clayey soils within this range.; A non-resonance test method was developed to enable measurements of the shear modulus and damping over a broader range of frequencies than is possible with conventional resonant column and torsional shear tests. The observed frequency response function between an applied torque and resulting rotation of the specimen serves as the basis of the test. The accuracy of material damping ratio measurements was improved by developing an electro-mechanical model of the test device that aids in understanding the cause of the equipment-generated damping. The model also led to the design and implementation of a current-mode source to virtually eliminate this problem in real time. The non-resonance test method was validated via comparisons with reference measurements on metal and polymer specimens.; Non-resonance tests were performed on remolded kaolin and natural soil specimens. They reveal important details regarding the frequency dependence of dynamic soil properties that were not apparent in previous data including the existence of inflection points in the shear modulus spectra corresponding to minima in the damping ratio spectra. Test data were interpreted in the context of the Kramers-Kronig relationships for viscoelastic media, which arise from the fundamental principles of linearity and causality. Close agreement was observed between measured and predicted spectra. The results provide considerable insight into the dynamic properties of soils and help to refute common misconceptions about their frequency dependence.