Loading...

Investigation of Dynamic Response of Shallow Foundations on Layered Soil Medium by Physical Modeling

Mousavi, Mohammad | 2011

984 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42185 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. Dynamic impedance functions method is most recent approach in the analysis of soil-foundation dynamic interaction, and presented for massless rigid foundations. Impedance functions are frequency dependent functions, and used to obtain dynamic response of foundation with arbitrary mass subjected to dynamic loading of any frequency and magnitude. The important assumptions for appropriate useof mentioned method are rigidity of foundation and visco-elastic behavior of the soil beneath the foundation. In this study, experimental vertical impedance functions of square and circular foundations have been investigated,using physical modeling tests. A granular soil layer with finite thickness underlain by bedrock was selected as the soil profile beneath the foundation. The tests were carried out inside a steel container of dimensions 1×1×0.8m in length, width and height respectively. Babolsar sand was poured into the container, using air-pluviation technique, to reconstitute the soil layers with different thicknesses and constant relative density of 55 percent. Concrete slabs were inserted under the soilto simulate bedrock in the tests. Also, to avoid stress waves reflection from the side of the container, a sawdust layer of thickness 10cm was used to surround the soil before the sand raining operation. Square and circular model foundations were made of concrete, with same equivalent radius equal to 7.5cm. Physical modelswere subjected to forced vertical harmonic vibration during tests by an electro-magnetic shaker, and dynamic response and impedance functions of physical models were measured and calculated by the accelerometers and force transducer, installed on the foundation and inside the soil medium. Results show that the presence of a rigid layer under the soil layer, even in deeper elevations, affects critically the dynamic response and impedance functions of the foundation, and causes several resonance frequencies. Damping coefficient increases by increasing soil layer thickness, however dynamic stiffness, despite the same trend for all soil layers, depends entirely on three dimensional stress waves propagation and their interaction in the soil medium. In smaller frequencies, the equivalent radius concept yields sufficiently precise solutions, but in higher frequencies, impedance functions of square and circular foundations, with same equivalent radius, are relatively different.In addition, results show that impedance functions, especially in higher frequencies, depend nonlinearly on the magnitude of the static interface stress. First resonance frequency and its amplitude increased by increasing soil layer thickness, static interface stress, and magnitude of harmonic loading. Also, the first resonance frequency and amplitude of square foundations are smaller and larger than circular modelsrespectively.
  9. Keywords:
  10. Physical Modeling ; Impedance Function ; Vertical Foundation Vibration ; Finite Thickness Soil Layer ; Bed Rock

 Digital Object List

 Bookmark