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Investigation of Dynamic Response of Shallow Foundations on Layered Soils to Horizontal Harmonic Loading by Physical Model Tests

Ashoori, Taha | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43684 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. Increasing requirements of industries and research institutes to analytical results of interaction soil-foundation related systems, reveals the importance of the dynamic impedance functions than ever before. The dynamic impedance function relations are presented for massless rigid foundations which is possible to obtain dynamic response of foundations for different frequencies and masses accordingly. In this study, the dynamic impedance functions were investigated using physical modeling tests on sandy soil with finite thickness soil stratum over bedrock. The tests were carried out inside a steel container of dimensions 110.8m in length, width and height respectively which was filled into container with babolsar sand by using air – pluviation technique after calibration test with relative density of 55.1 percent. A 10cm thickness saw dust was employed between container and sand to simulate infinite half space and remove stress wave reflection due to foundation vibration from the side of container. Concrete slabs of 15cm thickness also were applied to simulate the bedrock beneath the sandy layer. The selected foundations were square and circular with same surface area and rectangular with length to width ratio of 2 that were investigated to determine effects of shape, inertia, embedment ratio, dynamic force amplitude and bedrock on horizontal impedance.Bedrock generally affects the impedance function. This effect in particular after dimensionless frequencies of 2.5 shows dramatic increase in all three foundation model tests. Dynamic stiffness and damping coefficient increase with increasing embedment ratio. The dynamic response of square and circular foundations is different to some extent due to wave propagation which is dependant to foundation geometry and confirms the small effect of equivalent radius in subject of shallow foundations dynamic response. Mass increase is ineffective on impedance function between dimensionless frequencies of 0 to 2.5 in square foundations and 0 to 5 in rectangular foundations. So the massless foundation theory is not extensible to foundations with variable geometry dimensions. Dynamic force amplitude increase generally does not considerable influence the foundations stiffness and damping coefficients and just causes local resonance displacement through the system response. Soil layer thickness reduction, increase the soil dynamic stiffness.

  9. Keywords:
  10. Shallow Footing ; Bed Rock ; Physical Modeling ; Dynamic Stiffness ; Damping Factor ; Impedance Function ; Harmonic Loading

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