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Bearing Capacity and Settlement Analysis of Intermediate Foundation (Short Rammed Aggregate Piers)

Dashtara, Sadegh | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39379 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. Using short rammed aggregate piers (RAP) is one of the ground improvement methods that is suitable for loose sands and soft clays. In this method, gravel or crushed stone is placed in layers with specific thickness in a pre-drilled cavity and each layer is fully compacted with impacts of a hammer. The basic advantages of these piers are increasing soil lateral stresses due to aggregate ramming and increasing the consolidation rate due to high permeability of aggregates. The main application of RAPs is soil improvement underneath shallow foundations, in order to increase the bearing capacity and reduce settlement of foundation. Regarding the usual height of 1.5 to 5m of these piers, a combination of shallow foundation and RAP is called intermediate foundation. In this thesis numerical modeling of construction stages and loading procedure of intermediate foundation are carried out with finite element method by using plaxisv8.2 software, in order to recognize failure mechanism and determine the bearing capacity and immediate settlement of foundation. Regarding symmetry of the geometry and loading condition of isolated piers, modeling is conducted in two dimensional axisymmetric form, and because of high permeability of aggregates, analysis is done in drained condition. For modeling the behaviors of aggregate material and soil an elasto-plastic hardening cap model is used. Ramming energy of hammer is modeled by Applying initial velocity to the nodes as initial condition and then dynamic analysis is conducted. Results of the numerical modelings show good agreement with field measurements in estimation of bearing capacity and settlement. Using parametric study, the effect of different factors such as pier height, ramming energy, and soil resistance on intermediate foundation performance are investigated and based on the results appropriate equations and curves for foundation design are presented. Parametric study results show that height to diameter ratio of the pier is the principle factor for determining failure mechanism of foundation in loose soils. Optimum value of this ratio is around 4
  9. Keywords:
  10. Short Rammed Aggregate Pier ; Bearing Capacity ; Settlement ; Numerical Modeling ; Dynamic Analysis

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