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Comparison between Performance of Stone Columns and RAPs from the Bearing Capacity and Settlement Reduction Viewpoints

Golestani Dariani, Ali Akbar | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40894 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. Out of several ground improvement techniques available, stone columns have been widely used. This technique has been successfully applied to increase the bearing capacity and to reduce the settlement for foundation of structures like liquid storage tanks, earthen embankments, raft foundations, etc., where a relatively large settlement is permissible. This technique has, generally, been proven successful in increasing the stiffness of weak soils, upgrading their safe bearing capacity, and reducing their total and differential settlements, as well as speeding up their consolidation process. The beneficial effects of stone column installation in weak deposits is manifested in the form of increased load carrying capacity, significant reduction in total and differential settlements, minimization of the post construction settlements effected by accelerating consolidation, reduction in liquefaction risks, helping in improvement of slope stability of embankments or natural slopes, improving soil behavior under dynamic loads, etc. In this thesis, numerical modeling of construction stages and loading procedure of stone columns are carried out with finite element method, using PLAXIS v. 8.2 software, in order to examine stone column’s performance in different conditions and to compare it with RAP from the bearing capacity enhancement viewpoint. Modeling is conducted in two dimensional axisymmetric form. Since stone columns conduct the duty of drainage of saturated soil, stone column and it’s surrounding soil is modeled in drained condition. For modeling the behavior of stone column and surrounding soil, Mohr-Coulomb model is used and regarding stone column’s installation procedures, the analysis is done in static form. For exact simulation of stone column expansion during construction and considering installation effects in modeling, Cavity Expansion theory is used. Results of numerical modeling of stone column show good agreement with laboratory tests and theoretical methods. Using parametric study, the effect of various factors such as column’s diameter and length, and properties of surrounding soil and stone column, are investigated. The results show stone column’s bearing capacity enhancement when friction angle and stiffness of surrounding soil increase. finally, a comparison between stone column and rammed aggregate pier (RAP) is carried out and the results are presented.
  9. Keywords:
  10. Short Rammed Aggregate Pier ; Pullout Capacity ; Settlement ; Numerical Modeling ; Stone Column

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