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Radial preloading for ground improvement.
Thesis information
Author:
Biringen, Emre.;Advisor(s):
Edil, Tuncer B.Degree:
Ph.D.School:
The University of Wisconsin - Madison.Year:
2006Full Abstract
A new technology for soft ground improvement, called Preload(TM) Pier, has been proposed for limiting vertical settlements. These piers are inserted in the ground and expanded about three times their original cross-sectional area. As a result of this expansion, the surrounding soil is radially stressed, which initiates consolidation and general stiffening. The end result is a pier-soil composite with enhanced stiffness and strength to support foundation or embankment loads within tolerable settlement.;This technique can be viewed as a cavity expansion problem for which there are reliable finite element method solutions. These solutions provide stress changes at increasing radial distances from the center of the expanding cavity (e.g. driven pier or Preload Pier). However, the resulting changes in vertical stiffness have not been explored. The objective of this research is to address this specific issue through laboratory experiments and numerical modeling. The improvement in the vertical settlement and stiffness (i.e., shear wave velocity) of the clay surrounding the pier was demonstrated in a laboratory experiment. A numerical model, following the cavity expansion theory, was verified in terms of the experimental results. The results indicate that most improvement in modulus and strength takes place within a distance of 4-6 times the radius of a pier.;A parametric study of the in-situ Preload Pier application based on the verified numerical modeling approach was undertaken. The parametric study illustrated that the radial zone of influence due to preload pier (which can be viewed as half pier spacing) in the surrounding soil increases with increasing initial soil stiffness and with final radius of expanded pier. The ratio of radial zone of influence to final pier radius, which remains constant irrespective of the final radius of expanded pier, is approximately equal to 3.5 for soft clay and 6.5 for medium stiff clay. The maximum reduction in vertical settlement in the surrounding soil, depending on the magnitude of the applied vertical pressure, ranges from 10 to 35 percent.
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