Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Civil, Construction, and Environmental Engineering

First Advisor

David J. White


This dissertation is a compilation of four papers submitted to scholarly geotechnical engineering journals. Each paper includes references to literature reviewed, research data, and significant findings. The first paper presents an experimental study performed to investigate the influence of induced lateral stress on shear strength, vertical stiffness, and preconsolidation pressure of the reconstituted Iowa loess. Four series of stress path control tests were conducted in which soil specimens remolded from western Iowa loess, were consolidated under increased lateral stress before being loaded vertically in either drained or undrained fashion. The second paper describes a numerical analysis using an axisymmetric, finite element model to study the behavior of isolated rammed aggregate piers subjected to compressive load. The load transfer mechanism along pier shaft and pier-soil interactions is particularly investigated in this paper. Constitutive parameters of the materials involved in the numerical analysis were determined from in-situ and laboratory tests. The finite element model was validated by comparing the numerical results with the data obtained from full-scale, instrumented load tests. The third paper presents results from full-scale, instrumented load tests conducted on two trial square pier-supported footings and three isolated rammed aggregate piers. Group effects are investigated by comparing the behavior of an individual pier within the pier group and an isolated pier from the same diameter and length. Evaluation of the current design methods for computing bearing capacity of pier-supported footing is carried out by comparing the calculated parameters with the measured values. The fourth paper presents a numerical study on the support mechanism of rammed aggregate pier groups. The numerical study focuses on the group behavior of rammed aggregate piers and the vertical stress distribution underneath the footings. A modulus-based method developed based on the homogenization approach combined with the finite element stress distribution for estimating footing settlement is also presented in this paper.



Digital Repository @ Iowa State University,

Copyright Owner

Ha Thuc Van Pham



Proquest ID


File Format


File Size

210 pages