Numerical Methods in Geotechnical Engineering – Schweiger (ed.) © 2006 Taylor & Francis Group, London, ISBN 0-415-40822-9 787 1 INTRODUCTION The Vibro replacement technique is one of the common methods used to install stone columns (stone piles) which are typically intended to reduce settlement and increase bearing capacity of soft soils. Several attempts have taken place to predict the settlement of vibro- replaced soil using numerical modeling. Some of the predictions were in good agreement with field results Kundu et al. (1994), while others indicated that the numerical modeling overestimate the settlement Mitchell and Huber (1985), Ashmawy et al. (2000). These contradictions are attributed to the assumptions involved in settlement prediction, such as the physical and engineering properties of the filling materials and the surrounding soil, and the inaccurate estimation of the diameter of the stone pile. In addition, in the cases where stress dependent stress-strain paths are used for both materials, the coefficient of earth pressure has a great influence on the prediction of settlement. In order to simulate the settlement of vibro replaced soil using numerical models, this paper focused on the estimation of the stone pile diameter by using field results obtained from several projects conducted in Central Florida, and the coefficient of earth pressure of both filling material and surrounding sand using a new application for the hysteretic model and wall movement theory presented by Duncan and Seed (1986) and Fang et al. (1997), respectively. The physical properties of the filling materials in this study were obtained from laboratory tests. The engi- neering properties were estimated from widely-accepted values in earlier papers, mainly because of the difficulty of obtaining an undisturbed sample from both the stone filling material and the surrounding sand, as well as the inability to duplicate in the laboratory the high Tracking the settlement of sand layers stabilized by stone piles using numerical modeling M.F. Mishriki Dept. of Civil and Env. Eng., University of South Florida, Tampa, Florida, U.S.A J.D. Hussin Hayward Baker Inc., Tampa, Florida, U.S.A E.A. Eissa Dept. of Geology and Geophysical Eng., Suez Canal University, Suez, Egypt S.I. Shalaby Dept. of Geol. and Geoph. Eng., Suez Canal University, Suez, Egypt A.K. Ashmawy Dept. of Civil and Env. Eng., University of South Florida, Tampa, Florida, U.S.A ABSTRACT: Several field plate load tests were performed on soft soils stabilized by stone piles installed using the vibro replacement technique in Southeastern United States. In order to simulate field settlement using finite elements, the actual stone pile diameter has been established using different techniques. The study showed that the diameter of the stone pile was tapered from a maximum value at the surface to a minimum value at a certain depth. By dividing the vibro replaced soil into several layers, the diameter of the stone pile was established by assuming that the dry density of the first layer had reached its maximum value. Also the coeffi- cient of earth pressure for both the filling material and surrounding soil were obtained based on the hysteretic model presented By Duncan (1983) and the wall movement theory presented by Fang (1997), respectively. Using these estimated column diameter and coefficient of earth pressure in constructing the numerical model showed a good agreement between the predicted settlement and the measured settlement. Copyright © 2006 Taylor & Francis Group plc, London, UK