ABSTRACT:

Recent experiences with the use of stone columns for settlement reduction at four large international power plant projects are described. Settlements measured from full-scale load tests on triangular and square stone column grids are compared with settlement results for untreated ground and with calculated settlement values. These results are also compared with published data from full-scale load tests and theoretical procedures. Overall, the results from the full-scale tests show more improvement than predicted by theoretical procedures, although a large scatter was observed.

INTRODUCTION

The increasing global demand for electric power generation projects with Òfast-trackÓ schedules requires the use of innovative and cost-effective solutions in all aspects of the projects, including foundations. The use of ground improvement techniques to reduce foundation settlements, in lieu of using piles, often results in lower foundation costs and accelerated construction schedules. Stone column installation is a vibro-replacement technique for ground improvement that consists of replacing existing soil with a gravel (stone) column. This paper provides a general description of an approach used to develop preliminary stone column grid configurations and summarizes the settlement analysis used for four test sites. The subsurface conditions and results of settlement calculations used to determine preliminary grid layouts at the four sites are summarized. Reference is made to other published results, and comparisons and conclusions are drawn. Stone column installation procedures and equipment, and applications other than for settlement reduction, are not discussed, but a good summary can be found in Greenwood and Kirsch (1983). Specialty contractors also provide information that can be very useful.

DETERMINATION OF PRELIMINARY STONE COLUMN GRID CONFIGURATION

A preliminary stone column grid configuration can be selected to yield a target settlement improvement ratio (SIR), defined as the ratio of foundation settlement for original ground conditions to foundation settlement for improved ground conditions.

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