الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Ground improvement using stone columns is one of the most common ground improvement techniques used in soft soils. The design of soil-column-footing systems depends on major simplifications. One of these simplifications is to ignore the effect of stone column installation on enfolding soft soils. Many studies have been performed to examine the real behavior of stone column foundations; however, few studies have investigated the effect of the stone column installation technique on the enfolding soft soil and how to implement this effect on the design procedure, with recommendations for designers.
A validation process was established to examine the ability of Plaxis 2D and 3D to capture the performance of untreated and treated foundations resting on soft soil. The efficiency of the Plaxis solver in capturing the two-load-settlement and load-settlement-time performances of treated and untreated footings was clearly demonstrated. Using the cylindrical cavity expansion method, a comprehensive 2D axisymmetric finite element study was performed to examine the effect of the installation of a single stone column and groups of stone columns on the enfolding natural soft soil. Several expansion degrees—representing different values of radial excitations caused by the vibroflot during installation—were used to quantify the proper and possible values on site.
It was proved that the installation process significantly improves the stiffness of the natural soil, which decreases the treated foundation’s settlement. The installation process also increases the lateral stress parameter (K) for the enfolding soil, which provides more lateral confinement to the stone columns. This lateral confinement resists the bulging that occurs in the top part of the stone columns, which helps the stone columns bear high vertical loads safely. These improvements in the stiffness and lateral stress state of the enfolding soil significantly decrease the resulting settlement beyond the values calculated using common empirical design methods (like Priebe 1995).
The combined use of 2D finite element analysis—for representing the installation process—and 3D FE analysis—for representing real load-settlement behavior—demonstrated great performance compared with field measurements. The findings were validated using two well-instrumented and documented case studies for a wide footing reinforced by a large group of vertically loaded stone columns and an isolated footing reinforced by a small group of vertically loaded stone columns, and the FE outputs were in good agreement with field measurements.
Finally, a parametric study has been conducted and a design procedure was established to simplify the process by which designers consider installation effects on enfolding soft soils in practical design.