| Over the past 20 years many millions of dollars have been spent in remediation of soils prone to the devastating consequences of liquefaction. In North America, approximately 150 sites have been remediated by densification, hardening, or drainage methods. The construction technique known as vibro-replacement or vibro-displacement, referred to in this dissertation as vibro-stone columns, densifies granular soils while installing a stone column which is relatively more permeable and stiffer than the surrounding soils. Prior to this research effort, estimation of post-treatment densification had been based primarily on engineers, contractors experience, and/or site specific test sections. Furthermore, a lack of knowledge on drainage and stiffness parameters of the installed stone columns, had prevented these properties from being included in remediation designs. Nonplastic silts could only be improved by expensive techniques such insitu replacement, excavation and replacement, mixing, or dewatering.;This research significantly advances the state of knowledge by evaluating the vibro-stone columns mechanisms of densification, development of formulae permitting prediction of densification in terms of SPT and CPT field tests for differing soil conditions, evaluating stone column drainage parameters and response in the field and laboratory, and developing a mathematical model capable of modeling earthquake shear stress redistribution. These contributions have been incorporated into a design method which allows practicing engineers to design vibro-stone columns for the prevention of liquefaction in soils ranging from clean sands to nonplastic silts. The method is loosely coupled so, depending on soil type and site conditions, single or combined criteria can be applied to a design problem. Similarly, one criterion may be more influential than the others. For instance, in the case of low permeability silt soils not densifiable by the action of vibrations from the installation of the stone column, the criterion of shear stress redistribution will control the design. Application of this research leads to a widening of spaces between stone columns, or reduction of stone column diameter, which in turn, will provide significant cost savings of liquefaction remediation programs. |
