Vibro-Replacement Ground Improvement within Layered and Interbedded Variably Cemented Sedimentary Limestone and Granular Soils

Vibro-compaction or vibro-flotation has been utilized extensively throughout the United States as a means of densification of predominantly granular soils to increase allowable bearing pressures, reduce settlements and mitigate liquefaction. In the coastal areas of South Florida, vibro-compaction has been used predominantly to densify the upper approximately 10 feet (3 m) to 30 feet (9 m) of typically sedimentary, fine- to medium-grained sand to allow support of structures typically less than 15 stories in height on shallow foundations. More recently, vibro-replacement (aka stone columns) has been utilized to provide stiffening or higher modulus gravel/stone column elements into and/or through weakly cemented limestones and densify interbedded or interlayered granular soils. The relative level of cementation or strength of the limestones and constituents of the interbedded and interlayered sands, which exhibit variable levels of carbonate cementation, are key factors in determining the resulting mechanism of ground improvement. Several case histories are presented providing the results of post-treatment testing. The results of full-scale footing load tests and building monitoring to confirm the total and differential settlements throughout the structure are presented as well.