Drilled Shaft Foundation Solution at a Challenging, Variable Karst Site in Tampa

摘要

Since 2016, a developer in Tampa, Florida, has been involved in a major facility expansion, which includes new parking garages, an elevated Porte Cochere, a central utility plant, a three-story low-rise expansion, and a new 17-story hotel tower. Constructing the expansion structures while maintaining an operational facility presented its own set of unique complications. Because of numerous geotechnical challenges, extensive coordination was required among the design team, ownership, specialty subcontractors, and general contractor to meet the rigorous project demands. The challenging subsurface conditions included highly variable strength characteristics typical of the underlying Tampa limestone formation, karst features within the formation, and the potential for destabilization of the working platform by construction-induced subsidence related to the selected foundation or ground-improvement system installation. All these factors needed to be considered and implemented with regard to potential impacts to adjacent structures supported on a variety of foundation systems. Geologic anomalies such as zones of highly atypical depths to the limestone bearing stratum and interbedded zones of variable infill materials were also encountered. These conditions required specialized construction techniques and a highly skilled team working together. To accomplish the project goals, a number of geotechnical solutions were used including drilled shafts, augered cast-in-place (ACIP) piles, micropiles, vibro-replacement stone columns, and low-mobility grouting as well as deep soil-mixing, tiebacks, and chemical-grout stabilization for support of excavation. To effectively implement a wide range of foundation and ground-improvement solutions, an extensive subsurface investigation was performed followed by comprehensive load testing. Production-phase non-destructive testing for each of the various foundation components was included along with supplemental load testing. An overview of the development concept and a description of each of the geotechnical challenges encountered, the approaches formulated, and subsequent use of each solution is presented here. Additionally, load-test results for drilled shafts will be compared to load-test data from other parts of the Tampa Bay region to highlight the complexity of the project. Non-destructive test results will validate the specialized construction techniques that were required. The paper will provide a case study of how the various subsurface challenges typical to the Tampa region can be overcome in a practical manner through proper communication and planning while meeting the schedule and coordination demands of the project.