Case Study- Effects of Undisclosed Large Diameter Sinkhole on Construction, Clearwater, Florida
Karl A, Higgins, III, P.E., BC.GE
Sinkholes remain a significant geotechnical challenge in many parts of Florida, and even with modern best practices, dormant karst features can occasionally reactivate during construction. This presentation will highlight a complex case study from a multi-family apartment project in Clearwater, Florida, where a previously undiscovered large-diameter sinkhole was reactivated during grading and construction activities. The resulting settlement severely impacted a 18-foot-tall segmental retaining wall and nearby utilities, prompting a multi-year investigation and remediation effort between 2022 and 2024.
Extensive field data, including deep soil borings, vertical inclinometers, robotic total station measurements, and traditional settlement surveys were collected to evaluate the sinkhole’s behavior. Initial remediation included reconstructing the damaged retaining wall using lightweight glass-blown aggregate to reduce foundation stress, but continued movement revealed deeper instability. Subsequent monitoring and finite element modeling confirmed a large circular failure zone linked to the sinkhole.
The final remediation phase incorporated a robust structural solution using 110-foot-long sheet piles with deadman anchors, which successfully stabilized the wall and surrounding ground. Adjacent buildings affected by settlement were underpinned and jacked to restore elevations. The presentation will share lessons learned, emphasizing the importance of monitoring, modeling, and collaboration in addressing complex karst-related failures in urban construction environments.
Karl Higgins brings more than 35 years of experience in Geotechnical Engineering and Building Construction Inspection, serving clients across both the public and private sectors, including local, county, state, and federal agencies. A Board-Certified Geotechnical Engineer through the Academy of Geo-Professionals (ASCE), Karl has held numerous leadership positions throughout his career. Most recently, he served as Chief Engineer for a national engineering firm with over 850 employees, where he oversaw teams of engineers, geologists, and technicians throughout the DMV region.
Karl is an active member of professional organizations including ASCE, NAIOP, the Deep Foundations Institute, and the Pile Driving Contractors Association. He is also a licensed Professional Engineer in Maryland, Virginia, the District of Columbia, Delaware, Pennsylvania, New Jersey, Florida, and North Carolina.
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