Secondary Compression of Deep Foundations in Carbonate Soils: An InSAR Study of Sunny Isles, Florida

Abstract

Six-year interferometric synthetic aperture radar (InSAR) measurements of over 20 high-rise buildings in Sunny Isles, Florida, reveal persistent postconstruction settlements up to 5 cm. Supported by auger cast-in-place (ACIP) piles in a heterogeneous carbonate profile, these building-specific deformations cannot be attributed to regional subsidence or primary consolidation of the predominantly free-draining granular strata. Log-time and power-law models both reproduce the 6-year observations well and produce comparable 100-year extrapolations, with the power-law model yielding slightly more conservative estimates at long time horizons. Because both models fit the observational data equally well, the 100-year estimates are interpreted as scenario-based serviceability extrapolations rather than deterministic predictions. The inferred field-scale secondary compression indices exceed typical laboratory values for sands at the majority of sites, indicating that intrinsic granular creep alone cannot explain the observed deformations. Instead, the observations reflect a complex, system-level foundation–soil response involving carbonate stratigraphy, pile-group interaction, and progressive stress redistribution, the relative contributions of which cannot be quantified from the surface observations alone. To assist practitioners, the creep ratio R = A / s i is introduced, where A is the log-time settlement slope fitted to InSAR data and s i is the construction-stage settlement estimate. Used retrospectively, R quantifies whether past designs were conservative with respect to long-term creep; used prospectively, it provides a screening tool for new designs drawing on InSAR records from neighboring buildings. As InSAR monitoring becomes more widely available, this framework offers a path toward integrating satellite-based settlement observations into routine serviceability assessments for high-rise structures in coastal carbonate environments.