Contribution of Paleosol Stratigraphy to Geotechnical Modeling: A Case Study of the Two Towers in Bologna

Paleosol identification is a valuable tool for stratigraphic correlation in fine-grained alluvial successions, applicable at both local and regional scales. This study investigated paleosol formation and their key physical properties, focusing on pedogenic processes affecting soil mechanical behavior. A methodology was developed for identifying paleosol horizons using common in situ tests, particularly cone penetration tests (CPTs), facilitating the transition from a paleosol-based stratigraphic model to a geotechnical–stratigraphic model, for engineering applications. This approach was applied to data from the historic center of Bologna, Italy, including the Asinelli and Garisenda Towers, two medieval structures founded on fine-grained alluvial deposits. Radiocarbon-dated paleosols from the Late Pleistocene in this area show increased strength and stiffness, as revealed by in situ testing, likely attributed to cementation and aging. Comparing borehole data with CPTs enabled the identification of weakly developed paleosols (Inceptisols), enhancing geotechnical model accuracy. The paleosol-based stratigraphic model presented in this study provides critical information for developing a refined geotechnical model that can account for even subtle variations in microstructure, features often overlooked by conventional CPT-based and core-based soil profiling methods, and highlights significant subsurface settlements experienced by the Two Towers over time. This research demonstrates the effectiveness of the proposed interdisciplinary approach, emphasizing the potential of paleosol identification for engineering applications in complex subsurface environments.