Geotechnical Aspects in Seismic Soil-Structure Interaction of San Gimignano Towers: Probabilistic Approach

Abstract. This paper summarizes the main aspects of geotechnical modeling and soil-structure interaction analyses performed for the seismic risk assessment of the San Gimignano towers. Morphological, stratigraphic, and geotechnical characterization of the subsoil is described in the first part of the paper. The results of a geotechnical survey (including two borings with standard penetration tests, downhole tests, and laboratory tests on three undisturbed samples, both in static and dynamic conditions) are described and analyzed. Seismic ground response as well as soil-structure interaction analyses are presented in the second part of the paper. One-dimensional ground response analyses were performed by using a probabilistic approach, and the results were compared with those from ambient noise vibration measurements. The seismic input motions were selected from existing databases of actual strong motion recordings, according to seismic hazard of the site. Soil-structure interaction analyses were performed on a simplified model of the most important San Gimignano tower (Torre Grossa) by applying a numerical multistep method based on the principle of superimposition. The comparison of the obtained results with those presented in previous studies for fixed-base conditions shows small differences (approximately 2%) in the fundamental period of vibration of the tower estimated by means of the different approaches.