Subsoil characterization and stability analysis for the Bourbon del Monte Palace in Piancastagnaio (Siena, Italy)

The historical Bourbon del Monte Palace in Piancastagnaio (Siena, Italy) dates to the 17th century and represents an uncommon example of feudal architecture in Tuscany. It was inhabited until the end of the ’80s of the last century when, due to the high degree of instability achieved, it was declared unfit for use by the Public Authorities. The Palace lays on a sloping site, on the edge of fractured trachyte blocks mixed with alluvial deposits. It is characterized by four floors above ground and a basement at the South-East corner, while the North façade has two floors. Severe degradation phenomena of the building consist of multiple cracks diffused along the external and the inner masonry; furthermore, significant water infiltration from the floor has been observed in the South-East basement since the ’80s. Previous investigations have shown that the Palace has undergone two distinct settlements systems: one dates before the ’70s and may have caused the cracks along the South wall of the building; the other, more recent and probably related to the water infiltration on the basement, may have caused the damage to the South-East wall. This paper investigates the source of this second settlements system by modeling and analyzing a 2D soil section close to the South-East corner of the building. Firstly, the collected geotechnical and geological data and the modeling of the analyzed section are presented. Afterwards, the results of the numerical simulations are shown and discussed, analyzing the effects of the estimated settlements on the observed structural damage.