Methods of protecting archaeological sites against extreme climatic events

Archaeological sites manifest systematically a high vulnerability level when facing extreme climatic events, as for instance weather phenomena, like great return period rainfall. The reason often lies in the fact that shelters are initially designed as temporary to provide protection during the early phases of excavation, but they sometimes become permanent or last for a long time because of the protracting of the operations. Thus, they are not adequate for that long-term purpose and expose the findings to high risks. The present work aims at examining the main recurring issues and controversies involving heritage protection by means of shelters. Lightweight and long spanned shelters are often required to guarantee site preservation little interfering with the remains and the excavation works. Grid shells are fit for such purpose because of their structural ability to withstand heavy loads with respect to their own weight, and of their ability to fit in free form surfaces. This attitude represents an advantage due to the possibility to manage easily various constraints, such as plan complexity with only few supports available. The research of a grid shell system able to assure modularity, reversibility, sustainability, waterproofing and environmental control led to two generic adapting solutions: the Static Aware Voronoi grid shell and the Reciprocal Frame grid shell. Moving from a continuous surface, a digital workflow is defined in order to achieve effective long-term protection with a short-time planning phase. Two case studies are examined: a modular Voronoi free form vault and the free form reciprocal framed shelter for the Roman Shipwrecks of Pisa.