Fernandina old Wall of Lisbon: Characterization towards its preservation

Abstract

The Fernandina old fortress of Lisbon started to be built in 1373. It is composed by 76 towers and 35 entrances along the fortress that is closed with an extension of 4.69 km, having two main sections: East, limited between St. George's Castle and Terreiro do Trigo Street, and West, starting also in the St. George's Castle and finished at Misericórdia Street. The construction technology of those sections is mainly rammed earth with an average height of 8 m. Some sections seem to be totally homogeneous but there are other composed of two parallel stone masonry walls with a nucleus filled with compacted earth. The thickness of the fortress wall is variable between 1.75 and 2.20 m. To build with rammed earth technique, humid excavated earth was placed in layers on a wood formwork and manually compacted reducing the thickness of each layer. A succession of compacted layers completed the formwork, which was laterally displaced to build the next rammed earth block. After completing the rammed earth level, the formwork was displaced to the upper level and the same cycle continues up to the top level of the wall fortress. Sometimes, particularly in defensive structures, air lime was added to stabilize the humid earth, obtaining the so called "military rammed earth". In the other case, the humid earthen materials were placed in layers and compacted inside the two parallel masonry walls that acted as formwork. The fortress is nowadays completely "emerged" and surrounded by the city. Several interventions mainly performed on old buildings confining with, or including, the old fortress have been held in the last years. Some of the sections present renders and repointing mortars that are not originals. Nevertheless, so far there is a lack of information on the materials, originals and applied in the history of interventions. Therefore, this study intends to present the characterization made in situ by visual observation and non-destructive techniques and in laboratory on samples that was possible to obtain from some sections of the old fortress walls. It is expected that the information from the material characterization will be useful to support decisions on future interventions, namely on the definition of repair mortars that need to be compatible and assure efficient conservation of sections that are being accessible of the old wall. ; authorsversion ; published