The intervention was promoted by the Municipality of Alvito and consisted of a design-build project for the consolidation and safety measures aimed at the stabilization and rehabilitation of the Rossio Caves in Alvito, near the Hermitage of São Sebastião.

Intervention goal

The intervention was motivated by the need for geotechnical stabilization and the restoration of safety due to the high risk of permanent loss of the Rossio Cave/Quarry space and its impact on the surrounding area, which would jeopardize the preservation of the Hermitage of São Sebastião.

The galleries were excavated in the rock supporting the foundations of the hermitage and are documented as former limestone mining tunnels dating back to the 13th century.

The goal of providing safe conditions inside the Cave/Quarry also relates to enabling the space to be musealized and to showcase its historical character—the execution of millstones for the mills—and to integrate it into the tourist, museum, and cultural complex of the Alvito region.

Intervention stages and techniques

Solutions executed from outside the cave:

1. Implementation of an Instrumentation and Monitoring Plan, realized by installing topographic targets for periodic control readings, both at the Hermitage of São Sebastião and in nearby buildings showing cracks;
2. Diversion of the drainage system from the Hermitage of Saint Sebastian to prevent rainwater from flowing towards the cave’s influence zone;
3. Removal of a group of trees at Rossio whose roots were causing fracturing and disintegration of the rock mass;
4. Construction, from the outside, of a system of portal beams supported on micro-piles with a set of anchors/ties, with coring and injection to support the main vault of the cave and fill cracks;

Solutions executed from inside the cave:

1. Execution of Instrumentation and Observation Plan in the Cave vault, materialized by the placement of a set of topographic targets for periodic control readings;
2. Concrete encasement and grouting of the pillars through holes drilled by coring from the surface;
3. Assembly of temporary support structures for the vault during the execution of exterior anchors;
4. Application of reinforced shotcrete with welded mesh to consolidate the vault;
5. Installation of small-diameter anchors in areas facing the Hermitage and nearby buildings that presented cracks, to consolidate the rock mass in the area;
6. Installation of geodrains in the vault and cave walls to avoid restricting hydrological flow. Coring was used for drilling.

Applied Technique

A reinforcement system by anchors was implemented in the rock mass, and in the vault of the larger span cave, a prestressed reinforced concrete portal beam suspension system was constructed externally, supported by micro-piles.

Results

The structural safety of the Rossio Cave/Quarry space and the surrounding area, including the Hermitage of Saint Sebastian, was restored. This created the conditions for preservation, cultural enhancement, and the conservation of the memory of the entire site for the benefit of the population.