Effect of deep excavations and deformable retaining structures on neighboring buildings: A case study

In this paper, the case of a three-levels underground parking garage, needing deep excavations close to an existing masonry building, and of its deformable retaining structures is discussed. Although the geological survey showed a critical situation, no attention was paid to the provisional phases. Even when cracks appeared on the building shortly after the beginning of the excavations, and a monitoring system showed that damage on the building was increasing, no attention has been paid to the deformation of the slope behind the retaining structures. The sliding of the excavation front was avoided due to the prompt intervention of the courts and to provisional buttresses built in short time to sustain the excavation front. As a result, the nearby building had to be evacuated and could be reopened only after retrofitting works to the building and to the retaining structures. A theoretical analysis provides a deep understanding inside the phenomena that took place: excavations activated plastic deformations in the slope and in the retaining structures that reduced the safety factor of both the slope and the foundation system of the building below the admissible values. This could be foreseen provided a non-linear geotechnical analysis of the excavations-building interaction had been performed for the provisional phases.