Numerical analysis of deep-anchored excavations in residual soil with reliquiae layers

The coastal region of Boa Viagem and Icaraí, located in the city of Niterói/RJ, has been the subject of several studies focusing on its geotechnical and geological characteristics, particularly due to the presence of a major fault extending into Guanabara Bay. Reliquiae weak layers are widespread in the local soil, with strength parameters significantly different from those of the surrounding residual soil, therefore commanding the stability conditions of excavations in the area. To support the construction of a new residential building complex near Boa Viagem Hill, several 30 to 40 m deep excavations are planned, with the stability ensured through anchored tieback walls and soil nailing systems. This paper aims to analyze the behavior of two key excavation sections considering the impact of the reliquiae soil layers. A 2D numerical analysis was conducted using Plaxis 2D, applying the Hardening Soil Small Strain constitutive model for all soil layers. Displacement profiles and the evolution of average anchorage loads were assessed. The results showed that the highest lateral displacements were concentrated along the reliquiae weak layers, particularly in the final three-quarters of the excavation, indicating a tendency of bottom heaving. At the same depth, the anchors experienced a 7% increase of the average axial loads by the final construction stage. The loads at the facing connections ranged from 60% to 80% of the maximum mobilized nail loads.