COMPARATIVE TECHNICAL, ECONOMIC, AND SAFETY ANALYSIS OF TOP-DOWN AND BOTTOM-UP METHODS IN URBAN TRENCH EXCAVATIONS

• DOI: https://doi.org/10.22533/at.ed.1317652604051

• Palavras-chave: Top-Down construction; underground subway stations; diaphragm walls; urban excavations; risk analysis.

• Keywords: Top-Down construction; underground subway stations; diaphragm walls; urban excavations; risk analysis.

• Abstract:

  This paper presents a comparative technical, economic, and safety analysis between the Top-Down and Bottom-Up construction methods applied to the construction of underground subway stations in urban environments. The study is based on a representative hypothetical case located in the West Zone of the city of São Paulo, considering the geological and geotechnical conditions of the Resende Formation as determining factors in the selection of the construction method. The execution processes of each methodology, the risks associated with the excavation and shoring stages, and the technical criteria for selecting construction systems were evaluated. The direct cost analysis was based on SINAPI prices (March 2026, State of São Paulo) for conventional materials, and on estimates adjusted by the INCC-DI index for specialized services. The results indicate that the Top-Down method showed a reduction of approximately 18% in construction time and 4.6% in total direct cost compared to the Bottom-Up method. Regarding safety, the two methods presented equivalent overall scores (78 and 77, respectively), differing mainly in the nature of the risks: the Bottom-Up method concentrates moderate risks distributed throughout the entire project, while the Top-Down method introduces high-criticality risks in specific phases of confined excavation, requiring more rigorous control measures. The Top-Down method proved to be more suitable for the analyzed context, being especially recommended in densely populated urban areas where the reduction of surface disturbances and the control of deformations are critical factors.