SDMT testing and its use in the numerical modelling of a deep excavation

The role of in situ tests in numerical analyses of deep excavations is investigated. The construction of a metro station in Barcelona required a deep excavation in a densely built urban area. Geological conditions were complex and challenging, involving soft alluvial materials below groundwater level. A comprehensive instrumentation system allowed monitoring the deep excavation-induced movements in the area and finite-element numerical analyses were carried out to reproduce the complex construction process. Results from two different numerical models are compared to field observations. The first model was based on data resulting from conventional analyses of site and laboratory investigations and initial monitoring results. The second model was instead created using only seismic dilatometer data, but using instead a systematic approach to calibrate soil stiffness nonlinearity. Comparison of numerical results and subsequent monitoring show that, although reasonable agreement is obtained for both modelling approaches, the SDMT-based one appears more accurate. Site characterization based on seismic dilatometer data may prove very useful in deep excavation analyses, particularly if the soils are difficult to sample.