Geotechnical investigation of Ivens Shaft in Lisbon

Construction of underground structures in urban areas requires a detailed assessment of the associated movements imposed on adjacent structures and services and in particular of any damage that may be caused. The most efficient way of investigating these issues is through the application of advanced numerical analysis, using for instance the finite element method. However, for a useful analysis to be performed, a high quality ground investigation must be conducted in order to derive the necessary soil parameters for numerical modelling. This thesis focuses particularly on the case study of the Ivens shaft located near to the Baixa-Chiado station of the Lisbon Metro, Portugal. This is an underground structure of a complex shape and significant depth, situated in the centre of the city and it is therefore important to assess the influence of its construction on the existing adjacent structures and services. In the first part of the thesis the results of the geotechnical survey performed on the relevant Miocene formations located at the Ivens shaft site are presented and discussed. In particular, the “Areolas de Estefânia” formation was characterised in detail since this layer had not sustained significant investigation in the past, mainly due to difficulties in sampling. From the extensive characterisation undertaken, which included both field and advanced laboratory tests, it was possible to derive a suitable framework for the different formations in terms of strength and stiffness. Such information was then used to calibrate appropriate soil constitutive models for use in the numerical analyses. In this respect, the new generation of algorithms, known as Genetic Algorithms, was employed to increase the efficiency and accuracy of the calibration procedure. The second part of the thesis focuses on the 3D numerical modelling of the excavation of the Ivens shaft, which was performed employing the state-of-the-art software ICFEP (Imperial College Finite Element Program). The results obtained permitted the quantification of the shaft and ground movements and their effect on adjacent structures. Particular attention was given to the influence of the excavation on the Baixa-Chiado station and on the adjacent buildings founded near the ground surface. Finally, a parametric study was carried out in order to investigate a number of shaft parameters that may affect the movements and to provide more general guidance for shaft construction