New Developments in the Control and Prediction of the Movements Induced by Deep Excavations in Soft Soils

The paper corresponds to the Pacheco Silva Lecture delivered by the author in September 2014. In the first part of the text, a general perspective of the movements induced by deep excavations in soft soils is outlined. The general report presented by Ralph B. Peck to the 1969 ISSMFE Mexico conference is taken as reference and the progress achieved since then in the control of the movements is emphasized. It is pointed out that such progress permits that in very demanding urban scenarios involving soft soils one should work towards a performance, with regard to induced movements, similar to (or even better than) that is achieved in comparable excavations in stiff soils. Starting from this general framework, some issues relevant to an effective control and to a reliable prediction of the movements are treated: the pre-stress of the strut system, the methodologies for providing support to the retaining wall before the removal of the soil, the surface settlements induced by the consolidation of the soil in the long-term and the influence of the non-linear behaviour of the reinforced concrete wall. Results of research on these topics are presented and discussed and general conclusions are extracted.