Mitigation of ground and retaining structure displacements due to excavations: analysis and modelling of soil structure interaction

The research is developed in the field of soil-structure interaction studies, focusing particularly on the retaining structures for deep excavations and on harbour berthing structures. As regard the first topic, the constant increase in the population of large cities leads to an ever-growing demand for infrastructures, which is often only possible through underground constructions. The execution of an excavation inevitably involves a change in the stress state of the ground and consequently it induces displacements and deformations. In urban environment and, particularly, in presence of a cultural and artistic urban heritage such as that of Italy, it is of crucial importance to minimize such induced displacements. This problem has led over the years, on the one hand, to the development of calculation procedures capable of providing reliable predictions of the effects induced by the execution of deep excavations and, on the other, has encouraged the investigation of construction solutions capable of reducing such displacements. The objective of the study, developed through numerical analyses, was to deepen the knowledge on the deformation response of different types of retaining structures, with the aim of providing design guidance in terms of the reliability and applicability of some “unconventional” retaining structures (buttress walls), also to meet current demands in the engineering field. From the results produced by the accurate 3D numerical analyses, indications of the magnitude of the displacements and the extent of the displacement zone in the vicinity of the excavation, associated with different geometric configurations of the retaining structure, were obtained, with the aim of providing practical feedback for design purposes, for the validation of results obtained by less thorough and accurate studies, under similar conditions, In addition , the results of the 3D numerical analyses, provide useful insights and indications within a preliminary design phase. A second topic taken into consideration in the present research work, still related to the topic of excavations and the impact on the ground and retaining works, took its cue from the problem of exponential growth in the size of commercial and cruise ships and, consequently, the need to make an existing infrastructure within an operating port adequate to ensure the berthing of modern ships. Solutions must be found for upgrading existing structures to actual requirements. As far as berthing retaining structures are concerned, a typical scheme of an “old” quay wall was considered, with the purpose of studying the problem of excavation at the foot with the aim of obtaining both displacement envelopes, similar to those available in the framework of deep excavation, and indications on the general safety of the structure. The performed numerical analyses, carried out with typical geometric and geotechnical have led to displacement envelopes and stability indicator values as a function of the excavation evolution, also to develop effective reinforcement and stabilization criteria. They can be useful in preliminary design phase of interventions because they provide indications on the amount of the ground settlement behind the quay and the extent of the area affected by them, depending on the excavation depth and the geometry of the ground improvement. For both the engineering problems that have been analyzed, related to the behavior of structures interacting with excavations, indications and quantitative guidelines (through design abacuses and the study of deformation mechanisms) were provided, useful for the preliminary design of interventions and for the eventual verification of results that can be assessed with simplified numerical analyses and analytical evaluations.