Seismic analysis of Underground works and practice: The case of MetroLima

The evaluation of the seismic behavior of underground structures represents one of the most actual seismic geotechnical and structural engineering research topics. In the last decades, different types of simplified and numerical approaches have been developed for the correct analysis of the seismic vulnerability of these important infrastructures and a series of laboratory tests for the seismic behavior characterization of the soils (e.g. resonant column test, etc.) and of the coupled soil-structure system (e.g. centrifuge test, etc.) have been conducted, especially after the recent strong earthquakes where the underground structures have been subjected to significant damages. In the same way, in the last few years, the Technical Codes are beginning to pay attention to the seismic design of these structures. Despite the significant development of knowledge, described above, still remain open several uncertainties of the correct reproduction of the underground structures behavior under seismic load. The goal of this research project is to further improve the knowledge of the underground structures behavior under seismic load, with the application of different simplified approaches, numerical models and laboratory tests, taking as case study the new Lima Metro line 2. In the first chapter, a short description of the underground structures behavior under seismic action is presented. Particular attention is devoted to the description of the underground structure seismic response during the most important recent earthquake events. Following the introduction, the second chapter reports a detailed description of the actual techniques for the evaluation of the seismic response of the underground structures, taking into special consideration the evolution of the numerical approaches of the coupled soil-structure interaction system and the definition of the non-linear behavior of the soil. In the third chapter, the attention is focused on the comparison between numerical methods and simplified approaches through the execution of sensitivity analysis considering the variation of the soil mechanical properties (in particular of the shear modulus) remaining within the category type B according to the limit, in terms of shear waves velocity, defined by Eurocode 8. The results, obtained by the application of the different type of approaches, are discussed from a critical point of view. The fourth chapter reports a detailed description of the case study: the project of the new Lima Metro line 2. Otherwise the structural characteristics of the metro stations, particular attention is devoted to the hydrogeological, geological and geotechnical characterization of the project area. A series of laboratory and in situ tests have been carried out in order to obtain the mechanical properties of the soils. In particular, the attention is focused on the Mercado Santa Anita metro station that is the first metro station built. For the evaluation of the seismic behavior of this station simplified decoupled approaches and numerical analysis are performed. In the fifth chapter, the final considerations of the results obtained by the execution of the different types of analysis are discussed, also considering as observed by the case study described in the fourth chapter.

La valutazione del comportamento sismico delle strutture interrate rappresenta uno dei più attuali argomenti di ricerca riguardanti l'ingegneria strutturale e geotecnica. Durante gli ultimi decenni, sono stati sviluppati differenti metodi di analisi semplificati e complessi in modo da poter cogliere il corretto comportamento sismico delle strutture interrate, supportati da un insieme di nuove prove di laboratorio utili alla caratterizzazione dinamica dei suoli.Negli ultimi anni anche le Normative internazionali hanno posto maggiore attenzione sulle prescrizioni riguardanti la progettazione in zona sismica di questo tipo di strutture. Nonostante questo importante sviluppo, però, rimangono ancora diverse incertezze sul comportamento sismico delle strutture interrate. L'obiettivo finale di questa tesi è quello di migliorare il grado di conoscenza del loro comportamento sismico attraverso prendendo come caso studio la nuova linea metropolitana di Lima realizzata da Salini - Impregilo, finanziatore di tale progetto di ricerca.