Three-dimensional advanced numerical approaches to the seismic soil and structural response analyses

A 3D non-linear finite element approach is developed to study the free-field seismic ground response and the soil-structure interaction (SSI) phenomena at the Lotung site (Taiwan) during the earthquake event occurred on May 20 1986. The site was extensively instrumented with down-hole and surface ac- celerometers, these latter located also on a 1/4–scale nuclear power plant containment structure. An advanced constitutive model is adopt- ed for simulating the soil behaviour, while a linear visco-elastic be- haviour is assumed for the structural model. The free-field and SSI analyses are carried out applying both the NS and EW horizontal components of the acceleration time history as recorded at the depth of 47 m b.g.l. The predicted ground response re- sults are in fair agreement with the recorded motion at depth and at the surface. The dynamic response of structure is well captured for this specific seismic event, thus confirming the validity of the numerical approach

Modellazione numerica del comportamento dinamico di gallerie superficiali in terreni argillosi

Lo studio del comportamento delle strutture in sotterraneo soggette ad azioni sismiche va affrontato in maniera diversa rispetto a quanto viene fatto comunemente per le strutture in elevazione. Mentre il comportamento di queste ultime è regolato dalle caratteristiche inerziali della struttura stessa, la risposta dinamica delle strutture in sotterraneo è governata dalla risposta deformativa del terreno circostante e dalla loro interazione. Questa differenza è una conseguenza della trascurabile inerzia della costruzione in sotterraneo rispetto a quella del terreno che la circonda. In relazione ai danni prodotti dalle vibrazioni del terreno al passaggio delle onde sismiche, gli stati deformativi che può subire una galleria in seguito ad esso possono essere sintetizzati secondo gli schemi riportati in Figura 1.1 (Owen e Scholl, 1981), dove si assimila la struttura in sotterraneo ad una trave elastica sottoposta alle deformazioni imposte dal terreno circostante. Con riferimento all’asse della galleria risulta quindi necessario analizzare il comportamento dell’opera secondo due direzioni: • direzione longitudinale: la galleria è sollecitata secondo la sua direzione longitudinale dalla deformazioni di compressione ed estensione che si sviluppano secondo il suo asse e dalle deformazioni flessionali che si originano dalle vibrazioni delle particelle di terreno in direzione perpendicolare al suo asse; • direzione trasversale:la galleria è sollecitata nel piano trasversale dall’azione di onde di taglio con direzione di propagazione pressoché perpendicolare al suo asse che portano all’ovalizzazione della sezione strutturale (Wang, 1993). Il comportamento di una galleria in presenza di sisma può essere analizzato sia ricorrendo a soluzioni in forma chiusa basate su approcci di tipo analitico sia effettuando delle analisi dinamiche complete mediante, ad esempio, un codice di calcolo non lineare agli Elementi Finiti (FEM). Nel primo caso gli effetti locali sono tenuti in conto attraverso specifiche analisi di propagazione locale, finalizzate alla definizione delle caratteristiche del sisma alla quota della galleria (approccio disaccoppiato). Le analisi FEM, invece, permettono di valutare il comportamento della galleria tenendo conto in maniera più realistica dell’interazione terreno-rivestimento, del comportamento non lineare del terreno e dell’accelerogramma di progetto nella sua interezza e non solo attraverso parametri sintetici (approccio accoppiato). Il problema della propagazione monodimensionale è stato analizzato adottando l’approccio lineare equivalente implementato nel codice EERA (Bardet et al., 2000). Le sollecitazioni nel rivestimento della galleria sono state calcolate, limitatamente alla sola direzione trasversale, facendo riferimento alle equazioni proposte da Wang (1993) sia per condizioni di full-slip sia per quelle di no-slip tenendo conto della differente rigidezza del terreno e della struttura. Le analisi FEM sono state condotte in condizioni di deformazione piana con il codice PLAXIS. Nell’ottica di un confronto con i risultati ottenuti dall’approccio disaccoppiato, in un primo gruppo di analisi è stato utilizzato per il terreno un modello costitutivo di tipo visco-elastico. In una seconda serie di analisi è stato introdotto come ulteriore ingrediente la plasticità, facendo riferimento al criterio di resistenza di Mohr-Coulomb. Tutte le analisi numeriche sono state condotte in condizioni non drenate e lo smorzamento viscoso è stato introdotto secondo la formulazione di Rayleigh

Analysis of Tunnel Behaviour Under Seismic Loads by Means of Simple and Advanced Numerical Approaches

In this paper different approaches aimed at investigating the dynamic behaviour of circular tunnels in the transverse direction are presented. The analysed cases refer to a shallow tunnel built in an ideal soft clayey deposit. The adopted approaches include one-dimensional (1D) numerical analyses performed modelling the soil as a single phase visco-elastic non-linear medium, the results of which are then used to evaluate the input data for selected analytical solutions proposed in the literature (uncoupled approach), and 2D fully coupled Finite Element simulations adopting visco-elastic and visco-elasto-plastic constitutive assumptions for the soil and the lining (coupled approach). The results are proposed in terms of increments of seismic-induced loads in the transverse direction of the tunnel lining. The different constitutive hypotheses adopted in the coupled numerical approach prove to play a significant role on the results. In particular, the plasticity-based analyses indicate that a seismic event can produce a substantial modification of the loads acting in the lining, leading to permanent increments of both hoop force and bending moment

Key features of the novel geothermal heat exchanger prototype installed at the Brenner Base Tunnel

The design, installation, and testing of an innovative geothermal heat exchanger, tailored for tunnels excavated by Tunnel Boring Machines, will be presented. The prototype was developed by the joint efforts of BBT SE, involved in the construction of a new railway base tunnel system connecting Italy and Austria, and the University of Bologna, engaged in applied research over various aspects of the BBT system. The geothermal heat exchanger consists in a modular horizontal closed-loop system located in the exploratory tunnel of the BBT system, specifically in the space dedicated to collect the drained water at the lining invert. Due to the type of the heat exchange process, working with the drainage water, and for its compact design and simple installation procedure, the prototype was called “Smart Flowing”. Modules were built outside and later moved inside the tunnel, and eventually placed and assembled concurrently to the advancement of the Tunnel Boring Machine. Specific tests were performed to prove the reliability and the efficiency of the system, by simulating the work of a heat pump conditioning system in both heating and cooling modes. Finally, a preliminary assessment of the economic and environmental potential of this innovative prototype was carried out. First results showed the performance of the system for both heat dissipation and extraction. The drainage water flow guarantees a continuous recovery to the natural state, thus improving efficiency compared to classic geothermal heat exchangers. Economic savings and reduction of pollutants and greenhouse gases, as compared to burning fossil fuels, can reach up to 70%

Exploitation of drainage water heat. A novel solution experimented at the Brenner Base Tunnel

Deep tunnels in permeable fractured rock-masses and under high piezometric levels can drain notable volumes of warm water, which are collected under gravity in specific conduits towards the portals, where heat can be exploited. The utilization of this energy source is generally narrowed by the limited presence of end-users near the portals, while other promising heating and cooling needs can be found directly along the tunnel length. The work presents the design, construction and installation of a geothermal system prototype exploiting the drainage water heat directly inside the tunnel. The prototype was named Smart Flowing due to the peculiarity of its heat exchange process. The system was realized and installed inside the exploratory tunnel of the Brenner Base Tunnel, near the border between Italy and Austria. The Smart Flowing modules were built outside and later moved inside the tunnel, where they were placed and assembled concurrently to the advancement of the Tunnel Boring Machine. A design procedure was proposed and validated against a testing and monitoring campaign. The data from the experimental activity confirmed that the drainage water flow guarantees long-term stabilization of circulating water temperature and fast heat recovery afterwards, thus securing the considerable power and performance values of a water-water heat pump connected to the system. A sensitivity analysis allowed the reproduction of different working scenarios, in order to generalize the application of Smart Flowing beyond the specific installation context

Consideration of the mechanical damage behavior of rock salt during calculation of infiltration-cracks in the edge zone of gas storage caverns

Underground storage in salt caverns is a preferred method for the intermediate storage of natural gas to cover seasonal fluctuation in consumption and commercial gas storage. The prove of the stability and tightness of the storage required for safe operation is continuously adapted to the current state of the art. For many years, an intensive scientific investigation has been carried out within the frame-work of repository research with continuous optimization of the rock mechanical modelling of the material behavior of rock salt. From the elaboration of the research results on the pressure-driven infiltration processes into the primarily non-permeable salt rock, it emerges that during gas storage operation, in addition to the areal infiltration, the formation of macroscopic infiltration-cracks in the cavern surrounding salt rock is to be expected as well. This thesis deals with the computational simulation of macroscopic infiltration-cracks within the scope of theoretical modelling of salt cavern behavior during gas storage, taking into account additional mechanical damage processes in the rock salt. On the basis of variational calculus, the infiltration fracture propagation will be evaluated, considering different model approaches in material behavior of the cavern surrounding rock salt mass. As a result of the present work, it should be noted that with regard to the propagation of infiltration-cracks in gas caverns, constitutive model approaches for the description of the mechanical damage and healing behavior of rock salt can be neglected for a conservative assessment

Earthquake Geotechnical Engineering Aspects of the 2012 Emilia-Romagna Earthquake (Italy)

On May 20, 2012 an earthquake of magnitude ML=5.9 struck the Emilia Romagna Region of Italy and a little portion of Lombardia Region. Successive earthquakes occurred on May 29, 2012 with ML=5.8 and ML=5.3. The earthquakes caused 27 deaths, of which 13 on industrial buildings. The damage was considerable. 12,000 buildings were severely damaged; big damages occurred also to monuments and cultural heritage of Italy, causing the collapse of 147 campaniles. The damage is estimated in about 5-6 billions of euro. To the damage caused to people and buildings, must be summed the indirect damage due to loss of industrial production and to the impossibility to operate for several months. The indirect damage could be bigger than the direct damage caused by the earthquake. The resilience of the damaged cities to the damage to the industrial buildings and the lifelines was good enough, because some industries built a smart campus to start again to operate in less of one month and structural and geotechnical guidelines were edited to start with the recovering the damage industrial buildings. In the paper a damage survey is presented and linked with the ground effects. Among these, soil amplification and liquefaction phenomena are analyzed, basing on the soil properties evaluation by field and laboratory tests. Particular emphasis is devoted to the damaged suffered by the industrial buildings and to the aspects of the remedial work linked with the shallow foundation inadequacy and to the liquefaction mitigation effects

PRENOLIN project. Results of the validation phase at sendai site

One of the objectives of the PRENOLIN project is the assessment of uncertainties associated with non-linear simulation of 1D site effects. An international benchmark is underway to test several numerical codes, including various non-linear soil constitutive models, to compute the non-linear seismic site response. The preliminary verification phase (i.e. comparison between numerical codes on simple, idealistic cases) is now followed by the validation phase, which compares predictions of such numerical estimations with actual strong motion data recorded from well-known sites. The benchmark presently involves 21 teams and 21 different non-linear computations. Extensive site characterization was performed at three sites of the Japanese KiK-net and PARI networks. This paper focuses on SENDAI site. The first results indicate that a careful analysis of the data for the lab measurement is required. The linear site response is overestimated while the non-linear effects are underestimated in the first iteration. According to these observations, a first set of recommendations for defining the non-linear soil parameters from lab measurements is proposed. PRENOLIN is part of two larger projects: SINAPS@, funded by the ANR (French National Research Agency) and SIGMA, funded by a consortium of nuclear operators (EDF, CEA, AREVA, ENL)