Finite locally resonant Metafoundations for the seismic protection of fuel storage tanks

This paper introduces a novel seismic isolation system based on metamaterial concepts for the reduction of ground motion-induced vibrations in fuel storage tanks. In recent years, the advance of seismic metamaterials has led to various new concepts for the attenuation of seismic waves. Of particular interest for the present work is the concept of locally resonant materials, which are able to attenuate seismic waves at wavelengths much greater than the dimensions of their unit cells. Based on this concept, we propose a finite locally resonant Metafoundation, the so-called Metafoundation, which is able to shield fuel storage tanks from earthquakes. To crystallize the ideas, the Metafoundation is designed according to the Italian standards with conservatism and optimized under the consideration of its interaction with both superstructure and ground. To accomplish this, we developed two optimization procedures that are able to compute the response of the coupled foundation-tank system subjected to site-specific ground motion spectra. They are carried out in the frequency domain, and both the optimal damping and the frequency parameters of the Metafoundation-embedded resonators are evaluated. As case studies for the superstructure, we consider one slender and one broad tank characterized by different geometries and eigenproperties. Furthermore, the expected site-specific ground motion is taken into account with filtered Gaussian white noise processes modeled with a modified Kanai-Tajimi filter. Both the effectiveness of the optimization procedures and the resulting systems are evaluated through time history analyses with two sets of natural accelerograms corresponding to operating basis and safe shutdown earthquakes, respectively.     

Analyses of the Distribution and Nature of the Natural Cementation of Quaternary Sediments: The Case of the Turin Subsoil (Italy)

The finding of a remarkable number of stratigraphies from mechanical surveys and water research wells, drilled in the urban area of Turin over the last few decades, has made it possible to reconstruct the geology of the subsoil in great detail. In particular, it has been possible to define the distribution of the cementation in the Quaternary alluvial sediments through geological planimetries that refer to different depths from the ground level. The cementation map of the Turin subsoil can be considered very useful for the planning of future underground works and for the definition of the necessary construction methods. An accurate mineralogical analysis has identified a “meniscus” type structure of the cementation; this leads us to believe that the cementation has formed in a vadose environment. The reason for the precipitation of the calcium carbonates is therefore probably due to infiltration of the slightly acidic meteoric water into the subsoil and not to the mixing of water with different temperatures, hardness and pH values, as some authors believed in the past.     

Stabilisation of the Excavation Face in Shallow Tunnels Using Fibreglass Dowels

Stability of the excavation face in shallow tunnels excavated in poor rock is at present a relevant problem in tunnelling. Even though face reinforcement with fibreglass dowels has proved to be efficient, there is still no reliable routine design method available. A new calculation procedure is illustrated in this paper for the analysis of face reinforcement with fibreglass dowels in shallow tunnels. The procedure is based on the limit equilibrium method applied to the rock core ahead of the face, and it offers a detailed evaluation of the interaction between each reinforcement element and the surrounding rock. The main calculation result concerns the safety factor of the excavation face with dowel reinforcement. On the basis of this safety factor, it is possible to identify the appropriate dowel lengths and the number of dowels. The procedure has been applied to two real cases, and satisfactory results have been obtained.     

A Combined Analytical and Numerical Approach for the Evaluation of Radial Loads on the Lining of Vertical Shafts

The evaluation of the load acting on a shaft support is of fundamental importance for the correct dimensioning of the structure. The load acting on the support can appear somewhat complex. One approach to define the load on the lining may be to use the convergence-confinement method (CCM) normally used in the tunneling design. This process involves intersecting the convergence-confinement (CC) curve with the support reaction line. However, in order to be able to adopt this technique, it is necessary to know the radial displacement of the shaft wall at the point in which the support is to be installed. Using the equations of Vlachopoulos and Diederichs (Rock Mech Rock Eng 42:131–146, 2009) the reaction line of the support can be calculated. Numerical models developed with Flac 2D v.6.0 considering the Mohr–Coulomb criterion and an ideal elasto-plastic behavior simulating stepwise excavation and support installation were developed. The relation between applied internal stress and radial displacement of the wall shaft, obtained by the numerical simulation was compared with the CC curve obtained by the CCM and it showed a good match between the two methods. However, an iterative procedure has also been used to insert the reaction line in the CC graph. The result shows lower initial displacements (and therefore greater radial stress) when compared with the values obtained by numerical calculation with the axisymmetric model. It is therefore recommended the combined use of the CCM (analytical method) and the axisymmetric numerical model (step by step simulation) to obtain the values of the final load on the lining and the final plastic radius, necessary for the correct design of supporting structures on the shaft wall.     

3D GIS Supporting Underground Urbanisation in the City of Turin (Italy)

This paper introduces a 3D geological and geotechnical model of the subsoil of the city of Turin managed by means of a Geographical Information System (GIS). The 3D GIS of the subsoil of Turin represents a useful decision-support tool in the underground management for engineering purposes and it’s here proposed as base geological elaborate to support future underground work in the city. In the final part of the paper, an application of the information coming from the 3D model is shown to define the characteristics of the optimal excavation machines (the type and disposition of tools on the head and the necessary engine power) for the future developments of the Underground Metro System.     

The Dimensioning of Dowels for the Stabilization of Potentially Unstable Rock Blocks on the Walls of Underground Chambers

The analysis of dowels (non pre-stressed passive reinforcements) for the stabilization of potentially unstable rock blocks due to sliding is one of the most interesting problems concerning the static of underground rock chambers. The stabilizing force produced by dowels is not in fact known a priori and it depends on the dowel–rock interaction. The parameters that influence the problem are not only the geometrical ones of the dowel, but also the mechanical characteristics of the rock and the orientation of the displacement vector of the block. A detailed study of the dowel–rock interaction has been carried out in this work. This analysis is able to lead to the evaluation of the axial and shear forces in the dowel in correspondence to the crossed discontinuity of the block. The vectorial composition of these two forces constitutes the stabilization force of the dowel. An extensive parametric analysis then made it possible to determine the great variability of the stabilization force of the dowel in function of the influential parameters of the problem. The graphics that were obtained can be considered a useful design instrument as they quickly allow the dimensioning of the dowels to be done to reach the required safety factor for the rock block.     

Mineralogical and isotopic properties of inorganic nanocrystalline magnetites

Inorganic magnetite nanocrystals were synthesized in an aqueous medium at 25°C, atmospheric pressure, ionic strength of 0.1 M, oxygen fugacity close to 0, and under controlled chemical affinity, which was maintained constant during an experiment and varied between different experiments. The total concentration of iron in the initial solutions, with Fe(III)/Fe(II) ratios of 2, was varied in order to measure the role of this parameter on the reaction rate, particle morphology, and oxygen isotopic composition. The reaction rates were followed by a pHstat apparatus. The nature and morphology of particles were studied by transmission electron microscopy and electron energy loss spectroscopy. Fractionation factors of oxygen isotopes were determined by mass spectrometry after oxygen extraction from the solid on BrF₅ lines. At low total iron concentrations, goethite and poorly crystalline iron oxides were observed coexisting with magnetite. At higher concentrations, euhedral single crystals of pure magnetite with an average characteristic size of 10 nm were formed, based on a first-order rate law with respect to total iron concentration. These results confirm that, under high supersaturation conditions, low-temperature inorganic processes can lead to the formation of well-crystallized nanometric magnetite crystals with narrow size distribution. The observed oxygen isotope fractionation factor between magnetite crystals and water was of 0-1‰, similar to the fractionation factor associated with bacterially produced magnetite. We suggest that the solution chemistry used in this study for inorganic precipitation is relevant to better understanding of magnetite precipitation in bacterial magnetosomes, which might thus be characterized by high saturation states and pH.     

Tests and model calibration of high‐strength steel tubular beam‐to‐column and column‐base composite joints for moment‐resisting structures

Performance‐based engineering (PBE) methodologies allow for the design of more reliable earthquake‐resistant structures. Nonetheless, to implement PBE techniques, accurate finite element models of critical components are needed. With these objectives in mind, initially, we describe an experimental study on the seismic behaviour of both beam‐to‐column (BTC) and column‐base (CB) joints made of high‐strength steel S590 circular columns filled with concrete. These joints belonged to moment‐resisting frames (MRFs) that constituted the lateral‐force‐resisting system of an office building. BTC joints were conceived as rigid and of partial strength, whereas CB joints were designed as rigid and of full strength. Tests on a BTC joint composed of an S275 steel composite beam and high‐strength steel concrete‐filled tubes were carried out. Moreover, two seismic CB joints were tested with stiffeners welded to the base plate and anchor bolts embedded in the concrete foundation as well as where part of a column was embedded in the foundation with no stiffeners. A test programme was carried out with the aim of characterising these joints under monotonic, cyclic and random loads. Experimental results are presented by means of both force–interstory drift ratio and moment–rotation relationships. The outcomes demonstrated the adequacy of these joints to be used for MRFs of medium ductility class located in zones of moderate seismic hazard. Then, a numerical calibration of the whole joint subassemblies was successfully accomplished. Finally, non‐linear time‐history analyses performed on 2D MRFs provided useful information on the seismic behaviour of relevant MRFs. Copyright © 2015 John Wiley & Sons, Ltd.