Giovanni Lanzano

Centrifuge Modeling of Seismic Loading on Tunnels in Sand

The purpose of the work is to provide an experimental benchmark on the seismic behavior of tunnels, with the final aim of calibrating numerical and analytical design methods. A series of plane-strain centrifuge tests with dynamic loading on a model tunnel was, therefore, carried out at the Schofield Centre of the Cambridge University Engineering Department (CUED). Four samples of dry uniform fine sand were prepared at two different densities, in which an aluminum-alloy tube was installed at two different depths. The tube was instrumented with strain gauges to measure hoop forces and bending moments at significant locations. To monitor the amplification of ground motion from the base to the surface, vertical arrays of accelerometers were placed in the soil model and along the box. The instrumentation also included linear variable differential transformers (LVDTs) that measured the soil surface settlement during all test phases. The test procedure and the results are described in this paper, showing the evolution of both accelerations and internal forces along the tunnel lining during the model earthquakes.

Seismic vulnerability of natural gas pipelines

Abstract This work deals with the analysis of the interaction of earthquakes with pipelines transporting and distributing natural gas for industrial and civil use. To this aim, a new large data-set of seismic information classified on the basis of selected seismological, geotechnical and structural parameters is presented and analyzed. Particular attention is devoted to continuous pipelines under strong ground shaking, which is the geotechnical effect due to passage of waves in soil. Results are provided in terms of the likelihood of the loss of containment with respect to Peak Ground Velocity (PGV), a seismic intensity parameter which may be easily retrieved either from local authorities and public databases or from site dependent hazard analysis. Fragility functions and seismic intensity threshold values for the failure and for the loss of containment of gas from pipeline systems are also given. The obtained functions can be easily implemented in existing codes and guidelines for industrial risk assessment, land-use planning, and for the design of public distribution network, with specific reference to Natural—Technological interaction (Na-Tech).

Experimental and numerical study on circular tunnels under seismic loading

This paper compares the experimental results of a set of centrifuge models of tunnels in sand under seismic loadings with the predictions of finite element dynamic analyses and of simplified methods. In order to characterise the soil behaviour, mobilised shear stiffness and damping ratio of the sand model have been back-calculated from the experimental results according to two different procedures. Starting from the accelerometer measurements, one was based on the transfer functions from surface to base and the other one on the average shear stress–strain cycles along the sand layer. A series of viscoelastic 2D dynamic analyses were performed to simulate the model tests by a linear equivalent approach. The equivalent shear stiffness and damping ratio determined from stress–strain cycles were used as input values for the analyses. The shear stress transfer at the ground-lining interface was back-analysed to calibrate the interface elements used in the numerical code, in order to improve the assessment of the transient changes of hoop force. Finally, the numerical results have been compared to analytical solutions, widely adopted in the design, and to the experimental data in terms of transient increments of internal forces in the lining. Such a comparison indicates that the analytical formulations give a good estimation of the seismic increment of bending moment in the lining and a reasonable lower bound for the transient changes of hoop forces, provided that cyclic shear strains are correctly evaluated.

Site characterization of Italian accelerometric stations

The last release of the strong-motion database ITACA (ITalian ACelerometric Archive v 2.1, http://itaca.mi.ingv.it) includes, to date, about 25,222 three-component accelerometric waveforms generated by 1365 earthquakes with magnitude between 3.0 and 6.9 and recorded by 1210 stations in the time frame 1972–2015. One of the main goals of ITACA is to improve the characterization of the recording sites from the geological and geophysical point of view and to provide seismic classification according to Italian seismic code. To this aim, metadata of recording stations are stored in three main thematic levels (topographic features, geological features and geophysical measurements) useful for a large variety of applications in engineering seismology or earthquake engineering. In particular, 206 recording stations have been characterized by quantitative measurements of velocity profiles, conducted through different techniques (active and/or passive), and the VS,30 values are available in ITACA 2.1. Moreover, 357 horizontal to vertical spectral ratios of Fourier spectra of ambient noise and the value of the fundamental frequency are also accessible. All details about the stations contained in the ITACA database are described in specific reports.

Update of the single-station sigma analysis for the Italian strong-motion stations

This paper is a reappraisal of the study on the single-station sigma for Italian strong-motion stations carried out by Luzi et al. (Bull Seismol Soc Am 104:467–483, 2014). A residual analysis considering the time interval 1972–2015 is carried out on two datasets, using 4.0 and 3.5 as magnitude thresholds, and the ground motion prediction equations by Bindi et al. (Bull Earthq Eng 9:1899–1920, 2011) as reference model for the calculations of the expected median intensity measures. The magnitude threshold of 3.5 is selected with the aim of obtain the largest number of records for each station and evaluate the influence of low magnitude events on the standard deviation of the residual components. The dataset contains about 8400 waveforms, relative to 522 events, recorded by 600 strong-motion stations, about five times the stations considered in Luzi et al. (2014). We also discuss elements that can influence the variability at individual station, as the number of records, the presence of analog waveforms and records from multiple source-to-site paths. For each station, the event-corrected single-station standard deviation for an individual site, ϕss,s, and the site-term, δS2Ss, have been provided. The results of this study can be used as input for the site-specific probabilistic seismic hazard assessment in Italy, removing the ergodic assumption.

NESS1: A Worldwide Collection of Strong‐Motion Data to Investigate Near‐Source Effects

The availability of high-quality waveforms recorded in epicentral areas of moderate-to-strong earthquakes is a key factor for investigating ground-motion characteristics close to the seismic source. In this study, near-source strong-motion waveforms (named NESS1) were collected from worldwide public archives with the aim of building a flat file of high-quality metadata and intensity measures (IMs) of engineering interest. Particular attention was paid to the retrieval of reliable information about event sources, such as geometries and rupture mechanisms that are necessary to model near-source effects for engineering seismology and earthquake engineering applications. The accelerometric records are manually and uniformly processed, and the associated information is fully traceable. NESS1 consists of about 800 three-component waveforms relative to 700 accelerometric stations, caused by 74 events with moment magnitude larger than 5.5 and hypocentral depth shallower than 40 km, with Joyner–Boore distance up to 140 km. Ground-motion data were selected to have a maximum sourceto-site distance within one fault length, defined through seismological scaling relations. About 40 records exhibit peak acceleration or peak velocity exceeding 1g or 120 cm=s, and they represent some of the largest ground motion ever recorded. Evidence of near-source effects was recognized in the NESS1 dataset, such as velocity pulses, large vertical ground motions, directional and hanging-wall amplifications and fling step. In particular, around 30% of the records was found to exhibit pulse-like characteristics that are possibly due to forward rupture directivity. Electronic Supplement: Table listing the main features of the selected events, including the references of fault geometry parameters and Figures showing further metadata and intensity measures distributions of the NESS1 flat file.

Experimental Assessment of the Stress–Strain Behaviour of Leighton Buzzard Sand for the Calibration of a Constitutive Model

Abstract A number of constitutive models are nowadays implemented in numerical codes which simulate the stress–strain behaviour of soil from very small to large strain. In this paper, the mechanical behaviour of Leighton Buzzard sand (grade E), used worldwide for physical modelling, has been thoroughly characterized by laboratory testing along several stress paths. Tests were aimed at calibrating a constitutive model, that allows considering stiffness nonlinearities in a wide range of strains, in the framework of isotropically hardening plasticity. As a validation, the results of dynamic centrifuge tests on a layer of the same sand were compared with finite element predictions.

Engineering geology model for seismic vulnerability assessment of critical infrastructures

Abstract The development of reliable subsoil models is one of the key points for the assessment of the seismic performance of existing strategic infrastructures, especially in many European countries where the seismic hazard varies from moderate to high. The strategic infrastructures are structures and components which have a crucial role in the social and economic development of a modern country, and include lifelines and industrial plants. Lifelines frequently have a linear development and can be affected by very heterogeneous and complex geological setting. Industrial plants, on the other hand, frequently treat toxic and flammable materials. This paper deals with the definition of an effective geological and geotechnical three-dimensional model of the Biferno River coastal plain in the Molise region (Italy) as a key for a quantitative assessment of real performances of strategic infrastructures. Some remarks on the site seismic vulnerability and on the regional and local geological, geomorphological and hydrogeological conditions are given. The key objective of the seismic vulnerability assessment is discussed in relation to the spatial variability of the geological and geotechnical characteristics.