726 research outputs found
Development of an advanced geostatistical model for shear wave velocity profiles to manage uncertainties and variabilities in Ground Response Analyses
No full textL'abstract è presente nell'allegato / the abstract is in the attachmen
RELIABILITY OF SOIL POROSITY ESTIMATION FROM SEISMIC WAVE VELOCITIES
No full textSoil porosity is a state parameter of fundamental importance for several geotechnical problems. Geophysical testing provide appealing strategies for the determination of soil porosity, as several geophysical parameters are directly related to soil porosity. In particular the theory of wave propagation in saturated porous media, developed by Biot in the 1950s, allows the determination of soil porosity from the measured velocity of propagation of compressional and shear waves. A formal assessment of the reliability of the estimated porosity values is of primary importance to evaluate the applicability of this approach to solve practical geotechnical problems. In this paper the propagation of measurement uncertainties on the estimated values of soil porosity is theoretically evaluated. Moreover, experimental data of multiple acquisitions of cross-hole tests are considered. Data collected by different operators are also used to assess the confidence interval associated to different equipment, acquisition practices and testing methodology
INFLUENZA DELLE INCERTEZZE NELLA VALUTAZIONE DEI PROFILI DI Vs SULLE ANALISI DI RSL: IL CASO STUDIO DI FONTE DEL CAMPO (RI)
No full textLa valutazione delle incertezze nei parametri e la loro propagazione all'interno degli studi di risposta sismica locale rappresentano un carattere fondamentale nella valutazione del rischio sismico e nella microzonazione del territorio. Il profilo delle velocità delle onde di taglio (Vs), in particolare, rappresenta il parametro chiave per descrivere il comportamento del deposito sia per bassi, che per alti livelli deformativi. La valutazione della pericolosità di un sito specifico, pertanto, deve tenere in conto di tali incertezze a livello probabilistico, in modo da fornire un risultato consistente con lo studio probabilistico di base, e che tenga conto di diversi livelli di nonlinearità
Reliability and Accuracy of Seismic Tests in Geotechnical Site Characterization
No full textGeophysical surveys, and specifically seismic tests, provide powerful tools for geotechnical site
investigation. Indeed, they cover the whole range of soils and rocks, independently of particle size, and
provide data in the natural state for the characterization at different scales. Assessment of the reliability of
the most popular techniques is therefore of primary importance for static and seismic applications. This
chapter reports some data from recent experiments devoted to reliability assessment at some reference
sites, where intra-method and inter-method variability has been studied. The propagation of the measured
uncertainties in soil porosity assessment and seismic ground response analyses is also considered to
provide an insight on the consequences in the practice of geotechnical engineering
MODELLI GEOSTATISTICI PER LA VALUTAZIONE DELLE INCERTEZZE E DELLE VARIABILITA’ NEI PROFILI DI Vs
No full textIl parametro meccanico fondamentale per la valutazione della risposta sismica locale è il profilo di velocità delle onde di taglio (VS). Esso è valutabile attraverso tecniche geofisiche sperimentali in situ, le quali presentano caratteristiche tecniche ed assunzioni teoriche differenti.
Nell’ambito di queste tecniche di indagine sperimentali, una valutazione delle incertezze e delle variabilità associate al processo di misura rappresenta una necessità indispensabile, soprattutto alla luce dei moderni approcci di valutazione non ergodica della risposta sismica locale. Per rispondere a tale esigenza, si utilizzano modelli geostatistici, i quali hanno la potenzialità di fornire un “quadro” delle incertezze epistemiche e variabilità aleatorie in gioco, tramite una randomizzazione.
L’unico modello geostatistico disponibile per tali applicazioni fu sviluppato da Gabriel Toro nel 1995. Esso rappresenta un tentativo di fornire uno strumento valido per la randomizzazione dei profili di VS ed è utilizzato in tutto il mondo per studi di pericolosità sismica, anche di edifici strategici. Il modello è stato implementato nel software STRATA e, più recentemente, nell’ultima versione del software DEEPSOIL.
La presente nota vuole inizialmente presentare le nozioni generali alla base del modello di Toro, valutando criticamente i vari elementi che lo compongono. Successivamente, verrà proposta una nuova implementazione rigorosa ed innovativa del modello, dotata di potenzialità maggiori rispetto alle versioni ad oggi disponibili. In particolare, il modello implementato è caratterizzato da un cambiamento radicale riguardante le ipotesi e l’idea alla base del processo di randomizzazione. Infatti, la novità principale riguarda il superamento dell’assunzione della velocità intervallare come variabile aleatoria principale, scomponendo il problema nelle due variabili aleatorie indipendenti alla base del processo di misura: la distanza ed il tempo
Geostatistical models for the assessment of the influence of shear wave velocity uncertainty and variability on ground response analyses
No full textA robust assessment of the influence of epistemic uncertainties and aleatory
variabilities on ground response analyses is a fundamental requirement for modern probabilistic
seismic hazard analyses. The study of epistemic uncertainties and aleatory variabilities should
follow three sequential steps: identification, quantification, and management (IQM procedure).
A fundamental input for ground response analyses is the shear-wave velocity (VS) profile. The
VS profile can be obtained via various types of geophysical tests. Each test has specific characteristics.
For these reasons, a consistent IQM procedure must be established to assess the type
and amount of uncertainties involved in the measurements, also addressing the peculiarities of
the investigated site. We propose a geostatistical model for the management of the uncertainties
included in the VS profiles obtained with surface wave tests. The model is based on the separate
randomization of travel times and layer thicknesses. It generates profiles that are consistent with
the measured “site signatures” such as the Rayleigh wave dispersion curve and the predominant
site period. The model can be easily generalized for other geophysical tests
Influence of Strong Motion Records Characteristics on Numerical Simulations of Soil Liquefaction
No full textThe selection of the appropriate input motion plays a crucial role in advanced numerical simulations of cyclic liquefaction. In the present paper, a numerical model validated against the evidence of soil liquefaction phenomena observed during the Emilia 2012 earthquake in Italy is used to assess the influence of the ground motion selection process. The numerical model has been developed using the finite element code OpenSees and adopting the pressure dependent elasto-plastic multi-yield constitutive model for the liquefiable layers. The model has been first calibrated by using laboratory and in situ tests from the San Carlo site. Then a large set of strong motion records has been used and results have been classified based on liquefaction occurrence. The most influent parameters for design purposes have been identified through a cluster analysis. The results underline that the selection criterion should be based on the estimation of expected ground motion parameters rather than on a pure spectral matching criterion
Uncertainties and variabilities in seismic ground response analyses
No full textGround response analyses (GRAs) represent a key element for the nonergodic
(site-specific) evaluation of the seismic hazard. In this respect, epistemic uncertainties
and aleatory variabilities need to be properly identified, quantified, and managed to
obtain consistent estimates. Several collaborative efforts have been carried out in recent
years to assess the influence of uncertainties and variabilities in the GRA parameters
through benchmark studies. Specifically for site characterization, efforts are required to
guarantee a sufficient quality of in situ and laboratory tests. However, benchmark tests
have shown the existence of a certain level of “uncompressible uncertainty”. Stochastic
models implemented in GRAs are therefore required to evaluate the impact of uncertainties
and variabilities on the computed seismic hazard. Such models are to be based on large
databases of experimental data to produce consistent estimates. Examples will be provided
with a specific focus on geophysical tests for the evaluation of shear wave velocity models,
which are likely the most influent parameters in GRAs
Iscrizioni greche e latine del Museo Nani in un inedito manoscritto di Giovanni Battista Passeri
No full textThis paper examines an unpublished manuscript by Giovanni Battista Passeri, kept in the Oliveriana Library in Pesaro, in which the author drew and commented Greek and Latin inscriptions from the Venetian collection of the Nani di San Trovaso, now dispersed. Along with the publication of new instrumentum domesticum inscriptions, this article highlights the significance of the manuscript and places the work of Giovanni Battista Passeri in the context of the antiquarian tradition of the time
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