Claudia Madiai

Geotechnical Aspects of the L’Aquila Earthquake

On April 6, 2009 an earthquake (ML = 5.8 and MW = 6.3) stroke the city of L’Aquila with MCS Intensity I = IX and the surrounding villages with I as high as XI. The earthquake was generated by a normal fault with a maximum vertical dislocation of 25 cm and hypocentral depth of about 8.8 km. The deaths were about 300, the injured were about 1,500 and the damage was estimated as high as about 25 billion €. Both maximum horizontal and vertical components of the accelerations recorded in the epicentral area were close to 0.65 g. The paper summarises the activities in the field of earthquake geotechnical engineering aimed to the emergency and reconstruction issues. The ground motion recorded in the epicentral area is analysed; the geotechnical properties measured by in-situ and laboratory tests before and after the earthquake are summarised; site effects are preliminarily evaluated at accelerometric stations locations and damaged villages; the outstanding cases of ground failure are finally shown.

Shear Wave Velocity-Penetration Resistance Correlation for Holocene and Pleistocene Soils of an Area in Central Italy

With the aim of preventing and reducing the seismic risk in an area in Umbria, central Italy, of notable importance from a historic and economic point of view, the local government of the Umbria Region promoted a considerable seismic microzonation project. A widespread geotechnical investigation survey was carried out to this end, including sounding with undisturbed sampling, standard penetration tests, dynamic cone penetration tests, cone penetration tests, down-hole and cross-hole tests. The purposes of this paper are to summarise the results from field and laboratory testing performed to identify the main soil types detected in the area and to provide some empirical relations to estimate shear wave velocity from cone penetration resistance for the most representative geological formations of the region. With the aim of obtaining relationships that are as reliable as possible, the available data were carefully selected. Moreover, as it is well known that larger coefficients of determination are generally obtained when soil type, geologic age and sedimentary environment effects are considered in the regression equations, the selected data were subdivided and attributed to the two main geological units (Holocene and Pleistocene) present in the area. For each of these, grain size was classified using CPT data and two soil types (fine and coarse grained soils) were therefore identified. Regional correlations between shear wave velocity and penetration resistance parameters were thus assessed for all the four previously defined soil classes and for the two geological units without distinguishing fine-grained and coarse-grained soils. The proposed relationships were compared with those suggested in the geotechnical literature by different authors and their predictive capacity was finally checked by comparing VS values estimated by means of the correlations and those measured in geophysical survey (cross-hole and down-hole tests). The results of these comparisons are also shown in this paper.

Influence of uncorrected accelerogram processing techniques on Newmark's rigid block displacement evaluation

Design seismic motion represents a fundamental issue of many geotechnical applications. In more complex numerical procedures, input motion is required in the complete form of an accelerogram, whereas in simplified prediction methods it is generally expressed by means of synthetic parameters such as peak ground acceleration, peak ground velocity, Arias intensity, etc. The aim of this paper is to show the sensitiveness of these parameters to small changes in the characteristics of the accelerogram associated with the filtering procedures used for reducing digitisation errors, instrument distortions, etc. and the influence of the consequent uncertainties on geotechnical applications. More specifically this paper examines the incidence of processing techniques of uncorrected records from Italian accelerograph network on slope displacement evaluation based on Newmarks rigid block model.

CPT-Based Liquefaction Case History from the 2012 Emilia Earthquake in Italy

AbstractSignificant and widespread liquefaction phenomena were observed after the main shock of the Emilia earthquake (Italy) on May 20, 2012. A considerable number of surveys were subsequently performed to accurately test the susceptibility to liquefaction of soil deposits affected by the most severe liquefaction-induced effects and damage. Ground surface morphology was defined in detail by means of LIDAR survey results; subsoil stratigraphy and water table level were inferred from CPT tests and soundings; physical properties and mechanical parameters of soils were obtained from laboratory tests or indirectly inferred from the results of a large number of CPT tests carried out in the area. Two main sandy layers susceptible to liquefaction were identified and appropriately characterized. Seismic loading induced by the main shocks of the sequence was carefully estimated from the peak ground acceleration map produced by the National Institute of Geophysics and Volcanology. More than 90 sites were examined i...

Soil Liquefaction During the Emilia, 2012 Seismic Sequence: Investigation and Analysis

In the framework of a Project issued by the Italian National Institute of Geophysics and Volcanology (INGV) a Research Unit (RU) has been granted with the commitment to provide a link between the seismic shaking and the triggering of ground failures such as liquefaction. The main goals have regarded both the enlargement of the base of observables for a better constrain of the seismic hazard assessments and the analysis of the triggering and causative factors of permanent ground deformations. Nevertheless, when analyzing the non-linear soil response under which liquefaction occur, some insights into site-effects have been also provided, thus contributing to the general task of the site-specific hazard. The paper illustrates the analyses and investigations carried out within the aim of the project, some of them are still provisional due to the huge amount of data produced and the strong effort required to analyze all the matters related to the observed phenomena.

A Methodology for Advanced Seismic Microzoning Using 2D Analyses: The Case Study of Barberino di Mugello, Florence, Italy

The here presented study was developed in the frame of the VEL/DOCUP projects promoted by the Regional Government of Tuscany (Central Italy) in order to mitigate the risk from earthquake. It concerns the assessment of local seismic effects aimed at drawing up a detailed seismic microzoning map for an area including some villages, industrial and commercial settlements close to the most important town of western Mugello, one of the highest seismicity zones of the Northern Apennine Chain. Geological subsoil modelling and geotechnical characterization of the area under study were performed by using the results of an in-depth survey including in situ and laboratory tests. On the basis of geomorphologic and lithostratigraphic data, a first level of seismic zoning map was prepared aimed to recognize areas involved in different kinds of geotechnical phenomena (amplification, slope-instability, liquefaction, etc.) and several representative cross sections were then identified for the whole area under study. Numerical 2D analyses were implemented on the selected cross sections to quantify the local seismic response on ground surface. The performed analyses allowed to recognize zones with different seismic response in term of a suitable selected amplification factor and to draw a Level 3 seismic microzonation map according to the procedure recommended by the Italian guidelines for microzoning. In this paper the results of two-dimensional local seismic response analyses and advanced seismic microzonation mapping for the area under study are presented and discussed.

Soil Liquefaction Analyses in a Test-Area Affected by the 2012 Emilia-Romagna Earthquake (Italy)

Significant and widespread liquefaction effects were observed in the area of San Carlo and Mirabello villages during the Emilia-Romagna earthquake of May 20 and 29, 2012. After the earthquake, an intensive program of laboratory and in situ (mostly CPT’s) tests was carried out in the affected area. The stratigraphic and geotechnical conditions have been found to predispose the soil deposits to liquefaction phenomena. The triggering conditions, i.e. the design earthquake parameters, have been evaluated according to the most recent seismic hazard analyses and local seismic response analyses. The liquefaction risk, expressed in term of liquefaction potential index (LPI), was determined by using the CPT-based simplified method of Robertson and Wride. The obtained results are not consistent with the observed liquefaction effects and the liquefaction risk seems to be systematically underestimated. In the present paper the reason of this underestimation is investigated and a possible correction for applying the simplified cyclic stress approaches is proposed.

Influence of Soil Dynamic Parameters on Seismic Response of a Site at Fabriano, Italy

1 Dipartimento di Ingegneria Civile, Universita di Firenze, Italy – teresa@dicea.unifi.it 2 Dipartimento di Ingegneria Strutturale e Geotecnica, Politecnico di Torino, Italy diego@geohp.polito.it 3 Dipartimento di Ingegneria Civile, Universita di Firenze, Italy 4 Dipartimento di Ingegneria Civile, Universita di Firenze, Italy INFLUENCE OF SOIL DYNAMIC PARAMETERS ON SEISMIC RESPONSE OF A SITE AT FABRIANO, ITALY

Seismic Stability Analyses of the Po River Banks

The Po River is the major Italian watercourse. Over half its length is controlled with embankments as protection measures against heavy floodings. Recently, the Italian Government has funded a project for the evaluation of the seismic stability of about 90 km of embankments of the Po River. The project mainly aims at the seismic stability analyses of the river banks, with assessment of local site response and evaluation of the liquefaction potential. Hundreds of geotechnical investigations within the study area were performed and the water level variations in the embankment and subsoil were investigated using piezometers. This paper describes the methodology and the main results of the analyses. The safety of 43 significant sections in static and seismic conditions was investigated using limit equilibrium analyses. Dynamic effects in the seismic condition were considered using the pseudostatic method. Local seismic hazard and effects of site conditions on the ground motion are taken into account in the definition of the expected seismic action. Eventually, the analysis results are summarized in a static and seismic stability map of the investigated area, a useful tool for the local Authority in the prevention and mitigation.

Local Seismic Response Prediction and Design Building Code Provisions : The Case Study of Senigallia, Italy

With the aim to contribute to the discussion on the validation of European and Italian design building code spectra, this paper describes and discusses the results obtained by means of equivalent linear analyses performed in a number of well documented test sites located alongside the Adriatic coast, in the town of Senigallia, Central Italy. Given the medium intensity shaking expected in the area (peak ground acceleration of 0.20g at ‘rock-like’ formation with a return period of 475 years) and the likely strain levels that can be induced on soils, and also given the geomorphologic characteristics of the site (mainly consisting of a Plio-Pleistocene clayey-marly bedrock underlying Quaternary plain deposits and alluvial terraces where 2-D effects appear to be not influent) a 1-D linear equivalent model was employed for seismic site response evaluation. The seismic response analyses were performed on eight different soil profiles where dynamic soil properties were accurately measured. In order to reduce the input seismic ground motions uncertainties Both real selected acceleration time histories and simulated accelerograms obtained by a seismic wave propagation model were assumed in the analyses,. The obtained results are synthesised in this paper and the elastic response spectra obtained at ground surface are compared with those provided by Eurocode 8 for the corresponding ground types. The practical significance, implications and applications of the spectra obtained with respect to the relevant prescriptions of the recently established Italian building codes for seismic areas are also discussed. RÉSUMÉ Afin de contribuer à la discussion sur la validation des Eurocodes et des règlements parasismiques italiens pour les bâtiments, cet article se propose de montrer et d’examiner les résultats d’analyses de la réponse sismique locale menées par un modèle 1-D linéaire équivalent dans un certain nombre de ‘test sites’ bien documentés qui se trouvent le long de la côte adriatique, dans la ville de Senigallia (Italie centrale). En considérant aussi bien l’intensité moyenne-basse du séisme attendu dans la zone étudiée (pic d’accélération 0.20g sur formation rocheuse pour une période de retour de 475 ans) que les caractéristiques géomorphologiques du site, consistant principalement d’une Plio-Pléistocène roche-substratum marno-argileuse située en dessous de dépôts de plaine alluviale et de terrasses étagées où les effets 2-D n’ont pas d’influence, les analyses de la réponse sismique locale ont été menées par un modèle 1-D linéaire équivalent. L’étude a été effectué sur onze verticales où les propriétés dynamiques du terrain ont été soigneusement mesurées. Afin de limiter les incertitudes liées à la donnée sismique, on a employé des enregistrements sismiques réels comme des signaux sismiques simulés. Dans cet article sont présentés les résultats numériques des analyses; les spectres de réponse obtenus sont confrontés aux spectres établis par l’Eurocode 8 et par les récents règlements parasismiques italiens pour les correspondants types de sous-sol.