Filippo Santucci de Magistris

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).

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.

One-Dimensional Ground Response as a Preliminary Tool For Dynamic Analyses in Geotechnical Earthquake Engineering

This article discusses how to calibrate some parameters of two-dimensional finite element models for numerical analyses in geotechnical earthquake engineering. The calibration was made through the simulation of the one-dimensional vertical propagation of S-waves in elastic layers, whose theoretical solutions are available in literature. The numerical results were compared with those obtained by frequency domain analyses. The influence of several sources of damping arising in the model, including that deriving from boundary conditions and numerical integration, was investigated. The proposed calibration procedure constitutes a useful preliminary step for performing advanced dynamic analyses of any geotechnical system.

The Influence of Meso-Structure on the Mechanical Behaviour of a Marly Clay from Low to High Strains

On October 31, 2002, a ML=5.5 earthquake struck the Molise region in Southern Italy. The strongly non-uniform damage distribution observed in the town of San Giuliano di Puglia suggested that site amplification significantly affected the seismic response of the Toppo Capuana marly clay formation.

An Integrated Seismic Monitoring System for a Full-Scale Embedded Retaining Wall

Over the last 50 years, data from laboratory tests and post-earthquake reconnaissance have been used to gain knowledge about the dynamic and seismic behavior of geotechnical structures and to improve analysis and design procedures. The scarcity of reconnaissance data has pointed out the need for full-scale and near full-scale tests for research purposes in earthquake engineering. Structural health monitoring (SHM) systems have been applied to different kinds of structures, but although static control of displacements and pressures is quite common, dynamic monitoring is fairly limited in geotechnical engineering. In the present paper, an integrated structural and geotechnical monitoring program aimed at filling this knowledge gap is described with reference to a real flexible retaining wall. The objective of the research is to establish a combination of sensors, numerical analyses, and data processing procedures to turn the monitored retaining wall into a smart geotechnical structure. Attention is herein focused on two aspects related to the implementation of the monitoring system and the dynamic identification of the soil-structure system. Specifically, the paper describes an example of seismic monitoring system for full-scale flexible retaining walls based on sensors embedded in the reinforced concrete piles. Installation details are given together with a description of the monitoring system architecture in its current stage of implementation. Issues and requirements for the measurement chain are discussed, taking into account possible installation drawbacks (i.e., shocks) and the opportunity to monitor the response under operational conditions. Furthermore, a novel and successful application of operational modal analysis (OMA) to such a complex geotechnical system is reported. It allows for the identification of the fundamental modes of the soil-wall system in operation (but before the erection of a building on the excavated side). Implementation of the monitoring system prototype is still in progress, but some interesting results have already been outlined.

Lessons learned from two case histories of seismic microzonation in Italy

The prediction of the variability of the seismic ground motion in a given built-up area is considered an effective tool to plan appropriate urban development, to undertake actions on seismic risk mitigation and to understand the damage pattern caused by a strong-motion event. The procedures for studying the seismic response and the seismic microzonation of an urban area are well established; nevertheless, some controversial points still exists and are discussed here. In this paper, the selection of a reference input motion, the construction of a subsoil model and the seismic response analysis procedures are discussed in detail, based on the authors’ experience in two Italian case histories: the seismic microzonation of the city of Benevento, which was a predictive study, and the simulation of seismic response and damage distribution in the village of San Giuliano di Puglia, which was a retrospective analysis.

Dependency of the Mechanical Behaviour of Granular Soils on Loading Frequency: Experimental Results and Constitutive Modelling

The paper shows some cyclic torsional shear test results obtained on dense Toyoura sand specimens. The dependency of the mechanical response of this material on both loading amplitude and frequency are discussed, to obtain a framework to analyze the mechanical behaviour of granular soils. The pseudo-elastic shear stiffness and the damping ratio are the variables taken into consideration; their evolution with the number of cycles performed at the different loading amplitudes is analysed to describe the mechanical irreversibility of the material response.

Earthquake Triggered Landslides: The Case Study of a Roadway Network in Molise Region (Italy)

In this paper, a level II approach aimed at evaluating the impact of the triggering potential of seismic landslides on a regional roadway network is described. The case study is located within the Southern Apennines in Molise Region (Italy). A seismic vulnerability assessment through fragility curves was performed. Its capability to provide useful data in view of territory planning and/or emergency management was explored by means of the implementation in GIS environment.

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.

Some Limits in the Use of the MASW Technique in Soils with Inclined Layers

Abstract The surface wave method is a characterization technique that allows obtaining the shear wave velocity profiles trough the measurement of the dispersion of surface waves coupled with an inversion procedure. Spectral and multichannel analysis of surface wave techniques are becoming, recently, a common investigation tool for site characterization. For the inversion of the surface wave dispersion curve, homogeneous or horizontally layered soil models are assumed and this hypothesis could represent a limitation on the practical use of the technique. In this paper, the numerical dispersion curves of a subsoil, constituted by two layers of elastic material separated by a horizontal or an inclined interface, are simulated by a finite element commercial code. This allows detecting some limits in the conventional interpretation of the surface wave tests. MASW experiments executed in two different sites in Molise Region (Italy), characterized by simple or complex stratigraphic conditions, are shown as examples to validate the assumption and the analyses made in the paper.