Michele Maugeri

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.

Seismic stability of retaining walls with surcharge

Abstract The use of pseudo-static methods for the computation of soil thrust acting on retaining walls under seismic condition is well established in the design of such structures. Although different methods, based on the limited displacement concept, have been developed in the last 20 years, the most common design method is still the method derived from the theory developed by Mononobe and Okabe. However, the Mononobe–Okabe method presents a basic shortcoming: the solution is based on the limit equilibrium of the soil wedge without taking into account the presence of the wall. In the paper a new solution based on the pseudo-static equilibrium of the soil–wall system is presented. The developed solution takes into account the effect of the presence of the wall and it is applied to soil–wall systems with surcharged backfills. Formulas are provided to calculate directly the yield acceleration and the inclination of the failure surface. The effect of the intensity of the surcharge and of its distance from the wall is investigated and the results are compared to those obtained in the case of soil–wall systems without surcharge.

Experimental study in the shaking table of the input motion characteristics in the dynamic SSI of a SDOF model

In conventional seismic design the capacity of the system is generally exploited only at the superstructure level. However, soil non-linearity as well as soil-foundation interface non-linearity can be crucial in the seismic response of structures. The results of tests performed on physical models allow the main aspects of these interaction mechanisms to be identified and also provide a benchmark for subsequent theoretical or numerical analyses. The present paper deals with two shaking table tests performed at the University of Bristol’s EERC laboratory. The tests were performed on a physical model consisting of a Leighton Buzzard sand deposit and a one-storey steel model structure. Some of the test results are presented and discussed in terms of acceleration and displacement responses. Both time- and frequency-domain representations were adopted to highlight the influence of the frequency and amplitude of the input motion on the coupled and/or uncoupled response of the tested soil-structure system, as well as the effect of soil non linear behaviour.

Flow and deformation failure of sandy slopes

The effects of earthquake induced pore pressure on seismic and post seismic stability conditions of cohesionless slopes are investigated with reference to the infinite slope scheme. In cohesionless slopes the shear strength reduction caused by pore pressure build-up may lead the slope to a deformation failure or to a flow failure if liquefaction conditions are approached. Two critical values of the seismic induced pore pressure ratio are introduced to evaluate the effect of shear strength reduction on the slope failure mechanism. The results are given in the form of stability charts and a procedure for the evaluation of the seismic stability condition is described. The procedure gives useful information about the failure mechanism that slopes may exhibit and the displacement analysis which should be carried out.

The Seismic Microzonation of the City of Catania (Italy) for the Etna Scenario Earthquake (M = 6.2) of 20 February 1818

Based on the seismic history of the city of Catania (Italy), the Etna earthquake of 20 February 1818 (IMCS = VIII–IX, MS = 6.2) has been considered as an earthquake scenario. Despite its lower magnitude, the Etna 1818 earthquake can be accounted for in the seismic hazard assessment of Catania, since it may cause heavy damage to the city. The epicenter was located along the southeastern flanks of the Etna Volcano, close to the municipal area of the city of Catania. The ground-response analysis at the surface has been obtained by one-dimensional (1-D) nonlinear models. According to the response spectra obtained through the application of the nonlinear models, the city of Catania has been divided into zones with different peak ground acceleration at the surface. A ground-shaking map for the urban area of the city of Catania was generated via GIS for the 1818 earthquake scenario.

Site effects and site amplification due to the 2009 Abruzzo earthquake

This paper presents the results of numerical analyses carried out to assess the different seismic response of two sites in the urban area of L’Aquila, selected as representative of typical subsoil conditions in the old city centre and in the recently developed suburban Pettino district. Both areas were severely damaged by the April 6, 2009 earthquake. The geotechnical model of the subsoil at each of the two sites and the related parameters, defined based on accurate site investigations, are described. The comparison of results of seismic response analyses at the two sites, in agreement with strong motion recordings of the April 6, 2009 main shock, confirms that site effects due to different subsoil conditions played an important role in the observed non-uniform damage distribution. Particularly in the city centre, characterized by an inversion of the shear wave velocity VS with depth, the simplified approach based on elastic response spectra defined according to ground type (VS,30) of the Italian building code tends to underestimate the seismic action and should be used with caution.

Seismic response in Catania by different methodologies

The prediction of the seismic response and assessment of the amplification factor of the surface soils is a topic of maximum interest in engineering seismology and the final goal of any microzonation study. Two very different numerical techniques are described in this paper. One is a 2-D method, the Spectral Element Method (SPEM-2D), which solves the propogation of the seismic field through complex geological structures. The other is a 1-D method (by the GEODIN code), commonly used in engineering practice, which takes into account the detailed shear waves soil profile or superficial layers, including soil non-linearity. The seismic response of the surface by 1-D code is evaluated, using as input motion at the conventional bedrock sealed recorded accelerograms and synthetic accelerograms given by the 2-D code at a given depth. A comparison between soil response at the surface, given by the 2-D method, and by the 1-D method is presented in the paper. In particular the effects of the seismic input, of the shear waves soil profile and of the soil non-linearity, are also analyzed and discussed.

Numerical analysis of kinematic soil—pile interaction

In the present study, the response of singles pile to kinematic seismic loading is investigated using the computer program SAP2000@. The objectives of the study are: (1) to develop a numerical model that can realistically simulate kinematic soil‐structure interaction for piles accounting for discontinuity conditions at the pile‐soil interface, energy dissipation and wave propagation; (2) to use the model for evaluating kinematic interaction effects on pile response as function of input ground motion; and (3) to present a case study in which theoretical predictions are compared with results obtained from other formulations. To evaluate the effects of kinematic loading, the responses of both the free‐field soil (with no piles) and the pile were compared. Time history and static pushover analyses were conducted to estimate the displacement and kinematic pile bending under seismic loadings.

One-dimensional Seismic Analysis of a Solid-Waste Landfill

Analysis of the seismic performance of solid waste landfill follows generally the same procedures for the design of embankment dams, even if the methods and safety requirements should be different. The characterization of waste properties for seismic design is difficult due the heterogeneity of the material, requiring the procurement of large samples. The dynamic characteristics of solid waste materials play an important role on the seismic response of landfill, and it also is important to assess the dynamic shear strengths of liner materials due the effect of inertial forces in the refuse mass. In the paper the numerical results of a dynamic analysis are reported and analysed to determine the reliability of the common practice of using 1D analysis to evaluate the seismic response of a municipal solid‐waste landfill. Numerical results indicate that the seismic response of a landfill can vary significantly due to reasonable variations of waste properties, fill heights, site conditions, and design rock motions.

Seismic response of saturated cohesionless slopes

Abstract The serviceability of a slope after an earthquake is controlled by deformations, consequently a stability analysis that predicts slope displacements is desirable. In cohesionless satured slopes the seismic loading may produce an increase in pore pressures, which in turn, reduces significantly the effective state of stress. Depending on the seismic intensity and on the effective stress conditions before the seismic loading, the induced excess pore pressures may produce the slope failure. Slope displacements may occur even for seismic accelerations lower then the initial critical acceleration, because of pore pressure build-up. In this paper, a simplified procedure for the seismic response of infinite slopes is described, and the role-played by relevant parameters such as soil relative density and initial pore pressure ratio is pointed out.