Stefania Sica

Experimental Assessment of Seismic Pile-Soil Interaction

Physical modeling has long been established as a powerful tool for studying seismic pile-soil-superstructure interaction. This chapter presents a series of 1-g shaking table tests aiming at clarifying fundamental aspects of kinematic and inertial interaction effects on pile-supported systems. Pile models in layered sand deposits were built in the laboratory and subjected to a wide set of earthquake motions. The piles were densely instrumented with accelerometers and strain gauges; therefore, earthquake response, including bending strains along their length, could be measured directly. Certain broad conclusions on kinematic and inertial SSI effects on this type of systems are drawn.

Earthquake early warning for earth dams: concepts and objectives

In the geotechnical field, the risk related to slope instabilities or collapse of geotechnical structures are increasingly being faced by early warning systems, capable of: (1) predicting the incipient collapse based on the interpretation of a continuous monitoring of the structure and (2) spreading alarm promptly to reduce people exposure. Compared with structural approaches, early warning systems have two important advantages: a faster, simpler and less expensive implementation and environmental compatibility. Past experience indicates that vulnerability of earth dams is generally low under both static and seismic loading conditions. In spite of this, earth dams are characterized by a high-risk level, due to the high exposure factor. Nowadays, the application of early warning systems to dams is fully supported by the technological progress achieved in the telecommunication field, since it is possible to install and automate recordings and transmission of all physical variables significant to check dam safety: accelerations, displacements, pore-water pressures, total stresses, seepage flows. A considerable lack still arises in the predictive models for interpreting monitoring data and providing indicators on dam safety soon after a strong earthquake. The present work illustrates the basic concepts of an earthquake early warning (EEW) system for earth dams and the main features that should characterize a predictive model to such a scope. An application to a real case is finally provided, enhancing the role played by each monitored physical variable for the aims of EEW.

SEISMIC PILE-SOIL INTERACTION: EXPERIMENTAL RESULTS VS. NUMERICAL SIMULATIONS

The present analytical work discusses the outcomes of a series of 1-g shaking table experimental tests that were carried out to validate numerical models formulated for kinematic and inertial interaction effects on pile-supported systems. Towards this aim, pile models in layered sand deposits were built in the laboratory; such models were subjected to several cyclic tests and an ensemble of earthquake loading. The piles were densely instrumented with accelerometers and strain gauges; therefore, earthquake response, including bending strains along their length, could be measured directly. Different configurations were considered for the shake-table tests; the latter configurations include free-head piles and single-degree-offreedom (SDOF) systems with short and long caps at foundation level. The experimental data have been assessed accurately to estimate the period elongation of the SDOF structures, if any. Additionally, comparisons between the soil free-field response derived experimentally and advanced numerical simulations are also included. The results of the analyses show that the period elongations of the SDOF structure caused by pile-soil-interactions may be significant, thus affecting the evaluation of structural response under earthquake loading. Implications on the assessment of existing structures and the design of new ones are discussed.

Local site effects and incremental damage of buildings during the 2016 Central Italy earthquake sequence

The Central Italy earthquake sequence initiated on 24 August 2016 with a moment magnitude M6.1 event, followed by two earthquakes (M5.9 and M6.5) on 26 and 30 October, caused significant damage and loss of life in the town of Amatrice and other nearby villages and hamlets. The significance of this sequence led to a major international reconnaissance effort to thoroughly examine the effects of this disaster. Specifically, this paper presents evidences of strong local site effects (i.e., amplification of seismic waves because of stratigraphic and topographic effects that leads to damage concentration in certain areas). It also examines the damage patterns observed along the entire sequence of events in association with the spatial distribution of ground motion intensity with emphasis on the clearly distinct performance of reinforced concrete and masonry structures under multiple excitations. The paper concludes with a critical assessment of past retrofit measures efficiency and a series of lessons learned as per the behavior of structures to a sequence of strong earthquake events.

Reconnaissance of geotechnical aspects of the 2016 Central Italy earthquakes

Between August and November 2016, three major earthquake events occurred in Central Italy. The first event, with M6.1, took place on 24 August 2016, the second (M5.9) on 26 October, and the third (M6.5) on 30 October 2016. Each event was followed by numerous aftershocks. The 24 August event caused massive damages especially to the villages of Arquata del Tronto, Accumoli, Amatrice, and Pescara del Tronto. In total, there were 299 fatalities, generally from collapses of unreinforced masonry dwellings. The October events caused significant new damage in the villages of Visso, Ussita, and Norcia, although not producing fatalities, since the area had largely been evacuated. The Italy–US Geotechnical Extreme Events Reconnaissance team investigated earthquake effects on slopes, villages, and major infrastructures. The approach adopted to carry out post-earthquake reconnaissance surveys was to combine traditional reconnaissance activities of on-ground evidences and mapping of field conditions with advanced imaging and damage detection routines enabled by state-of-the-art geomatics technology. Presented herein are the outcomes of the post-event reconnaissance surveys conducted after both the August main shock and the October events, focusing on geotechnical aspects, such as earthquake-triggered slope failures, mud volcanoes, performance of different geotechnical structures (i.e., dams, retaining walls, rockfall barriers, road embankments) and building damage patterns related to site amplification.

Correction to: Reconnaissance of geotechnical aspects of the 2016 Central Italy earthquakes

Because of an error during the editorial process the first name initial of author Ernesto Ausilio was incorrectly given as A. (A. Ausilio) in the initial online publication. It should obviously be E. Ausilio. The original article has been corrected.

Soil-Structure Interaction on the Dynamic Response of Bridge Piers

The paper analyses the effect of Soil-Structure-Interaction (SSI) on the modal dynamic response of simply-supported span girder bridge with wall piers founded on caissons. A parametric analysis has been carried out in the hypothesis of linear elastic behaviour of all materials (soil and structure) to identify the influence of various design factors, such as the height of the pier, the caisson embedment below the ground level and the soil mechanical properties. The goal of the paper is to highlight SSI effects on the dynamic behaviour of bridges. This is a crucial aspect to be accounted for in order to support monitoring activities on bridges, aimed to structural identification or assessment of structure response under serviceability conditions, or also to have preliminary information for the seismic analysis of the bridge.