Armando Lucio Simonelli

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.

Experimental Investigation of Dynamic Behavior of Cantilever Retaining Walls

The dynamic behaviour of cantilever retaining walls under earthquake action is explored by means of 1-g shaking table testing, carried out on scaled models at the Bristol Laboratory for Advanced Dynamics Engineering (BLADE), University of Bristol, UK. The experimental program encompasses different combinations of retaining wall geometries, soil configurations and input ground motions. The response analysis of the systems at hand aimed at shedding light onto the salient features of the problem, such as: (1) the magnitude of the soil thrust and its point of application; (2) the relative sliding as opposed to rocking of the wall base and the corresponding failure mode; (3) the importance/interplay between soil stiffness, wall dimensions, and excitation characteristics, as affecting the above. The results of the experimental investigations were in good agreement with the theoretical models used for the analysis and are expected to be useful for the better understanding and the optimization of earthquake design of this particular type of retaining structure.

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.

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.

Soil-Pile-Structure Interaction Evidences from Scaled 1-g model

The seismic soil-pile-structure interaction (SPSI) is a complex mechanism that is usually considered formed by the combination of kinematic and inertial interaction. Both mechanisms generate additional forces on the system related to the stiffness contrast between the soil and the foundation for the kinematic interaction and to the soil response around the foundation due to the inertial contribution of the superstructure for the so-called inertial interaction. While the mechanism of each of these contributions is clear, their combination is still under investigation due to number of parameters involved (i.e. dynamic characteristics of both system and input). An effective way to study this combination is the analysis of actual data on real structures. Due to the fact that these data are hard to find, usually the response of physical scaled models on 1-g and n-g devices are investigated. In this connection, this paper presents some results from an extensive 1-g shaking table testing activity. The scaled physical model is formed by a group of five piles embedded in a by-layer deposit of dry sands with an oscillator connected to the piles through different kind of foundation systems. More specifically, the attention is focused on both pile and structural response when the oscillator is connected to a small group of three piles by means of a stiff foundation. The analysis of the experimental data enhances the role of the resonance between the soil-structure system and the input waves in the general behavior of both structure and piles.

NUMERICAL SIMULATION OF SOIL-STRUCTURE INTERACTION: A PARAMETRIC STUDY

Soil Structure Interaction (SSI) is a complex phenomenon that may radically change the earthquake response of structural systems, as consequence of the variation of the natural frequency and the damping ratio. One of the most effective means for evaluating SSI is the use of physical models. In this study the physical model considered is formed by an oscillator founded on a group of piles embedded in a horizontally layered deposit of dry sand. The benchmark experimental campaign was carried out at the Bristol Laboratory for Advanced Dynamics Engineering (BLADE) at the University of Bristol (UK), financed by the Seismic Engineering Research Infrastructures for European Synergies (SERIES). An accurate parametric numerical study is performed and the results are discussed. The study investigates the effects of the dynamic properties of the oscillator on the period elongation and piles response. By means of advanced numerical analyses the outcomes of the present work provide insights into the quantitative evaluation of period elongation and the strength of inertial contribute to the bending moment at the pile head, when the system approaches resonance conditions. 3568 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 3568-3577

SOIL-PILE-STRUCTURE-INTERACTION: EXPERIMENTAL RESULTS AND NUMERICAL SIMULATIONS

The complex seismic soil-pile-structure interaction phenomenon is related to the interaction between foundation and structure under seismic and dynamic excitations. An ef- fective way to assess such phenomenon is to analyse the response of scaled physical model in 1-g or n-g devices. In this study some results selected from a comprehensive 1-g shaking table tests are reported and discussed. The extensive experimental campaign was carried out on the 3mx3m shaking table of the Bristol Laboratory for Advanced Dynamics Engineering (BLADE) at the University of Bristol (UK), within the framework of the Seismic Engineering Research Infrastructures for European Synergies (SERIES). The physical model comprises a pile group embedded in a by-layer soil deposit with different pile configurations. This paper focuses on the pile group response generated by the presence of a cantilever system (a single-degree-of- freedom, SDOF) connected at the top of the central pile considering no connection among the other pile heads. The selected input motions consist of a set of sinedwell excitations for SDOFs with different structural masses. The experimental data are used to validate an ad- vanced 2D difference element model using the FLAC2D code. The comparisons between the experimental and the numerical results are presented in terms of both envelope and time his- tories for the free-field and piles responses. The SDOF response is also assessed in terms of displacement time histories. Comparisons between the numerical and experimental test re- sults appear satisfactory; hence numerical approach can be used for further simulations of the soil-pile-structure interaction phenomena.

EXPERIMENTAL INVESTIGATION OF DYNAMIC BEHAVIOUR OF CANTILEVER RETAINING WALLS

The dynamic behaviour of cantilever retaining walls under earthquake action is explored by means of 1-g shaking table testing, carried out on scaled models at the Bristol Laboratory for Advanced Dynamics Engineering (BLADE), University of Bristol, UK. The experimental program encompasses different combinations of retaining wall geometries, soil configurations and input ground motions. The response analysis of the systems at hand aimed at shedding light onto the salient features of the problem, such as: (1) the magnitude of the soil thrust and its point of application; (2) the relative sliding as opposed to rocking of the wal land the corresponding failure mode; (3) the importance/interplay between soil stiffness, wall dimensions, and excitation characteristics, as affecting the above. The results of the experimental investigations are in good agreement with the theoretical models used for the analysis and are expected to be useful for the better understanding and the optimization of earthquake design of this type of retaining structure.