Dynamic characterization of fine-grained soils in Central Italy by laboratory testing
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Dynamic characterization of fine‑grained soils in Central Italy by laboratory testing Andrea Ciancimino1 · Giuseppe Lanzo2 · Giorgio Andrea Alleanza3 · Sara Amoroso4,5 · Roberto Bardotti6 · Giovanni Biondi7 · Ernesto Cascone7 · Francesco Castelli8 · Anita Di Giulio9 · Anna d’Onofrio3 · Sebastiano Foti1 · Valentina Lentini8 · Claudia Madiai6 · Giovanna Vessia5 Received: 1 October 2018 / Accepted: 2 April 2019 © Springer Nature B.V. 2019
Abstract The investigation of soil response to dynamic loads is necessary to predict site-specific seismic hazard. This paper presents the results of cyclic and dynamic laboratory tests carried out after the 2016–2017 Central Italy Earthquake sequence, within the framework of the seismic microzonation studies of the most damaged municipalities in the area. The database consists of 79 samples investigated by means of dynamic resonant column tests, cyclic torsional shear tests or cyclic direct simple shear tests. Results are firstly analysed in terms of field and laboratory values of small-strain shear wave velocity, highlighting the influence of the sample disturbance and of the mean effective consolidation pressure. The cyclic threshold shear strains as a function of plasticity index are then compared with findings from the published literature and the outliers are analysed. Subsequently, the dynamic soil behaviour is investigated with reference to the small-strain damping ratio. Differences between results from different tests are analysed in the light of the loading frequencies. Finally, the database is used to develop a predictive model for soil nonlinear curves according to plasticity index, mean effective confining stress, and loading frequency. The model represents a useful tool to predict the nonlinear stress–strain behaviour of Central Italy soils, necessary to perform site-specific ground response analyses. Keywords Soil dynamics · Laboratory tests · Shear modulus and damping ratio · Smallstrain material damping · Shear wave velocity
Communicated by S.I.: Seismic Microzonation of Central Italy. * Andrea Ciancimino [email protected] Extended author information available on the last page of the article
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Bulletin of Earthquake Engineering
1 Introduction A thorough understanding of the stress–strain behaviour of soils is crucial to perform sitespecific ground response analyses. Cyclic tests are carried out in laboratory to characterize the dynamic response of soils, that is necessary to predict the site response under seismic loading. An idealized soil response under cyclic loading is illustrated in Fig. 1 in terms of hysteretic stress–strain loop, where 𝜏 and 𝛾 are the shear stress and the shear strain, respectively, while 𝜏c and 𝛾c are the cyclic shear stress amplitude and the cyclic shear strain amplitude, respectively. The reference parameters are usually the secant shear modulus ( GS ) and the material damping ratio ( D ). At very small strains approaching zero, the secant shear modulus assumes the maximum value ( G0 ) (Fig. 1). The
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