An experimental study has been carried out using a new resonant column torsional shear cell to investigate the small strain behavior of an unsaturated compacted silty sand. The device, recently developed at the Dipartimento di Ingegneria Geotecnica di Napoli (Italy), is fitted for controlled-suction testing using the axis-translation technique. Both optimum and wet of optimum compacted specimens have been tested to analyze the effects of suction and fabric on soil behavior. Shear stiffness measurements have been taken during constant-suction tests. Collected data indicate an S-shaped initial shear stiffness versus suction variation, which can be explained considering the progressive change from a bulk-water regulated soil response to a menisci-water regulated soil response. A model is proposed to account for the observed trend. Results highlight significant effects of suction and fabric on soil behavior.Key words: compacted soil, small strain behavior, shear stiffness, suction, soil fabric.
The basic function of a gas distribution sys- tem, essentially composed of buried pipelines, reduc- tion stations, and demand nodes, is to deliver gas from sources to end users. The objective of the article is to discuss the evaluation of seismic risk of gas networks in compliance with the performance-based earthquake en- gineering framework adapted to spatially distributed sys- tems. In particular, three issues are addressed: (1) spatial seismic hazard characterization in terms of ground shak- ing and permanent ground deformation; (2) analysis of system’s vulnerability via fragility curves; (3) seismic per- formance evaluation via computer-aided simulation. As an application, the seismic risk analysis of L’Aquila (cen- tral Italy) gas distribution network, a 621-km mid- and low-pressure pipeline system was considered. The anal- yses were performed with reference to the mid-pressure part of the network, through an object-oriented software, specific for risk assessment of lifelines, developed by the authors. Results in terms of connectivity-based per- formance indicators are presented and discussed, along with a performance disaggregation analysis carried out to evaluate the contribution of the components of the sys- tem to the risk
The development of a soil shear rupture during an earthquake can occur along unstable slopes and at\ud the foundation level, for sliding failure mechanisms. This singularity in the seismic wave propagation is\ud not implemented in the common codes for one-dimensional seismic response analysis, usually including\ud linear equivalent soil models. Instead, the code developed in this study was conceived, addressed and\ud optimised to reliably model both the ‘transient’ seismic response (‘stick’ mode) and the permanent\ud deformation mechanisms accounting for the coupled effects of deformability and strength (‘slip’ mode).\ud The code models the soil profile as a system of consistent lumped masses, connected by viscous\ud dampers and springs with hysteretic non-linear behaviour. The viscous damping matrix is defined\ud according to the Rayleigh formulation. The non-linear hysteretic soil response is described by the MKZ\ud model and modified Masing rules. The shear failure is modelled through plastic sliders activating when\ud the limit shear strength is reached. The code is applied to model the behaviour of an earth dam and a\ud natural slope that have undergone significant displacements during strong-motion earthquakes; the\ud results are compared with the observations and those obtained by uncoupling the seismic response from\ud the displacement analysis by the rigid sliding block model
In this paper, we present 3D physics-based numerical simulations, in the near-source region at the regional scale, of the 2009, April 6, L’Aquila earthquake (central Italy), based on improved models of the Aterno river basin geology and source kinematics. The simulations were carried out by an open-source code, SPEED, based on a discontinuous Galerkin spectral element method. The numerical mesh of the Aterno basin was built on a detailed subsurface geological model and on the evaluation of the dynamic properties of the soils. The source model was selected among the kinematic solutions available in the literature as the one that fits best the near-source observations. Broadband ground motions were then generated through a hybrid method, combining 3D low frequency waveforms with high-frequency stochastic synthetics. To provide an example of application as seismic input to earthquake engineering analyses in the time domain, results of this approach were used for 2D site response analyses at Castelnuovo, a village severely damaged by the earthquake, and in the neighborhood of which no seismic record was available. SPEED simulation satisfactorily reproduces the recorded accelerograms in the frequency range 0.1–0.7 Hz. The site response analysis at the local scale shows that the amplification of the hill is more significant at its natural frequency, due to topographic and stratigraphic factors, than at the peak of the seismic input simulated by SPEED, that is at about 3 s along the fault-normal component. The presented application supports the conclusion that 3D physics-based numerical simulations do have the potential to become an alternative for determination of input ground motion for earthquake engineering analyses, especially for those scenarios for which real records are not available. © 2017 Springer Science+Business Media Dordrech
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