Terrestrial laser scanning for rockfall stability analysis in the cultural heritage site of Pitigliano (Italy)

Traditional surveying methods are often not sufficient to achieve a complete geomechanical characterization of the rock mass, to analyze the instability mechanisms threatening the cultural heritage of hilltop historic towns. In Pitigliano (Tuscany, Central Italy), terrestrial laser scanning was employed complementarily to conventional geomechanical techniques. The overall 3D survey of the exposed surfaces was combined with scanlines of the inner walls of the subterranean cavities running underneath the historic centre. The rock mass discontinuities geometry was extracted, and the most critical instability mechanisms were mapped, with particular interest in the potential impacts on the ancient buildings located along the cliff edge. The geomechanical analysis of the surveyed joint sets confirmed a structural control on the cliff morphology by two main joint sets. Thanks to the laser scanner-based kinematic analysis, flexural toppling and wedge failure were found as the main hazardous instability mechanisms in Pitigliano. Finally, the conservation criticalities were identified and a pilot monitoring system was installed in a sector highly susceptible to block detachment.     

Modal analysis of pile‐supported structures during seismic liquefaction

The purpose of this paper is to investigate the effects of liquefaction on modal parameters (frequency and damping) of pile‐supported structures. Four physical models, consisting of two single piles and two 2 × 2 pile groups, were tested in a shaking table where the soil surrounding the pile liquefied because of seismic shaking. The experimental results showed that the natural frequency of pile‐supported structures may decrease considerably owing to the loss of lateral support offered by the soil to the pile. On the other hand, the damping ratio of structure may increase to values in excess of 20%. These findings have important design consequences: (a) for low‐period structures, substantial reduction of spectral acceleration is expected; (b) during and after liquefaction, the response of the system may be dictated by the interactions of multiple loadings, that is, horizontal, axial and overturning moment, which were negligible prior to liquefaction; and (c) with the onset of liquefaction due to increased flexibility of pile‐supported structure, larger spectral displacement may be expected, which in turn may enhance P‐delta effects and consequently amplification of overturning moment. Practical implications for pile design are discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Short-term,linear, and non-linear local effects of the tides on the surface dynamics in a new,high-resolution model of the Mediterranean Sea circulation

Ocean Dynamics - The tides in the Mediterranean Sea are generally weaker than in other regions of the world ocean, but are locally intensified in passages with complex bathymetry, such as the...     

Geochemical changes at the Bagni di Triponzo thermal spring during the Umbria-Marche 1997–1998 seismic sequence

After the earthquakes of September 26, 1997, that hit the Umbria-Marcheboundary (Apennine, Central Italy), with a maximum 6.0 M_w, aprogram of geochemical surveying together with a collection ofhydrogeological changes episodes was extended throughout theepicentre-area, taking the yearly period of the seismic sequence as a whole.After a first areal screening, the Bagni di Triponzo thermal spring wasselected for a discrete temporal monitoring (weekly and monthly basis),being the unique thermal spring throughout the epicentre area. This sitedeserves peculiar interest in deepening the knowledge about deep fluidscirculation changing during seismicity.Laboratory and on-field analyses included major, minor and trace elementsas well as dissolved gases (He, Ar, CH₄, CO₂, H₂S,²²²Rn, NH₄, As, Li, Fe, B, etc...) and selected isotopic ratios(C, H, O, He, Sr, Cl), meaningful from tectonic point of view.The chemistry and isotopic chemistry of the spring were fully outlined anddiscussed, pointing out the main process involving the thermal aquifer: thewater-rock interaction inside the Evaporite Triassic Basement (ETB),possibly involving also the Paleozoic Crystalline Basement. On theother hand, sudden and apparent geochemical and hydrogeologicalvariations during the seismic sequence ruled out an evolution in thewater-rock interaction processes. They occurred both at depth, i.e.,induced by fluid remobilization within the crust explained by the Coseismic Strain Model and by the Fault Valve Activity Model, and in the shallow part of the reservoir (i.e., meteoric watercontamination). A statistical multivariable analysis (Factor Analysis) wasaccomplished to better constrain the correlation between the paroxysmalphases of the seismic sequence and the observed trends and spike-likeanomalies. The groundwater variations was inferred to occur mainly insidethe ETB, from depth (1–2 km) up to surface, particularly in associationof the Sellano earthquake (14/10/1997) and of the seismic re-activationof the sequence at the end of March 1998 (Gualdo Tadino-Rigali andVerchiano areas). The lack of deeper input from below the ETB (slightsignature of PCB), as the lack of He mantle signature, during the seismicperiod as a whole, accounted for seismogenic fault segments rooted onlyin the crust. The results also provide useful information about theearthquake-related response mechanisms occurring at this site, thatrepresent the basic task for planning and managing the impendinghydro-geochemical network aimed at defining the relationships betweenseismic cycle, fluids and reliable earthquake forerunners.     

A performance‐based framework for adaptive seismic aftershock risk assessment

Operative seismic aftershock risk forecasting can be particularly useful for rapid decision‐making in the presence of an ongoing sequence. In such a context, limit state first‐excursion probabilities (risk) for the forecasting interval (a day) can represent the potential for progressive state of damage in a structure. This work lays out a performance‐based framework for adaptive aftershock risk assessment in the immediate post‐mainshock environment. A time‐dependent structural performance variable is adopted in order to measure the cumulative damage in a structure. A set of event‐dependent fragility curves as a function of the first‐mode spectral acceleration for a prescribed limit state is calculated by employing back‐to‐back nonlinear dynamic analyses. An epidemic‐type aftershock sequence model is employed for estimating the spatio‐temporal evolution of aftershocks. The event‐dependent fragility curves for a given limit state are then integrated together with the probability distribution of aftershock spectral acceleration based on the epidemic‐type aftershock sequence aftershock hazard. The daily probability of limit state first‐excursion is finally calculated as a weighted combination of the sequence of limit state probabilities conditioned on the number of aftershocks. As a numerical example, daily aftershock risk is calculated for the L'Aquila 2009 aftershock sequence (central Italy). A representative three‐story reinforced concrete frame with infill panels, which has cyclic strength and stiffness degradation, is used in order to evaluate the progressive damage. It is observed that the proposed framework leads to a sound forecasting of limit state first‐excursion in the structure for two limit states of significant damage and near collapse. Copyright © 2014 John Wiley & Sons, Ltd.     

Evidence of weathering stages of phyllosilicates from biotite/muscovite to kaolinite, probed by EPR spectroscopy

We report on a paramagnetic anisotropy study of three layered phyllosilicates. The mineral samples were characterized through X-ray powder diffraction (XRPD), X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). Based on EPR measurements of samples oriented parallel or perpendicular to the magnetic field lines, we show how the substitutional iron is transformed from Fe(II) (biotite) into Fe(III) (muscovite and kaolinite) species and from axial Fe(III) coordination sites (muscovite) to rhombic (kaolinite) sites in response to weathering.     

Evaluation of seismic performance of pile‐supported models in liquefiable soils

The seismic performance of four pile‐supported models is studied for two conditions: (i) transient to full liquefaction condition, i.e. the phase when excess pore pressure gradually increases during the shaking; (ii) full liquefaction condition, i.e. defined as the state where the seismically induced excess pore pressure equalises to the overburden stress. The paper describes two complementary analyses consisting of an experimental investigation, carried out at normal gravity on a shaking table, and a simplified numerical analysis, whereby the soil–structure interaction (SSI) is modelled through non‐linear Winkler springs (commonly known as p–y curves). The effects of liquefaction on the SSI are taken into account by reducing strength and stiffness of the non‐liquefied p–y curves by a factor widely known as p‐multiplier and by using a new set of p–y curves. The seismic performance of each of the four models is evaluated by considering two different criteria: (i) strength criterion expressed in terms of bending moment envelopes along the piles; (ii) damage criterion expressed in terms of maximum global displacement. Comparison between experimental results and numerical predictions shows that the proposed p–y curves have the advantage of better predicting the redistribution of bending moments at deeper elevations as the soil liquefies. Furthermore, the proposed method predicts with reasonable accuracy the displacement demand exhibited by the models at the full liquefaction condition. However, disparities between computed and experimental maximum bending moments (in both transient and full liquefaction conditions) and displacement demands (during transient to liquefaction condition) highlight the need for further studies. Copyright © 2016 The Authors Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.     

Calibration of rainfall-runoff models in ungauged basins: A regional maximum likelihood approach

Parameter estimation for rainfall-runoff models in ungauged basins is a challenging task that is receiving significant attention by the scientific community. In fact, many practical applications suffer from problems induced by data scarcity, given that hydrological observations are often sparse or unavailable. This study focuses on regional calibration for a generic rainfall-runoff model. The maximum likelihood function in the spectral domain proposed by Whittle [40] is approximated in the time domain by maximising the fit of selected statistics of the river flow process, with the aim to propose a calibration procedure that can be applied at regional scale. Accordingly, the statistics above are related to the dominant climate and catchment characteristics, through regional regression relationships. The proposed technique is applied to the case study of 4 catchments located in central Italy, which are treated as ungauged and are located in a region where detailed hydrological, as well as geomorphologic and climatic information, is available. The results obtained with the regional calibration are compared with those provided by a classical least squares calibration in the time domain. The outcomes of the analysis confirm the potential of the proposed methodology and show that regional information can be very effective for setting up hydrological models.