Prediction of time to slope failure: a general framework

The prediction of time to slope failure (TSF) is a goal of major importance for both landslide researchers and practitioners. A reasonably accurate prediction of TSF allows human losses to be avoided, damages to property to be reduced and adequate countermeasures to be designed. A pure “phenomenological” approach based on the observation and interpretation of the monitored data is generally employed in TSF prediction. Such an approach infers TSF mainly from the ground surface displacements using regression techniques based on empirical functions. These functions neglect the rheological soil parameters in order to reduce the prediction uncertainties. This paper presents an overlook of the methods associated with this approach and proposes a unique expression encompassing most of the previously proposed equations for TSF prediction, thus offering a general framework useful for comparisons between different methods. The methods discussed in this paper provide an effective tool, and sometimes the only tool, for TSF prediction. The fundamental problem is always one of data quality. A full confidence in all assumptions and parameters used in the prediction model is rarely, if ever, achieved. Therefore, TSF prediction models should be applied with care and the results interpreted with caution. Documented case studies represent the most useful source of information to calibrate the TSF prediction models.     

Numerical modeling and mechanical analysis of an innovative soil anchoring system

In this paper, the pull-out performance of an innovative system for soil anchoring is mechanically interpreted on the basis of a preliminary finite element investigation. The system consists of a tie rod equipped with thick steel sockets, extruding into the soil to increase the overall pull-out bearing capacity. The effectiveness of the anchorage is shown to be mainly due to the steel sockets, producing two correlated strength mechanisms: a direct one, associated with the shear/flexural strength of the sockets themselves; and an indirect one, in the form of a remarkable increase in the normal confinement on the tie rod and hence in the mobilizable shear stresses. The numerical results are finally exploited to conceive a simplified mechanical model for the interpretation/prediction of the pull-out anchor performance.     

Magnetite biomineralization induced by Shewanella oneidensis

Shewanella oneidensis is a dissimilatory iron reducing bacterium capable of inducing the extracellular precipitation of magnetite. This precipitation requires a combination of passive and active mechanisms. Precipitation occurs as a consequence of active production of Fe²⁺_(aq) when bacteria utilize ferrihydrite as a terminal electron acceptor, and the pH rise probably due to the bacterial metabolism of amino acids. As for passive mechanisms, the localized concentration of Fe²⁺_(aq) and Fe³⁺_(aq) at the net negatively charged cell wall, cell structures and/or cell debris induces a local rise of supersaturation of the system with respect to magnetite, triggering the precipitation of such a phase.These biologically induced magnetites are morphologically identical to those formed inorganically in free-drift experiments (closed system; 25 °C, 1 atm total pressure), both from aqueous solutions containing Fe(ClO₄)₂, FeCl₃, NaHCO₃, NaCO₃ and NaOH, and also from sterile culture medium added with FeCl₂. However, organic material becomes incorporated in substantial amounts into the crystal structure of S. oneidensis-induced magnetites, modifying such a structure compared to that of inorganic magnetites. This structural change and the presence of organic matter are detected by Raman and FT-IR spectroscopic analyses and may be used as a biomarker to recognize the biogenic origin of natural magnetites.     

Interaction between ultrapotassic magmas and carbonate rocks: Evidence from geochemical and isotopic (Sr, Nd, O) compositions of granular lithic clasts from the Alban Hills Volcano, Central Italy

Magma-carbonate rock interaction is investigated through a geochemical and Sr-Nd-O isotope study of granular lithic clasts (ejecta) from the Alban Hills ultrapotassic volcano, Central Italy. Some samples (Group-1) basically represent intrusive equivalents of Alban Hills magmas. A few samples (Group-2) are ultramafic, have high MgO (∼30 to 40 wt%) and δ¹⁸O‰, and originated by accumulation of mafic phases that crystallised from ultrapotassic melts during assimilation of dolomitic rocks. Group-3 ejecta consist of dominant K-feldspar, and show major element compositions similar to phonolites, which, however, are absent among the Alban Hills volcanics. Finally, another group (Group-4) contains corroded K-feldspars, surrounded by a microgranular to porphyritic matrix, made of igneous minerals (K-feldspar, foids, clinopyroxene, phlogopite) plus wollastonite, garnet, and some cuspidine. Group-4 ejecta are depleted in SiO₂ and enriched in CaO with respect to Group-3.The analysed ejecta have similar ¹⁴³Nd/¹⁴⁴Nd (0.51204-0.51217) as the Alban Hills lavas, whereas ⁸⁷Sr/⁸⁶Sr (0.70900-0.71067) is similar to lower. Whole rocks δ¹⁸O‰ ranges from +7.0 to +13.2, reaching maximum values in ultramafic samples. A positive correlation with CaO is observed in single rock groups. Large Ion Lithophile Element (LILE) abundances and REE fractionation are generally high, and extreme values of Th, U and LREE are found in some Group-3 and Group-4 rocks.Mineralogical, petrological and geochemical data reveal extensive interaction between magma and carbonate wall rocks, involving both dolostones and limestones. These processes had dramatic effects on magma compositions, especially on phonolites, which were transformed to foidites. Evidence of such a process is found in Group-4 samples, in which K-feldspar is observed to react with a matrix that represents strongly undersaturated melts formed by interaction between silicate magma and carbonates. Trace element data also testify to a very important role for F-CO₂-H₂O-S fluids during magma-wall rock interaction. Fluid transfer was responsible for extreme enrichments in Th, U, and LREE especially observed in Group-3 and Group-4 rocks. Implications of these processes for potassic magma evolution in Central Italy are discussed.     

Geological characterization of the Prestige sinking area

The tanker Prestige sank off NW Iberia on the 19th November 2002. The stern and bow of the Prestige wreck are located on the southwestern edge of the Galicia Bank, at 3565 m and 3830 m water depths, respectively. This bank is a structural high controlled by major faults with predominant N-S, NNE-SSW, and NNW-SEE trends. It is characterized by moderate to low seismic activity. The faults have controlled the local depositional architecture, deforming, fracturing, relocating and distributing sediments since the Valangian (early Cretaceous). The Prestige sinking area corresponds to an asymmetric half-graben structure with a N-S trend, which conditions the present-day morphology. The faulted flank outcrops and its activity and erosion have favoured the occurrence of mass-movements (slumps, slump debris, mass-flows and turbidity currents), building valleys and depositional lobes. Nearsurface sediments comprise mostly terrigenous and biogenous turbiditic muds and sands with a minor presence of hemipelagic muds, except on the fault scarp where pelagites predominate. Potential geological hazards resulting from tectonic and sedimentary processes affect almost the entire Prestige sinking area.     

Total and labile metals in surface sediments of the tropical river-estuary system of Marabasco (Pacific coast of Mexico): Influence of an iron mine

Marabasco is a tropical river-estuary system comprising the Marabasco river and the Barra de Navidad Lagoon. The river is impacted by the Pe?a Colorada iron mine, which produces 3.5 million tons of pellets per year. Thirteen surface sediment samples were collected in May 2005 (dry season) in order to establish background levels of Al, Cd, Co, Cu, Fe, Ni, Pb, and Zn in the system and to ascertain the potential mobility of metals in the sediments. Analyses were carried out in the fraction finer than 63 microm, and labile metals extracted according the BCR procedure. Certified reference materials were used for validation of methods. Total concentrations of Cd, Co, Cu, Ni, Pb, and Zn were in the range of 0.05-0.34, 6-95, 0.7-31, 9-26, 2-18, and 53-179 mgkg(-1), respectively; Al and Fe ranges of 24-127, and 26-69 mgg(-1) correspondingly. Cadmium was found to be significantly labile in the sediments (20-100%), followed by Co (0-35%), Ni (3-16%) and Zn (0-25%), whereas the labile fraction for Cu, Fe and Pb was almost negligible (<4%). According with the total metal concentrations, background levels and normalised enrichment factors (NEF) of the metals studied, the impact of the Pe?a Colorada iron mine on the Marabasco system is lower than expected when compared with other similar World systems influenced by mining activities.     

A multidisciplinary approach to reveal the Sicily Climate and Environment over the last 20 000 years

We present a thorough review of the knowledge on the climate and environment in Sicily over the last 20 000 years, taking into account results of several studies carried using terrestrial and marine records. We obtain a coherent framework of the most important changes succeeded in the island, even if some points need further investigation. All the reconstructions of surface temperatures of the seas and the air surrounding Sicily point out severe climatic conditions during the last glacial period. The steppe- and semisteppe-like vegetation pattern testifies, together with additional evidence from geochemical data of lacustrine evidence, markedly arid conditions. Fi-nally, significant episodes of sea level drop connected Sicily to the Italian Peninsula and favoured the dispersion of faunal elements from southern Italy. The transition between the last glacial and the Holocene was not characterized by a gradual warming but was punctuated by two abrupt suborbital climatic fluctuations: Bølling-Allerød (warm) and Younger Dryas (cold), as recognized in the sediments recovered close to the northern and southern coast of Sicily. A denser arboreal cover is possibly indicated by the occurrence of dormouse and Arvicola remains. Finally the sensitivity of Sicily to climate perturbations is demonstrated by the occurrence of repeated subtle climatic anomalies during the Holocene, including the Little Ice Age, also known from historical chronicles. Forests, woods and Mediterranean maquis developed in the early-middle Holocene. Thereafter was a general decline of arboreal vegetation, following a general aridification trend that seems to be a common feature in southern Europe and North Africa. Science Greek colonization (7^th century before Christ), the landscape was intensively modelled for agriculture and breeding, leading to a significant loss of vegetation cover.