1,720,960 research outputs found
Engineering geological properties of the Phlegrean pozzolan soil and effect of the suction on the stability of cut slopes
No full textPozzolan is an incoherent to a pseudo-coherent pyroclastic soil that is much diffused in the Phlegrean Fields and has been used since ancient times for cement making. The industrial and economic relevance of this geological material gives rise to quarrying activities distributed in the Phlegrean area, which are carried out by means of pit quarries. These issues stimulated engineering geological analyses, in order to comprehend the conditions of stability of the quarry cut slopes discussed in this paper. Pozzolan soil, due to its prevailing sandy and silty components, among the other typical features of pyroclastic soils, does not have a negligible apparent cohesion in unsaturated conditions. These engineering geological issues motivated the interest in the stability analyses of cut slopes in pozzolan soil, also considering the effect due to the variable water content related to hydrologic regime. This paper regards the results of engineering geological analyses carried out on a sample area that corresponds to a cut slope of a pozzolan pit quarry located in Giuliano in Campania (NA), in the Zaccaria-Settecainati locality where the pozzolan outcrops in this area with its typical features. In order to evaluate the influence of the hydrologic regime on the mechanical characteristics of pyroclastic soils, and therefore on the stability of the artificial slopes, different engineering geological analyses have been applied, integrated with those techniques typical of the unsaturated soil hydraulic characterisation. In this paper, the results of field and laboratory experimental analyses carried out on the pozzolan soil including soil identification and the engineering geological classification, the estimation of mechanical and water retention properties are discussed. The application of the unsaturated shear strength model has allowed the estimation of the apparent cohesion effect. From these results, verified by means of direct shear tests in unsaturated conditions, the role of mechanical properties and the suction effect on the cut slope critical height, and therefore on the slope stability, have been comprehended
Engineering geological models of the initial landslides occurred on April 30 2006, at Mount di Vezzi (Ischia Island, Italy)
No full textOn the April 30th, 2006, during the early morning, five shallow landslides were triggered on the northern side of the Mount di Vezzi (Ischia Island, Italy) that moved down slope, as very rapid flows, channelled into the hydrographical network, and reached the foot of the relief. One of the landslides stroke and destroyed a building located in correspondence of the outlet of a channel, leading to the loss of four human lives. Already by the earliest surveys, the landslides were recognised as shallow and involving loose pyroclastic soils covering a volcanic bedrock just for a depth less than one meter. Moreover the landslides appeared to be classifiable with a complex style and, according to the grain size of the depleted soils, as debris slides - debris flows with an intermediate phase of debris-avalanches. These general features make the landslides of Mount di Vezzi very similar to those that typically occur in the peri-vesuvian area on a carbonate bedrock. Owing to both these similarities, despite the different bedrock, and the interest in understanding the triggering mechanism leading to the initial debris slide, the research has been focused in the reconstruction of engineering geological models of the initiation areas. With this specific purpose, field surveys consisted of topographic, stratigraphic, penetrometric measurements as well as hydraulic testing have been carried out. Laboratory tests on the pyroclastic soils have been also executed in order to characterise their physical and index properties. Among the principal results achieved are the reconnaissance of a rotational kinematics of the initial slides and of the involvement of the surficial pyroclastic deposits, very loose and permeable, overlapping a fine ash pyroclastic soil with higher compaction grade and lower permeability. The field analyses, extended up to the characterisation of the discontinuities network in the outcrops of the volcanic bedrock located above the landslides, confirmed the hypothesis that the local increase of pore pressure up to the saturation due to a high intensity/duration rainfall as being the triggering factor. As for the landslide susceptibility assessment, the spatial localisation of the initial debris slides can be referred to a critical combination of higher pyroclastic soil thickness and slope angle, favoured by local morphological conditions and by irregularities of the interface with the bedrock. Basing on these characters, besides of the similarity in hydrogeomorphological conditions, the landslides occurred on the Monte di Vezzi can be considered analogous to those of the numerous other cases occurred along the peri-vesuvian carbonate slopes
Analysis of Shear Strength Variability of Ash-Fall Pyroclastic Soils Involved in Flow-Like Landslides
No full textRainfall-induced shallow landslides of flow-like type are very common in ash-fall pyroclastic soils originated from explosive activity of the Somma-Vesuvius volcano (southern Italy). Over the last few centuries, these phenomena have frequently affected pyroclastic soil-mantled slopes of mountain ranges that surround the volcano causing hundreds of casualties. Many researches have been focused on this topic, especially after the occurrence of the deadly debris flow events of May 1998, which hit Sarno Mountains causing 160 victims. Among the various aspects studied, aimed at the assessment and mapping of hazard to landslide initiation and propagation, the estimation of shear strength of ash-fall pyroclastic soils still deserves to be advanced. This is especially due to the relevant spatial variability of geotechnical properties which are controlled by complex stratigraphic settings. According to such a research focus, the present paper deals with physical and shear strength laboratory characterizations of ash-fall pyroclastic soils and the estimation of the inherent variability. A total number of 97 direct shear tests, supported by grain size and Atterberg’s limits analyses, were carried out. The high number of tests allowed to perform a statistical analysis based on quantile regression approach and aimed at considering the uncertainty related to the high variability of Mohr–Coulomb’s shear strength parameters. The results obtained show values, especially for the drained friction angle (φ′), generally higher than those considered in literature. Outcomes of the study and the approach proposed can be conceived as a benchmark for further analyses aimed at the assessment of hazard to initiation of this type of landslides or related physically-based rainfall thresholds
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Analysis of Shear Strength Variability of Ash-Fall Pyroclastic Soils Involved in Flow-Like Landslides
Full text linkVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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