1,720,971 research outputs found
Challenges in the characterisation of intact rock bridges in rock slopes
No full textIntact rock bridges have been recognised as of critical importance in the stability of rock slopes but still remain a poorly understood and challenging engineering problem both in respect to their measurement and their incorporation into design analyses. The objective of this paper is not to provide conclusive answers as to the definition and measurement of rock bridges, and the manner that they can be accounted for in rock slope stability analysis. Rather, we highlight important and as yet unanswered questions to allow review of fundamental rock bridge concepts and then proceed to provide new insight into how rock bridges may be incorporated into slope stability analysis. Early definitions of what constitute a rock bridge are somewhat limited, and the authors suggest that they could be improved by including important constraints such as “block forming potential” and “block kinematics”. In this context, this paper introduces an improved terminology (RBij) commonly used by the discrete fracture network (DFN) community to define rock bridge intensity relative to the sampling region. In rock engineering, the measurement of rock bridges is exacerbated by the fact that rock bridges are not visible unless the rock mass is exposed by human activities or by natural events such as rockfalls. This constitutes a major problem for engineering design scenarios, since it would not be possible to validate any assumption made with respect to extent of rock bridges without performing some form of field testing or back-analysis. The results of a of the Finite-Discrete numerical analysis are presented to support our conclusions with respect to the limitations current methods used to characterise rock bridge strength. The role of scale effects, block theory, kinematics and what we term “negative rock bridges” in stability analysis is discussed
A preliminary investigation on the role of brittle fracture in the kinematics of the 2014 san Leo landslide
Full text linkThe stability of high rock slopes is largely controlled by the location and orientation of geological features, such as faults, folds, joints, and bedding planes, which can induce structurally controlled slope instability. Under certain conditions, slope kinematics may vary with time, as propagation of existing fractures due to brittle failure may allow development of fully persistent release surfaces. In this paper, the progressive accumulation of brittle damage that occurred prior to and during the 2014 San Leo landslide (northern Italy) is investigated using a synthetic rock mass (SRM) approach. Mapping of brittle fractures, rock bridge failures, and major structures is undertaken using terrestrial laser scanning, photogrammetry, and high-resolution photography. Numerical analyses are conducted to investigate the role of intact rock fracturing on the evolution of kinematic freedom using the two-dimensional Finite-discrete element method (FDEM) code Elfen, and the three-dimensional lattice-spring scheme code Slope Model. Numerical analyses show that the gradual erosion of clay-rich material below the base of the plateau drives the brittle propagation of fractures within the rock mass, until a fully persistent, subvertical rupture surface form, causing toppling of fault-bounded rock columns. This study clearly highlights the potential role of intact rock fracturing on the slope kinematics, and the interaction between intact rock strength, structural geology, and slope morphology
A New Approach to Characterise the Impact of Rock Bridges in Stability Analysis
Full text linkRock bridges have been the subject of considerable research since the 1970’s with a focus on developing methods to measure rock bridges and quantifying their role with respect to rock mass strength. In the literature, rock bridges are generally defined as a portion of intact rock separating discontinuity surfaces; however, whether a portion of intact rock resists failure and, therefore, represents a critical rock bridge depends on the failure mechanisms that may develop within the rock mass. The difficulty of defining what constitutes a rock bridge is associated with the challenge of measuring rock bridges in the field. This aspect is often ignored by engineers and practitioners, who fail to recognise that rock bridges could exist even within a rock mass characterised by fully continuous surfaces. Furthermore, field evidence of rock slope failure shows that rock bridges do not fail at the same time, and a simple definition of a rock bridge as the distance between existing discontinuities cannot account for progressive rock mass damage and changes in stresses within a rock mass. The authors suggest that the concept itself of rock bridges may be flawed, and more attention should be given to better understanding damage-related processes, including time-dependent damage in the context of engineered structures
A FEM-DEM numerical analysis to study the instability of the Passo della Morte slopes (Carnian Alps, Italy)
No full textThe natural formation of rock slopes can result in the initiation of complex failure processes, including the deformation and fracturing of intact rock and the displacement of large individual blocks. The presence of non-persistent discontinuities may also promote stress concentrations that would result in stress induced fractures leading to the formation of continuous failure surfaces, thus creating the condition of kinematic freedom for previously finite and tapered blocks that may result in slope failure. This type of mechanism cannot be analyzed using a limit equilibrium approach and requires models capable of considering rock mass plastic yield, simulation of shear/tensile fracturing and ability to consider kinematic processes. In this context, hybrid finite-discrete element methods (FDEM) provide an attractive option for modelling rock slope failure mechanisms. In this paper a FDEM approach was applied to study a rock face located near the Passo della Morte (Carnian Alps, Italy), on the left flank of Tagliamento River valley. The rock face is approximately 130 m wide and 250 m high (650 to 900 m a.s.l.). The study includes 2D numerical analysis of a critical section for which the potential failure mechanism would be controlled by a series of faults bounding a densely stratified rock mass crossed by very persistent sub-vertical joints. Overall, the rock mass is divided into a large number of blocks of variable size, that are isolated by a dense network of discontinuities and random fractures. The importance of damage in the rock slope mass has been recognized by several researchers using remote sensing methods
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
Variations 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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