1,720,957 research outputs found
Comprehensive database of land subsidence in 143 major coastal cities around the world: overview of issues, causes, and future challenges
Full text linkSubsidence refers to the gradual lowering or sudden sinking of the ground surface and is known to impact human lives in terms of damages to the infrastructures, utility lines, and buildings as well as changes in the surficial drainage systems and groundwater conditions. The impacts of land subsidence will be greater in the future, considering the sea level rise, population growth, intensification of coastal erosion and extreme events, as well as increase in flood risk or freshwater salinization, mostly in coastal cities. The main aim of this work is to provide an open-source, peer-reviewed, and comprehensive database identifying the main and secondary causes of land subsidence in 143 coastal cities. We highlight the potential impacts of subsidence that are still unknown in some at-risk cities and non-existence of mitigation measures. The database additionally shows that mitigation measures, specifically those addressing subsidence due to groundwater extraction, have proven successful in the past. The proposed database aims to increase the knowledge on the subsidence phenomenon and also global awareness of land subsidence issues among researchers, the scientific community, stakeholders, and policymakers in terms of urban planning and development
The Quay Walls of Amsterdam, Netherlands: An Approach for Collapse Risk Mitigation at the Municipal Scale Based on Multisource Monitoring and Surveying Data
No full textThe City of Amsterdam is responsible for the maintenance of 600 km of historic quay walls, most of which are over 100 years old while others are 300 years old and are experiencing stability and degradation problems. A lack of knowledge about the as-built information and the current conditions of the retaining structures and their foundation systems exists, and very limited guidelines for the assessment of quay walls are available. Predicting the time when the quay walls are no longer safe is a key challenge in their end-of-life assessment. For this purpose, monitoring of the quay walls via conventional techniques (e.g., in situ surveys, topographic levelling and tachymetry) combined with satellite Multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) data provides updated information on the displacements affecting the retaining structures and/or their foundations. This paper develops a multiscale methodology, consisting of three phases, that allow (1) the prioritization of the most exposed retaining structures (quay walls) at the municipal scale, (2) the retrieval of empirical relationships between different damage/movement indicators and quantitative displacement descriptors obtained via in situ surveys and terrestrial monitoring data, and (3) the identification of the most probable collapse mechanism by jointly analyzing the wall crack patterns and monitoring data. The results show that this approach could play a fundamental role to set up sustainable risk mitigation strategies at the municipal scale
Empirical fragility curves for settlement-affected buildings: Analysis of different intensity parameters for seven hundred masonry buildings in The Netherlands
Full text linkThe analysis and prediction of damage to buildings resting on highly compressible fine-grained ‘‘soft soils” containing (organic) clay
and peat are key issues to be addressed for a proper management of subsidence-affected urban areas. Among the probabilistic approaches suggested in literature, those oriented to the generation of empirical fragility curves are particularly promising provided that a comprehensive dataset for both the subsidence-related intensity (SRI) parameters and the corresponding damage severity to buildings is available. Following this line of thought, in the present paper, a rich sample of more than seven hundred monitored (by remote sensing) and surveyed masonry buildings – mainly resting with their (shallow or piled) foundations on soft soils – is analysed in four urban areas of The Netherlands. Probabilistic functions in the form of fragility curves for building damage are retrieved for three different SRI parameters (i.e., differential settlement, rotation and deflection ratio) derived from the processing of Synthetic Aperture Radar (SAR) images by way of a differential interferometric (DInSAR) technique in combination with the severity levels of the damage recorded from the visual inspection of over 700 masonry buildings. As a novelty with respect to earlier similar studies, the work points out the methodological steps to be followed in order to identify the most appropriate SRI parameter among the selected ones. Thus, the objective of the paper is to improve the existing geotechnical forecasting tools for subsidence-affected urban areas, in order to target areas that require more detailed investigations/analyses and/or to select/prioritize foundation repairing/replacing measures
Multi-source monitoring data and numerical analyses for the assessment of settlements affecting built-up areas in variable soil conditions
No full textThis paper presents an integrated analysis based on the use of multi-source wide-area datasets consisting of hydro-mechanical properties of geomaterials, in-situ investigations/measurements (e.g. groundwater levels in wells) and innovative space-borne data (i.e. DInSAR techniques) to support numerical analyses aimed at assessing and predicting the settlements affecting built-up areas in variable soil conditions. To this aim, an expeditious procedure was developed and tested with reference to a district in Rotterdam City (The Netherlands) affected by subsidence phenomena due to the presence of heterogeneous settling strata mainly composed by peat and organic soils. The results obtained allowed investigating the role of predisposing factors of the settlement occurrence and assessing the induced damage on buildings. Considering the widespread diffusion of such geohazards, the followed procedure could help the in-charge authorities to carry out activities at urban scale aimed at identifying the areas most affected by subsidence risk and to select the most suitable and sustainable mitigation strategies.Applied MechanicsGeo-engineerin
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
Pile foundations in the Netherlands: an analysis of the 4D/8D method through numerical modelling
No full textTheNetherlands is a densely populated country and is located in an areawhere the shallowsubsurfacemainly consists ofHolocene and Pleistocene soils. To build permanent structures, enough bearing capacity is needed to provide sufficient support for these structures. However, Holocene (soft) soils typically do not provide sufficient support. In the western part of the country, the soft soils from the Holocene overlay the stiffer Pleistocene soils. To still be able to construct at locations where soft soils are found, pile foundations are needed to transfer the loads through the soft soil onto the stiff soil in order to provide for sufficient bearing capacity. The normativemethod for determining pile bearing capacity in the Netherlands uses a relatively straightforward semi-empirical approach known as the 4D/8D or the Dutch method. This method was based on the work of [vanMierlo and Koppejan, 1952] who introduce the logarithmic spiral theory. Apart from small modifications and elaborations, the method has been used ever since. To get to a reasoned solution on how to calculate and design pile foundations the Eurocode [Normcommissie 351 006 ’Geotechniek’, 2017a] was introduced. One of the (original) aims of the Eurocode was to harmonise rules and regulations regarding, amongst others, pile foundations. To prepare this harmonisation, Belgium, France and the Netherlands took a closer look into their calculation methods. For the Netherlands this research was performed by a committee who presented their findings in CUR 229 - “Axiaal belaste palen” [CUR B&I, 2010]. From CUR 229 it was found the pile tip capacity was overestimated. In other words, the calculated pile tip capacity was higher than the measured pile tip capacity. This overestimation led to a reduction of ®p of 30% starting on the 1st of January 2017. (®p is the factor which reduces the pile tip resistance for different pile types, see Appendix A.) A point of interest is the overestimation of the pile tip capacity, which seems to become more prominent when the pile goes deeper into a non-cohesive soil. It was even found, a lower ®p is not required for piles installed less than 8D into the bearing layer. The reduction of ®p seems to contradict with practice, because no cases of damage are known regarding the bearing capacity of pile foundations. Several explanations for this might be valid. For example, hidden safeties may prevent overall safety issues to arise. In addition, errors may occur in the determination of the pile capacity from pile load tests or in the Dutch method for calculating pile tip capacity. This leads to the two main subjects for this thesis. On the one hand, the hidden mechanism of residual loads is considered and on the other hand, the zone of influence at the pile tip during failure is analysed. To analyse the above-named subjects, the 4D/8D method was put under scrutiny. First, it was compared to other (international) analytical methods, which determine the bearing capacity directly from CPT data. Furthermore, the zone of influence around the pile tip is considered inmore detail by analysing the analytical approach and comparing this to the results of numerical models. This led to the conclusion that the observed overestimation can partly be explained by the inaccuracy of the assumed zone of influence around the pile tip, especially regarding the extent of this zone above the pile tip (8D). As this extent is too large, the 4D/8D method results in a too low average cone resistance in the 8D zone (for piles installed less than 8D into the bearing soil layer). In combination with the ‘old’ ®p , this leads to a reasonably accurate estimation of the pile tip capacity compared to the measured tip capacity. However, the observed extent of the zone of influence above the pile tip, in the FEMmodels, is in the order of 1 to 1.5D. The average cone resistance in this zone will in most cases be higher than in a zone extending 8D above the pile tip. The hidden mechanism of residual loads is implemented in a numerical model, with the use of a static load on top of the pile. The residual loads are caused by the installation of the pile and so, they are considered to be installation effects. No analytical or numerical models or procedures were found in literature to quantify the xiii xiv 0. Abstract residual load. Residual loads were implemented using a procedure defined in this thesis, taking into account the maximum pile tip capacity as indicator for the order of magnitude for the residual load. This is done, because a drawback of FEM models is; they are not able to calculate large strains, which occur during installation of a pile. Therefore the installations effects (like residual loads) have to be implemented indirectly. The horizontal compression due to installation is modelled as an installation effect according to the procedure of [Broere and van Tol, 2006]. Both installation effects are validated using data from CUR 229 and they are subjected to a sensitivity analysis. Furthermore, the softening or peak behaviour of soils might have a significant influence on the zone of influence around the pile and on the residual loads, as for both cases, the soil is loaded up to failure. Most regular constitutive models do not take into account this behaviour. Due to the fact the Hypo Plasticity (HP) model takes into account this peak behaviour, it was used to performthe FEM analysis. During the final stages of this thesis, scaled pile load tests were performed. The results of these tests were analysed to find the presence and order of magnitude of the residual load in a pile. However, as the test results were incomplete, only first assumptions were made that indicated the presence of residual loads. No substantiated conclusion could be drawn regarding the magnitude. Due to the observed importance of residual loads in this thesis, the residual loads should be measured during load tests more extensively using Osterberg cells or fibre optics. The installation effects are modelled in the Hypo Plasticity model with reasonable confidence, but future research is needed on models that can model the installation process (for example theMaterial PointMethod). Furthermore, the small strain parameters of the HP model should be taken into account. This thesis questions the 4D/8D method and shows some of its inaccuracies. However, more extensive research should be done considering the extent of the zone of influence and the limiting value defined by in the Dutchmethod. Also, the interaction between the shaft and the pile tip resistance has to be evaluated, as this thesis indicates they interfere with each other if the Dutch method is considered. Besides the zone of influence and the residual loads, the failure criterion stated by NEN 9997-1 is questioned. Failure of a pile happens when the pile tip has moved 10%D [Normcommissie 351 006 ’Geotechniek’, 2017a], but the FEM models show more displacements at failure, where failure is defined by themoment the models cannot stabilise anymore and therefore fail to calculate for a certain load step.Geo-Engineerin
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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