1,721,198 research outputs found
Numerical simulation of the groundwater flow leading to sand boil reactivation in the Po River
No full textThe reliability of river embankments is essential for flood risk management. The Po River, which flows through the North of Italy, is safeguarded over half of its length by major river embankments. Performance assessment of such water-retaining structures has become a major concern following some significant flood events in the past. Among the possible initiating causes of failure, backward erosion piping turns out to be particularly threating in the middle-lower stretch of the river. In particular, the November 2014 high-water event triggered the formation or reactivation of a few important sand boils. The paper presents a preliminary 3D finite element model of the groundwater flow through a selected cross section of the Po river, located in the Province of Reggio Emilia, which experienced a reactivation of piping phenomena after the 2014 event. The numerical model, based on a detailed geotechnical characterization obtained from in situ tests, was calibrated on the basis of the 2014 high-water event measurements and verified for a subsequent event that took place in November 2016, though without any relevant sand boil reactivation. Results are discussed with the aim of providing some insight into the mechanism under study
Correction Factor on Dynamic Force in a Marsh Funnel Test for Tunneling
No full textThis paper presents an improvement on a previous model for predicting the Marsh funnel (MF) test that is used in slurry shield tunneling for evaluating the rheological properties of bentonite slurries. The improvement focuses on the prediction of the dynamic part for fluids with small MF times. The velocity profile of the Herschel-Bulkley fluid in a laminar pipe flow condition is first investigated and a correction factor is introduced in the improved model. Comparisons of results from experiments and calculations with the previous model confirm the improved performance over the existing model. The rheological parameters obtained from the improved model show good resemblance to those obtained from a laboratory viscometer. The work also provides a reference to similar applications such as fluid transportation through pipelines where dynamic pressure dominates and therefore should be correctly predicted considering its velocity profile in a laminar condition.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Offshore and Dredging Engineerin
Geosynthetic-reinforced soil retaining walls subjected to surcharge loads
No full textCurrently there are many solutions to improve soil properties. Geosynthetic materials (geogrids and geotextiles) are particularly useful in reinforced soil systems. Geosynthetic-reinforced structures have been widely used in road engineering and in the construction of railways due to their economy and effectiveness compared to the traditional soil improvement methods. A considerable number of retaining structures have been successfully constructed using geosynthetic reinforcement layers. In many of these retaining structures, footings are located on the backfill and over the soil (e.g. footings on bridge abutments or roads located on top of the retaining structure).
Despite the increasing use of geosynthetic-reinforced soil systems for retaining structures, still uncertainty exists concerning the real interaction of these materials with the soil and consequently, the current design methods need validation for different conditions and interactions. The soil-geosynthetic interaction can be very complex because it is affected by structural, geometrical, and mechanical characteristics of the geosynthetic, by the mechanical properties of the soil and by boundaries and loading conditions.
This thesis starts with exploring the existing literatures on the soil-geosynthetic interactions in MSE walls. The review of the literatures underpins further development in the soil-geosynthetic interaction by experimental, analytical and numerical modelling for the mechanically stabilized earth wall systems and under the strip footing load. In mechanically stabilized earth walls and especially under the strip footing load, the necessary reinforcement length and consequently the size of the reinforced block depend on the reinforcement layers stiffness and strength, soil properties and interface apparent coefficient of friction.
Next, model test results obtained from full-scale tests on the geogrid reinforced stabilized earth walls were analysed with analytical methods. The model MSE walls were prepared and tested at Brandenburg University of Technology Cottbus-Senftenberg (Pachomov et al., 2007) and the data were provided by the Naue Company. Two models were constructed, one with a full-height plywood panel (flexible) and another one with a full-height concrete face (rigid). There were two different steps considered in the full-scale models; the backfill construction step with a preloading effect caused by vibratory plate compactors for each layer of sand between the geogrid layers and the static strip footing load after the preloading effect from a localized roller compactor load. The instrumentation used in these tests provided valuable measurements of strains on the reinforcements, lateral wall deflection, vertical and lateral earth pressures before and after applying the strip footing load. These measurements have been used as a database for the evaluation of analytical and numerical methods commonly used in design of mechanically stabilized earth walls with different facing panels (rigid and flexible) and considering the preloading effect.
Comparison between the measured maximum reinforcement tensile forces calculated from the strain gauges results after the backfill construction step with the AASHTO (2012) and K-stiffness methods showed that, the AASHTO (2012) method overestimated the maximum tensile force specially for the deeper layers and the K-stiffness and simplified stiffness methods underestimated the maximum tensile forces for the full-scale tests specially in upper layers. By increasing the overall flexural rigidity of the facing panel, the lateral wall deflection and reinforcement strains decrease in both the analytical models as in the measurements. A new modified analytical method has been developed based on the existing methods by considering the facing panel rigidity and compaction load (preloading) effects for calculating the maximum tensile forces in reinforcement layers and maximum wall deflections. This new model leads to a better agreement with the measurements.
A scaled experimental setup (compared to the full-scale tests) was made to investigate the real interaction of the soil-reinforcement layers more in detail. Different types of geosynthetic materials were tested under different loading conditions. These scaled experimental tests had the scale factor of 1/5 compared to full-scale tests for both the size of model and the reinforcement stiffness. There were two loading steps in small-scale models similar to full-scale models, the first loading step (to consider the effect of preloading from a roller compactor in full-scale models) and the second loading step (to consider the effect of strip footing load in full-scale models). From the PIV (Particle Image Velocimetry) analysis it was found that two failure lines with the angle of (π/4+φ/2) formed under the strip footing load: one from inner edge of the strip footing to the wall face (shallow position) and another from the outer edge of the strip footing (deep position). The facing panel rigidity and preloading influences the lateral wall deflection and vertical earth pressure and consequently, the maximum tensile load in the reinforcement. PIV analysis showed that the stiffness of the nonwoven geotextile in-soil is different from the in-air condition
After that, the full-scale measurements are compared with the results of the 2D numerical analysis for the vertical and horizontal earth pressures, maximum tensile forces in reinforcement layers after backfill construction step and after considering different methods for compaction load. The numerical results illustrate that for the rigid face compared to the flexible face, the upper layers have more influence on the stability and the wall deflection under the strip footing load. By considering two equal distributed loads (as the compaction load) in top and bottom of each soil layer, there is good agreement between the full-scale tests and numerical modelling in the backfill construction step. The numerical models showed the equivalent static load can be used for the preloading effect of the roller compactor to have the same tensile loads and maximum wall deflection under the static strip footing load.
2D numerical calculations were used to investigate the influence of a horizontal restriction of the strip footing load. When only vertical movement is allowed, the maximum wall deflection is lower than when horizontal movement is allowed.
Finally, 2D numerical analysis was performed to simulate the small-scale tests by considering the facing panel rigidity and preloading effects. There is good agreement between the 2D numerical analysis and small-scale test results except for the non-woven geotextile. Considering the higher stiffness for the non-woven geotextile under confining pressure, there is still difference between the numerical and test results
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Infiltration and excess pore water pressures in front of a TBM : experiments, mechanisms and computational models
Get PDFVariations on the Author
Get PDF“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
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