Numerical evaluation of three non-coaxial kinematic models using the distinct element method for elliptical granular materials

This is the accepted version of the following article: [Jiang, M. J., Liu, J. D., and Arroyo, M. (2016) Numerical evaluation of three non-coaxial kinematic models using the distinct element method for elliptical granular materials. Int. J. Numer. Anal. Meth. Geomech., 40: 2468–2488. doi: 10.1002/nag.2540.], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nag.2540/fullThis paper presents a numerical evaluation of three non-coaxial kinematic models by performing Distinct Element Method (DEM) simple shear tests on specimens composed of elliptical particles with different aspect ratios of 1.4 and 1.7. The models evaluated are the double-shearing model, the double-sliding free-rotating model and the double slip and rotation rate model (DSR2 model). Two modes of monotonic and cyclic simple shear tests were simulated to evaluate the role played by the inherent anisotropy of the specimens. The main findings are supported by all the DEM simple shear tests, irrespective of particle shape, specimen density or shear mode. The evaluation demonstrates that the assumption in the double-shearing model is inconsistent with the DEM results and that the energy dissipation requirements in the double-sliding free-rotating model appear to be too restrictive to describe the kinematic flow of elliptical particle systems. In contrast, the predictions made by the DSR2 model agree reasonably well with the DEM data, which demonstrates that the DSR2 model can effectively predict the non-coaxial kinematic behavior of elliptical particle systems.Peer ReviewedPostprint (author's final draft

JOLer: Una aplicación Java de escritorio para simular el modelo de juicios de aprendizaje de Weaver y Kelemen.

To assess judgment of learning (JOL) accuracy in metamemory, researchers have to measure how much the metamemory judgments adjust to the participant's memory-test performance. Absolute accuracy or calibration is the average correspondence between JOL and memory performance. Metamemory relative accuracy or resolution is a measure of how sensitive a participant is to the differential recallability between two studied items. Unfortunately, factors altering both calibration and resolution very often change also the distribution of JOL on the available scale for judgment. The problem with these effects on JOL distribution is that they could yield an altered resolution estimation due to the way in which its usual estimate is computed. JOLer simulates the behavior of participants in a typical metamemory procedure. The application is offered as a tool for metamemory researchers: it affords the opportunity to check whether, maintaining calibration parameters but changing JOL distributions between conditions, a different (and somewhat spurious) resolution estimate would be obtained.Para calcular la precisión de los juicios de aprendizaje (JJAA) en metamemoria los investigadores tienen que estimar en qué medida los juicios de un participante se ajustan a su rendimiento en una prueba de memoria. La precisión absoluta o calibración es la correspondencia media entre JA y rendimiento en memoria. La precisión relativa de metamemoria o resolución nos dice el grado de sensibilidad de un participante respecto a un diferencial de recuperabilidad entre dos ítems estudiados. Por desgracia, los factores que alteran la calibración y la resolución con frecuencia cambian también la distribución de JJAA a lo largo de la escala de juicio. El problema de estos efectos sobre la distribución de JJAA es que pueden dar lugar a una estimación de resolución distorsionada debido al modo en que se calcula el estimador habitual. JOLer simula el comportamiento de unos participantes en un procedimiento típico de metamemoria. La aplicación se presenta como una herramienta para investigadores de la metamemoria: ofrece la oportunidad de comprobar si, manteniendo los parámetros de calibración pero cambiando la distribución de JJAA entre condiciones, se obtendría una resolución estimada distinta (y en cierto grado artificial)

Use of tire derived aggregate in tunnel cut-and-cover

A case-history is reported in which tire derived aggregate (TDA) was successfully applied to reduce the weight of fill upon a cut-and-cover railway tunnel. Subsequent 3D numerical analyses are used to explore the effect of different assumptions about the constitutive model of the TDA material. Alternative dispositions of TDA around the tunnel section are also examined. Reductions of up to 60% in lining bending moment may be achieved. For the case analyzed the elastic description of the TDA has little influence on tunnel lining loads, although is important for fill settlement estimates.Peer ReviewedPostprint (author's final draft

La boîte à outils géotechnique de demain: conception des structures géotechniques selon EN 1997: 202x

This paper shows how three new concepts – ‘Design Cases’ (introduced in prEN 1990), the ‘Geotechnical Design Model’ (prEN 1997-1), and the ‘Ground Model’ (prEN 1997-2) – are combined (in prEN 1997-3) to provide a comprehensive and flexible set of tools for the design of specific geotechnical structures. The paper presents flow charts divided between: a) reliability management, b) ground modelling, c) verification of the design, and d) structure execution, which provide guidelines for navigating prEN 1990 and prEN 1997.Postprint (published version

DEM simulation of soil-tool interaction under extraterrestrial environmental effects

In contrast to terrestrial environment, the harsh lunar environment conditions include lower gravity acceleration, ultra-high vacuum and high (low) temperature in the daytime (night-time). This paper focuses on the effects of those mentioned features on soil cutting tests, a simplified excavation test, to reduce the risk of lunar excavation missions. Soil behavior and blade performance were analyzed under different environmental conditions. The results show that: (1) the cutting resistance and the energy consumption increase linearly with the gravity. The bending moment has a bigger increasing rate in low gravity fields due to a decreasing moment arm; (2) the cutting resistance, energy consumption and bending moment increase significantly because of the raised soil strength on the lunar environment, especially in low gravity fields. Under the lunar environment, the proportions of cutting resistance, bending moment and energy consumption due to the effect of the van der Waals forces are significant. Thus, they should be taken into consideration when planning excavations on the Moon. Therefore, considering that the maximum frictional force between the excavator and the lunar surface is proportional to the gravity acceleration, the same excavator that works efficiently on the Earth may not be able to work properly on the Moon.Peer ReviewedPostprint (author's final draft

THM analysis of compacted clay liner response to baled municipal waste

Heat is generated in municipal waste containment facilities due to the chemical and biochemical evolution of waste. Sometimes it is required to check if the level of heat generated during the deposit lifetime may damage or reduce the isolating properties of the liners. That verification relies on appropriate evaluation of heat and moisture transfer through the barrier as well as the evolution of stress fields. This paper presents an example of such verification based on a coupled thermo-hydro-mechanical (THM) analysis for the case of a compacted clay liner designed to isolate a deposit of baled municipal waste. The evaluation of the different boundary conditions for the analysis is discussed in detail. The case study corresponds to a deposit of baled waste and the evaluation of thermal loadings on the lining is performed using thermal discrete elements.Postprint (published version

High resolution incremental stress testing of crushable granular materials

The incremental behaviour of crushable sands is investigated by means of a Discrete Element Method (DEM) based analogue. The DEM sample is subjected to a comprehensive set of small stress perturbations in the triaxial plane in order to identify the basic mechanisms contributing to the corresponding strain response. Three contributions to incremental strains are distinguished: elastic, plastic-structural and plastic-crushing. The behaviour observed appears to be consistent with the classic tenets of elasto-plasticity. It is also shown that high resolution probing is required to identify significant features such as elastic anisotropy and irreversible effects on the tangent bulk and shear moduli. As a consequence, computational efficiency is therefore a must for numerical studies of incremental response.Postprint (published version