Modelling soil-water interaction with the Material Point Method. Evaluation of single-point and double-point formulations

Many problems in geotechnical engineering involve large deformations and soil-water interactions, which pose challenging issues in computational geomechanics. In the last decade, the Material Point Method (MPM) has been successfully applied in a number of large-deformation geotechnical problems and multi-phase MPM formulations have been recently proposed. In particular, there exist two advanced coupled hy-dro-mechanical MPM approaches to model the interaction between solid grains and pore fluids: the single-point and the double-point formulation. The first discretizes the soil-water mixture with a single set of ma-terial points (MP) which moves according to the solid velocity field. The latter uses two sets of MP one for the fluid phase and the other for the solid phase and they move according to the respective velocity field. The aims of this work is to present and compare the two theories, to emphasize their limitations and poten-tialities, and to discuss their applicability in the geotechnical field. To this end, the results of two numerical examples carried out by using both formulations are presented: a 1D-consolidation problem and a saturated column collapse problem

MarsBots: Robotic Learning Module

This learning module offers hands-on, minds-on activities investigating the Martian environment and robotic technologies of space exploration. The learning module contains 16 national standards-based lessons designed to progress logically from learning about Mars and why scientists and engineers want to explore Mars with robots (lessons 1 through 8) to the fundamental principles of robotics and how these principles are applied to design, construct, and test robotic explorer (lessons 9 through 16). The module is integrated to support fundamental concepts and skills in language arts, mathematics, and science. A background section along with teacher notes provide information needed to present each lesson. Educational levels: Intermediate elementary

Inside Magazine, October 2010

Iowa Department of Transportation Newsletter. INSIDE Magazine is developed to help keep all Iowa DOT employees informed about critical issues affecting them, recognize DOT employees for their excellent service and share interesting aspects in the lives of our co-workers

Discrete modelling of capillary mechanisms in multi-phase granular media

A numerical study of multi-phase granular materials based upon micro-mechanical modelling is proposed. Discrete element simulations are used to investigate capillary induced effects on the friction properties of a granular assembly in the pendular regime. Capillary forces are described at the local scale through the Young-Laplace equation and are superimposed to the standard dry particle interaction usually well simulated through an elastic-plastic relationship. Both effects of the pressure difference between liquid and gas phases and of the surface tension at the interface are integrated into the interaction model. Hydraulic hysteresis is accounted for based on the possible mechanism of formation and breakage of capillary menisci at contacts. In order to upscale the interparticular model, triaxial loading paths are simulated on a granular assembly and the results interpreted through the Mohr-Coulomb criterion. The micro-mechanical approach is validated with a capillary cohesion induced at the macroscopic scale. It is shown that interparticular menisci contribute to the soil resistance by increasing normal forces at contacts. In addition, more than the capillary pressure level or the degree of saturation, our findings highlight the importance of the density number of liquid bonds on the overall behaviour of the material

On the capillary stress tensor in wet granular materials

This paper presents a micromechanical study of unsaturated granular media in the pendular regime, based upon numerical experiments using the discrete element method, compared to a microstructural elastoplastic model. Water effects are taken into account by adding capillary menisci at contacts and their consequences in terms of force and water volume are studied. Simulations of triaxial compression tests are used to investigate both macro and micro-effects of a partial saturation. The results provided by the two methods appear to be in good agreement, reproducing the major trends of a partially saturated granular assembly, such as the increase in the shear strength and the hardening with suction. Moreover, a capillary stress tensor is exhibited from capillary forces by using homogenisation techniques. Both macroscopic and microscopic considerations emphasize an induced anisotropy of the capillary stress tensor in relation with the pore fluid distribution inside the material. In so far as the tensorial nature of this fluid fabric implies shear effects on the solid phase associated with suction, a comparison has been made with the standard equivalent pore pressure assumption. It is shown that water effects induce microstrural phenomena that cannot be considered at the macro level, particularly when dealing with material history. Thus, the study points out that unsaturated soil stress definitions should include, besides the macroscopic stresses such as the total stress, the microscopic interparticle stresses such as the ones resulting from capillary forces, in order to interpret more precisely the implications of the pore fluid on the mechanical behaviour of granular materials.Comment: 39 page

Digital vs. Print: Reading Comprehension and the Future of the Book

The future of books and libraries is put into question by the increasing popularity of e-books and the use of computers as text platforms. In an effort to anticipate which reading platform—print, e-readers, or computers displays—will dominate in the coming years, recent research and experimental data on the suitability of each reading platform for reading comprehension will be considered, from the perspectives of optical issues, cognition, and metacognition. It will be shown that, while printed books are most conducive to learning from longer, more difficult texts, e-readers and computer displays offer convenience and some distinct advantages to readers in particular situations. This synthesis of current research will be helpful to librarians working in digital and print book purchasing and collection development, as well as those making long-range planning decisions

Effect of flow pattern at pipe bends on corrosion behaviour of low carbon steek and its challenges

Recent design work regarding seawater flow lines has emphasized the need to identify, develop, and verify critical relationships between corrosion prediction and flow regime mechanisms at pipe bend. In practice this often reduces to an pragmatic interpretation of the effects of corrosion mechanisms at pipe bends. Most importantly the identification of positions or sites, within the internal surface contact areas where the maximum corrosion stimulus may be expected to occur, thereby allowing better understanding, mitigation, monitoring and corrosion control over the life cycle. Some case histories have been reviewed in this context, and the interaction between corrosion mechanisms and flow patterns closely determined, and in some cases correlated. Since the actual relationships are complex, it was determined that a risk based decision making process using selected ‘what’ if corrosion analyses linked to ‘what if’ flow assurance analyses was the best way forward. Using this in methodology, and pertinent field data exchange, it is postulated that significant improvements in corrosion prediction can be made. This paper outlines the approach used and shows how related corrosion modelling software data such as that available from corrosion models Norsok M5006, and Cassandra to parallel computational flow modelling in a targeted manner can generate very noteworthy results, and considerably more viable trends for corrosion control guidance. It is postulated that the normally associated lack of agreement between corrosion modelling and field experience, is more likely due to inadequate consideration of corrosion stimulating flow regime data, rather than limitations of the corrosion modelling. Applications of flow visualization studies as well as computations with the k-ε model of turbulence have identified flow features and regions where metal loss is a maximu

A time-dependent anisotropic model for argillaceous rocks: application to an underground excavation in Callovo-Oxfordian claystone

The paper presents a constitutive model for argillaceous rocks, developed within the framework of elastoplasticity, that includes a number of features that are relevant for a satisfactory description of their hydromechanical behaviour: anisotropy of strength and stiffness, behaviour nonlinearity and occurrence of plastic strains prior to peak strength, significant softening after peak, time-dependent creep deformations and permeability increase due to damage. Both saturated and unsaturated conditions are envisaged. The constitutive model is then applied to the simulation of triaxial and creep tests on Callovo-Oxfordian (COx) claystone. Although the main objective has been the simulation of the COx claystone behaviour, the model can be readily used for other argillaceous materials. The constitutive model developed is then applied, via a suitable coupled hydromechanical formulation, to the analysis of the excavation of a drift in the Meuse/Haute-Marne Underground Research Laboratory. The pattern of observed pore water pressures and displacements, as well as the shape and extent of the damaged zone, are generally satisfactorily reproduced. The relevance and importance of rock anisotropy and of the development of a damaged zone around the excavations are clearly demonstrated.Peer ReviewedPostprint (author's final draft