A clumped particle model for rock

Keywords: Mecanique des sols ; Drainage ; Ecoulement souterrain Reference Record created on 2004-09-07, modified on 2016-08-08

Applications of soil physics.

A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

An extended model for void growth and coalescence - application to anisotropic ductile fracture

Specimens prepared from eight natural clayey soils used for clay liners and covers were subjected to cycles of wetting and drying. Volumetric shrinkage strains were recorded during drying. Specimens in which cracks formed during drying were subjected to hydraulic conductivity testing. Results of the study indicate that volumetric shrinkage strains are influenced by soil properties and compaction conditions. Volumetric shrinkage strain increased with increasing plasticity index and clay content, and as the compaction water content increased or decreased relative to optimum water content. Volumetric shrinkage strain decreased with increasing compactive effort. Specimens with the largest volumetric shrinkage strains typically contained the largest number of cracks. Hydraulic conductivity testing indicated that cracking of the specimens resulted in an increase in hydraulic conductivity, sometimes as large as three orders of magnitude.

Effect of Desiccation on Compacted Natural Clays

Discrete element models for non-spherical particle systems: From theoretical developments to applications

The objective of this study was to investigate the feasibility of using shredded waste tires to reinforce sand. Direct shear tests were conducted on mixtures of dry sand and shredded waste tires. The following factors were studied to evaluate their influence on shear strength: normal stress, sand matrix unit weight, shred content, shred length, and shred orientation. From results of the tests, three significant factors affecting shear strength were identified: normal stress, shred content, and sand matrix unit weight. A model for estimating the strength of reinforced soils was also evaluated to determine its applicability to mixtures of sand and tire shreds. When the model is calibrated using results from one shred content, it may be useful for estimating the friction angle for other shred contents. In all cases, adding shredded tires increased the shear strength of sand, with an apparent friction angle (ϕ′) as large as 67° being obtained. Shred content and sand matrix unit weight were the most significan...

Sand Reinforced with Shredded Waste Tires

This paper describes research undertaken to develop design procedures for using shredded scrap tires as a lightweight fill material in highway construction. The benefits of using scrap tires are particularly enhanced if they can be used to replace virgin construction materials made from nonrenewable resources. This paper addresses the use of tire chips as a highway embankment material. Design parameters for embankments constructed using discarded shredded tires are presented based on laboratory model studies, numerical analyses, and field performance of test fills. The conclusions of this report support the use of tire chips as an environmentally acceptable lightweight fill in highway applications if properly confined. Recommendations for design procedures and construction specifications for the use of tire chips in highway fills are provided.

Design of Highway Embankments Using Tire Chips

An enhanced discrete element method for the numerical modelling of particulate media is presented. This method models a particle of general shape by combining several smaller particles of simpler shape, such as a circle, into clusters that act as a single larger particle. The clusters more accurately model the geometry- dependent behaviour of the particles, such as particle interlock and resistance to rolling. The method is implemented within the framework of an existing DEM program without the introduction of new contact or force algorithms. An extensive set of numerical ‘experiments’ is performed which demonstrate the method's effectiveness. The granular media–structure interface shear test simulations are performed using both clustered and non-clustered particles. The results indicate that the clustered particles undergo less rolling and provide for increased shear resistance of the medium. Copyright © 1999 John Wiley & Sons, Ltd.

DEM simulation of granular media—structure interface: effects of surface roughness and particle shape

Water balance simulations were conducted with the unsaturated flow model UNSAT-H to assess how layer thicknesses, unsaturated hydraulic properties, and climate affect the performance of capillary barriers Simulations were conducted for four locations in semiarid or arid climates Hydraulic properties of four finer-grained and two coarser-grained soils were selected to study how saturated and unsaturated hydraulic properties affect the water balance Results of the simulations indicate that thickness and hydraulic properties of the surface layer significantly affect the water balance of capillary barriers As expected, increasing the thickness or reducing the saturated hydraulic conductivity of the finer-grained surface layer reduces percolation Unsaturated hydraulic properties of the coarser layer also affect the water balance, including the storage capacity of the surface layer as well as the onset and amount of percolation from the cover Thickness of the coarser layer has a much smaller impact on the water balance Climate also affects the water balance Greater soil water storage capacity is required at sites where the season with more frequent and less intense precipitation does not coincide with the season having highest evapotranspiration

Capillary Barriers: Design Variables and Water Balance

Hydrologic data measured from two earthen final cover test sections constructed on actual landfill final covers are presented with predictions made using two water balance models (HELP and UNSAT-H). Both test sections were constructed as traditional resistive barriers comprised of a compacted fine-grained layer overlain by a vegetated surface layer. Hydrologic and meteorological data including precipitation, air temperature, solar radiation, relative humidity, wind speed, and wind direction were collected at each test section for three years. Percolation, overland flow, and soil water content were monitored continuously. Predictions of the water balance were made using the water balance models HELP and UNSAT-H. In general, HELP overpredicted percolation, sometimes significantly, and UNSAT-H slightly underpredicted percolation. However, both models captured the seasonal variations in overland flow, evapotranspiration, soil water storage, and percolation. UNSAT-H captured these variations more accurately than HELP.

Peter J. Bosscher

Papers

Sand Reinforced with Shredded Waste Tires

Design of Highway Embankments Using Tire Chips

DEM simulation of granular media—structure interface: effects of surface roughness and particle shape

Capillary Barriers: Design Variables and Water Balance

Water Balance Modeling of Earthen Final Covers