A discrete numerical description of the mechanical response of soils subjected to degradation by suffusion

Internal erosion is a major cause of the failure of hydraulic earthen structures. A particular case of such an erosion process is suffusion which constitutes a strongly coupled fluid-solid interaction problem. It is a selective erosion of fine particles from an unstable soil structure leaving behind the granular skeleton which possibly leads to deformations. Such a process may cause modification in the mechanical behavior of the soil. To study this problem numerically, a model is established based on the discrete element method implemented in Yade software (Smilauer et al. 2015). Periodic boundary conditions are adopted and the soil is represented by a 3D assembly of spherical discrete elements. Such an oversimplified particle’s shape leads to excessive rolling. To overcome this obstacle, rolling resistance was taken into consideration in the inter-particle contact law. Bearing in mind that numerical modeling of suffusion can constitute a difficult task requiring important computational resources due to the direct description of interactions between solid and liquid phases, a one-way coupling with a fluid phase is considered here. However, effects on the soil due to the loss of a fraction of fine particles is investigated either by modeling soils with different grains size distribution and different initial fines content to characterize its influence on the soil microstructure, or by mimicking the suffusion process by defining an extraction criterion of potentially erodible particles. This extraction criterion is based on the size of the particles, constriction sizes, and the velocity of particles under the effect of fluid forces. From these two approaches, we were able to specify the fines content from which their erosion may have a significant influence on the microstructure. Moreover, the defined extraction criterion was able to describe the effect of erosion on the stability of the soil structure

Impact of Medical Conditions and Medications on Road Traffic Safety

Objectives: Many medical conditions and medicines with therapeutic importance have been shown to impair driving skills, causing road traffic accidents, which leads to great human and economic suffering in Oman. The primary purpose of this study was to assess retrospectively the extent of medical conditions and medications influencing road traffic safety among drivers involved in road accidents. Methods: We conducted a retrospective study among 951 injured or non-injured drivers who reported to Khoula and Nizwa hospitals. We used the Al-Shifa database to find the drivers and contacted randomly selected patients over phone. Results: The majority of victims were male (72.0%), involving personal cars, and reported at Khoula Hospital. The results show that 7.6% of the victimized drivers had a history of medical conditions with diabetes and hypertension (36.1% each) the most common. About 4.0% of victims were on medications of which insulin was the most common (9.4%). Loss of control was contributed to 38.5% of cases followed by dizziness (25.6%), sleep amnesia (10.3%), and blurred vision (7.7%). Other effects blamed by victimized drivers include vertigo, phonophobia, photophobia, back pain, loss of sensation, and headache accounting for 17.9% of cases. Conclusion: Medical conditions and medications influence road traffic safety to some extent in Oman

Modèle numérique discret impliquant un couplage partiel fluide-solide pour décrire les effets de suffusion dans les sols

International audienceSuffusion, a particular case of internal erosion in soils, is a particle-scale mechanism involving the selective erosion of fine particles within the matrix of coarse particles under the effect of water seepage. Modifications in the micro-structure as a consequence of the loss of a fine fraction may affect both the hydraulic and the mechanical properties of the soil. Thus leading, in some cases, to drastic consequences. In this study, a discrete numerical model methodology is introduced to investigate the initiation and development of suffusion as well as to analyse its effects on the soil mechanical properties. For that purpose, an original numerical extraction procedure was developed allowing us to mimic the suffusion process by taking into account both the micro-structure of the granular packing and the hydraulic loading in the suffusion development. Such a procedure is based on a one-way fluid-solid coupling where the interstitial flow is solved with a finite volume approach defined at the pore scale. Numerical soil samples subjected to different hydraulic gradients show that depending on the amount and the role of eroded particles in the granular assembly, the eroded medium either shows negligible deformations during erosion but then collapses suddenly once sheared or it deforms significantly during erosion and recovers part of its strength once subjected to shear forces. A non-linear non-monotonic relation between the eroded mass and the mechanical properties of the soil was found

Modèle numérique discret impliquant un couplage partiel fluide-solide pour décrire les effets de suffusion dans les sols

International audienceSuffusion, a particular case of internal erosion in soils, is a particle-scale mechanism involving the selective erosion of fine particles within the matrix of coarse particles under the effect of water seepage. Modifications in the micro-structure as a consequence of the loss of a fine fraction may affect both the hydraulic and the mechanical properties of the soil. Thus leading, in some cases, to drastic consequences. In this study, a discrete numerical model methodology is introduced to investigate the initiation and development of suffusion as well as to analyse its effects on the soil mechanical properties. For that purpose, an original numerical extraction procedure was developed allowing us to mimic the suffusion process by taking into account both the micro-structure of the granular packing and the hydraulic loading in the suffusion development. Such a procedure is based on a one-way fluid-solid coupling where the interstitial flow is solved with a finite volume approach defined at the pore scale. Numerical soil samples subjected to different hydraulic gradients show that depending on the amount and the role of eroded particles in the granular assembly, the eroded medium either shows negligible deformations during erosion but then collapses suddenly once sheared or it deforms significantly during erosion and recovers part of its strength once subjected to shear forces. A non-linear non-monotonic relation between the eroded mass and the mechanical properties of the soil was found

Une description numérique discrète de la réponse mécanique des sols soumis à une dégradation par suffusion

International audienceInternal erosion is a major cause of the failure of hydraulic earthen structures. A particular case of such an erosion process is suffusion which constitutes a strongly coupled fluid-solid interaction problem. It is a selective erosion of fine particles from an unstable soil structure leaving behind the granular skeleton which possibly leads to deformations. Such a process may cause modification in the mechanical behaviour of the soil. To study this problem numerically, a model is established based on the discrete element method implemented in Yade software (Smilauer et al. 2015). Periodic boundary conditions are adopted and the soil is represented by a 3D assembly of spherical discrete elements. Such an oversimplified particle’s shape leads to excessive rolling. To overcome this obstacle, rolling resistance was taken into consideration in the inter-particle contact law. Bearing in mind that numerical modelling of suffusion can constitute a difficult task requiring important computational resources due to the direct description of interactions between solid and liquid phases, a one-way coupling with a fluid phase is considered here. However, effects on the soil due to the loss of a fraction of fine particles is investigated either by modelling soils with different grains size distribution and different initial fines content to characterize its influence on the soil microstructure, or by mimicking the suffusion process by defining an extraction criterion of potentially erodible particles. This extraction criterion is based on the size of the particles, constriction sizes, and the velocity of particles under the effect of fluid forces. From these two approaches, we were able to specify the fines content from which their erosion may have a significant influence on the microstructure. Moreover, the defined extraction criterion was able to describe the effect of erosion on the stability of the soil structure

A discrete numerical model involving partial fluid-solid coupling to describe suffusion effects in soils

International audienceSuffusion, a particular case of internal erosion in soils, is a particle-scale mechanism involving the selective erosion of fine particles within the matrix of coarse particles under the effect of water seepage. Modifications in the micro-structure as a consequence of the loss of a fine fraction may affect both the hydraulic and the mechanical properties of the soil. Thus leading, in some cases, to drastic consequences. In this study, a discrete numerical model methodology is introduced to investigate the initiation and development of suffusion as well as to analyze its effects on the soil mechanical properties. For that purpose, an original numerical extraction procedure was developed allowing us to mimic the suffusion process by taking into account both the micro-structure of the gran-ular packing and the hydraulic loading in the suffusion development. Such a procedure is based on a one-way fluid-solid coupling where the interstitial flow is solved with a finite volume approach defined at the pore scale. Numerical soil samples subjected to different hydraulic gradients show that depending on the amount and the role of eroded particles in the granular assembly, the eroded medium either shows negligible deformations during erosion but then collapses suddenly once sheared or it deforms significantly during erosion and recovers part of its strength once subjected to shear forces. A non-linear non-monotonic * R. Aboul Hosn relation between the eroded mass and the mechanical properties of the soil was found

Modèle numérique discret impliquant un couplage partiel fluide-solide pour décrire les effets de suffusion dans les sols

International audienceSuffusion, a particular case of internal erosion in soils, is a particle-scale mechanism involving the selective erosion of fine particles within the matrix of coarse particles under the effect of water seepage. Modifications in the micro-structure as a consequence of the loss of a fine fraction may affect both the hydraulic and the mechanical properties of the soil. Thus leading, in some cases, to drastic consequences. In this study, a discrete numerical model methodology is introduced to investigate the initiation and development of suffusion as well as to analyse its effects on the soil mechanical properties. For that purpose, an original numerical extraction procedure was developed allowing us to mimic the suffusion process by taking into account both the micro-structure of the granular packing and the hydraulic loading in the suffusion development. Such a procedure is based on a one-way fluid-solid coupling where the interstitial flow is solved with a finite volume approach defined at the pore scale. Numerical soil samples subjected to different hydraulic gradients show that depending on the amount and the role of eroded particles in the granular assembly, the eroded medium either shows negligible deformations during erosion but then collapses suddenly once sheared or it deforms significantly during erosion and recovers part of its strength once subjected to shear forces. A non-linear non-monotonic relation between the eroded mass and the mechanical properties of the soil was found

Effets de la suffusion sur le comportement mécanique du sol : investigations expérimentales

International audienceThis study presents an experimental approach to investigate the impact of suffusion on the soil's mechanical properties. A newly developed suffusion permeameter is used allowing separate erosion and mechanical tests. The effect of the initial density of the soil on the erosion process is examined. Thereafter, the influence of suffusion on the mechanical properties of the soil is investigated through drained and undrained monotonic triaxial compression tests. The results suggest that the shear strength of eroded soils may either decrease or increase or even may not be affected depending, among others, on the soil's initial density. In addition, in all cases, slightly more dilative volumetric deformations seem to occur during shearing after erosion. Understanding the mechanical behaviour of eroded soils depends on the combined effect of the global void ratio, the inter-granular void ratio and the final fines content after suffusion. Taking into account such a combined effect, an approach to estimate the shear strength of eroded soils is proposed