A laboratory study of anisotropic geomaterials incorporating recent micromechanical understanding

This paper presents an experimental investigation revisiting the anisotropic stress–strain–strength behaviour of geomaterials in drained monotonic shear using hollow cylinder apparatus. The test programme has been designed to cover the effect of material anisotropy, preshearing, material density and intermediate principal stress on the behaviour of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. This paper explains phenomenological observations based on recently acquired understanding in micromechanics, with attention focused on strength anisotropy and deformation non-coaxiality, i.e. non-coincidence between the principal stress direction and the principal strain rate direction. The test results demonstrate that the effects of initial anisotropy produced during sample preparation are significant. The stress–strain–strength behaviour of the specimen shows strong dependence on the principal stress direction. Preloading history, material density and particle shape are also found to be influential. In particular, it was found that non-coaxiality is more significant in presheared specimens. The observations on the strength anisotropy and deformation non-coaxiality were explained based on the stress–force–fabric relationship. It was observed that intermediate principal stress parameter b(b = (σ2 − σ3)/(σ1 − σ3)) has a significant effect on the non-coaxiality of sand. The lower the b-value, the higher the degree of non-coaxiality is induced. Visual inspection of shear band formed at the end of HCA testing has also been presented. The inclinations of the shear bands at different loading directions can be predicted well by taking account of the relative direction of the mobilized planes to the bedding plane

Epidemiological Survey on Trypanosoma evansi Infection in Vietnam

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Investigating the Dynamic Instabilities of Model Granular Materials in Isotropic Consolidation and Triaxial Drained Compression

International audienceThis paper reports the dynamic instabilities of model granular materials under isotropic consolidation and triaxial drained axisymmetric compression. Loose and fully saturated samples of mono sized glass beads exhibit in isotropic drained compression a series of local collapses under undetermined stress and even liquefaction in some rare cases. Stick-slip phenomenon occurs in drained compression, and even rare liquefaction happens for the first slip. These dynamic instabilities (collapse, liquefaction and stick-slip) of loose granular assembly can share the same physical driving mechanisms with strong links to geometrical features, i.e. the collapse of the structural metastable honeycombed macropores or the propagation of the local failures of the force chains; even if the unambiguous identification of the triggering mechanisms is still unknown. The experimental data eliminates the excess pore fluid as the primary cause

Paragonimus westermani and Paragonimus species

Paragonimiasis is a zoonotic food-borne lung disease caused by lung flukes of the genus Paragonimus and acquired by consumption of raw/undercooked freshwater crabs/crayfish or wild boar meat. Paragonimus westermani is the best known species to infect humans in Asia, but several other species of human pathogens are also present. Molecular phylogenetic analyses assign most Asian Paragonimus species into four species complexes with some correlation to human pathogenesis. Paragonimus species exploit a range of mammalian definitive hosts and, as intermediate hosts, freshwater snails and crustaceans, eradication of which is not feasible. Avoidance of consumption of raw/undercooked foods and early diagnosis/treatment are recommended for the control of this disease

On the role of pore pressure in dynamic instabilities of saturated model granular materials

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