The paper presents a quantitative assessment of particle orientation, contacts and spatial variation of void ratio in a sand specimen loaded under plane-strain conditions. The specimen has a prismatic shape, and measures 57 mm wide 3 121 mm long 3 180 mm high. It was prepared using a dry natural silica sand known as F-75 Ottawa sand at a dense packing, and was sheared until failure. The specimen failed along a well-defined single shear band. It was then stabilised by slowly percolating a low-viscosity epoxy. Cylindrical subsamples 8 mm in diameter and 50 mm high were cored from the stabilised specimen at regions of interest for further investigation. A synchrotron X-ray microtomography technique was used to acquire high-resolution three-dimensional images of the cores. The scans have a voxel size of 15 . 06 ìm, which is high enough to visualise individual sand particles. Post-scanning analyses included mapping the spatial distribution of void ratio and particle contacts inside and outside the shear band. A good correlation was found between void ratio and particle contacts. Statistical distributions of particle orientation within and outside the shear band were calculated: they show that most particles inside the shear band orient in the x-y plane towards the y-axis, which is perpendicular to the shear band with angle º in the range 70-908. Particles outside the shear band have no preferred orientation in the x-y plane, and form chains with preferred angles of 30-608 from the direction of the applied major principal stress.
A detailed study of spatial variation of void ratio and shear band thickness measurements is presented in this paper. A prismatic sand specimen that initially measured 57 . 4 mm wide 3 120 . 5 mm long 3 182 . 1 mm high was sheared under plane-strain (biaxial) loading conditions. The specimen was prepared at a relative density of 79% using F-75 Ottawa sand. X-ray computed tomography was used to scan the specimen before shearing and after the onset of the shear band. The specimen failed through a single shear band with an inclination angle of 65 . 68 measured from the direction of the minor principal stress. Computer algorithms were developed to calibrate CT images and quantify void ratio (e) variation within the specimen. CT data analysis revealed cross-sectional spatial variation in void ratio where density is higher in regions close to the edges of the specimen due to membrane effects and confining pressure with no significant variation in void ratio in the axial direction (top to bottom) before shearing. The shear band was easily identified from the CT images, and analysis of void ratio showed a noticeable jump in void ratio profile across the shear band. A detailed statistical summary of the thickness of the shear band and variation of void ratio across the shear band is presented and discussed.
This paper presents in-stope measurements of total stress and pore-water pressure at strategic locations within three underground stopes at the Raleigh mine site (Western Australia) that were filled with cemented paste backfill (CPB). The three stopes were very similar in shape. Key differences among the stopes were the filling and resting schedules, the barricade drainage systems used, and the cement content of the CPB. Data from the stopes are compared to determine which controllable factors most significantly influence barricade pressures during and after filling. The most significant factor was the scheduling of rest periods between filling, with even very short pauses in filling dramatically reducing the rate of increase of pore-water pressure and total stress with increasing height of fill.Résumé : Le présent article présente les mesures de contrainte totale et de pression interstitielle effectuées sur le terrain à différents endroits stratégiques, dans trois chambres d'abattage situées dans la mine de Raleigh (Australie-Occidentale) et comblées à l'aide de remblai en pâte de ciment. Ces trois chambres avaient des formes similaires. Les principales différences entre les chambres portaient sur la planification des opérations de remblayage et des périodes d'attente entre chacune de ces opérations, sur les différents systèmes de drainage avec murs de confinement utilisés et sur la teneur en ciment dans le remblai. On a comparé les données obtenues pour chaque chambre afin de déterminer quels facteurs contrôlables influaient le plus sur les valeurs de la pression au niveau des murs de confinement, pendant et après le remblayage. On a constaté que le plus important de ces facteurs était la planification des périodes d'attente entre chaque remblayage et que même de très courtes pauses lors du remblayage réduisaient considérablement le taux d'augmentation de la pression interstitielle et de la contrainte totale à mesure que la hauteur du remblai dans les chambres augmentait. [Traduit par la Rédaction]
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