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]

A critical state testing round robin programme was carried out on sandy silt gold tailings. This involved 15 laboratories around the world testing a sandy silt tailings to infer its critical state line (CSL). Methods to be used were intentionally not supplied to participants, to enable the current methods being employed in industry and academia to be obtained in an unbiased manner. All but one of the laboratories involved in the study used the moist tamping sample preparation technique, generally to produce loose, contractive specimens. Void ratio was measured using a variety of means, including cell calibration, end-of-test water content and end-of-test soil freezing (EOTSF) to assist in measuring the final water content. Of the 15 entries, four were excluded from the primary comparison owing to various issues that appear to have led to their divergence from most of the entries received. Of the remaining entries, the best reproducibility was produced by laboratories that used EOTSF to measure void ratio. Most other test procedure variations appeared to have a negligible effect, with the exception of fixing of the top platen and possibly sample size. A CSL elevation range of 0·04 void ratio for laboratories using EOTSF was observed.

A constant-volume direct simple shear apparatus was used to investigate the effects of confining stress, initial static shear stress and void ratio on the liquefaction resistance of fine-grained tailings. The cyclic resistance ratio (also expressed as the overburden stress correction factor) was found to decrease with increasing confining stresses in the range 100–400 kPa and to gradually increase from 400 kPa onwards, when samples were tested at the same initial void ratio. The presence of an initial static shear stress decreased the liquefaction resistance. A key outcome of the work was to reveal the critical importance of density on liquefaction susceptibility of compressible tailings. Thus, a combined correction factor to account for overburden stress and density on cyclic resistance was proposed.

This paper presents full-scale experiments on cemented paste backfilling in two operating mine stopes located at Raleigh mine, Kalgoorlie, Western Australia. The experiments compared the behaviour of the cemented paste backfill (CPB) in a drained stope and an undrained stope. The drained stope was equipped with a drainage system at the barricade, whereas the undrained stope was not. Total stress and pore water pressure sensors were installed to measure the stress within the fill mass during and after backfilling. The stress behaviour was expressed by the normalised total horizontal pressure and the normalised pore water pressure. It was found that the normalised total horizontal pressure and the normalised pore water pressure behaviour at the two stopes were significantly different. The drainage system increased the consolidation of the fill and reduced the pressure acting on the barricade. The pore water pressure measurement in the undrained stope showed a non-linear accumulation at the barricade. In contrast with the undrained stope, the stope with the drainage system showed significant pore water pressure reduction and the accumulation of pore water pressure at the barricade no longer occurred. The findings described in the paper contribute to critical design and management aspects such as barricade stress, filling rate, and curing strategy, with an ultimate goal of reducing costs while ensuring safety underground.

Monitoring of tailings water content using light reflection measurements