Physical model tests on cemented classified tailings and sand backfills have been carried out to determine the strength requirements for stability when vertical fill faces are exposed. The results of this laboratory scale model testing support a three-dimensional analytical solution developed in the paper, whereby the cement strength requirement can be reduced when rock walls are sufficiently close together to help support the backfill by shearing stresses at the wall-backfill contact.Comparisons with conventional backfill strength design approaches show that substantial reductions in cement usage can be realized by using the three-dimensional design approach, particularly when blast hole stoping can be carried out to heights several times greater than the lateral stoping dimensions.Physical modelling of cemented backfills is discussed in detail in the paper and it is concluded that field scale model testing could be useful in the design stages of the development of mining methods at individual mines.Des essais sur modtles physiques ont Ct C rCalisCs sur des stCriles classCs et des remplissages de sable cimentCs pour dtterminer les rksistrtnces requises pour assurer la stabilitC de faces verticales de remplissage. Les rCsultats de ces essais sur modkle en laboratoire concordent avec une solution analytique tri-dimensionnelle dCveloppCe dans l'article, selon laquelle la rksistance de cimentation requise peut Ctre rCduite lorsque les parois rocheuses sont suffisamment rapprochCes pour contribuer au support du remplissage par I'interrnCdiaire des contraintes de cisaillement au contact roc-remplissage.Les comparaisons avec les mCthodes usuelles de calcul de la rksistance de remplissages montrent que des reductions substantielles des quantitCs de ciment sont possibles en utilisant la mCthode tridimensionnelle, en particulier lorsque la hauteur des cheminCes est &gale 21 plusieurs fois leurs dimensions horizontales.La modelisation physique des remplissages cimentCs est discutCe en detail dans l'article et on en conclu que des essais sur modble sur le terrain pourraient Ctre utiles au stade de 1'Ctude des mCthodes d'exploitation de mines particulikres.

A cost effectiveness analysis was performed for equipment, materials, and techniques for the removal of spilled petroleum products from the surface of port and harbor waters used by U. S. Naval craft. Effectiveness criteria, formulated for present methods and presently available equipment and materials, included speed of application, completeness of removal, ease of operation, effect on marine life, operating continuity, and availability. Parameters for the effectiveness study were based on the petroleum products now in use or those planned for future use and a detailed review of the geographic, hydrographic, physical, and environmental characteristics of ports used by the U. S. Navy. The two most cost-effective systems for broad application were found to be mechanical recovery of spilled material by surface suction devices, supplemented by mechanical containment, and the application of chemical dispersants by pier-or vessel-mounted high pressure spray equipment.

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A cost effectiveness analysis was performed for equipment, materials and techniques applicable to the removal or dispersal of spilled oil from U.S. Navy AO and AOG vessels on open waters. Effectiveness parameters included oil product types (JP-5, Distillate Fuel, Navy Special and Bunker C), a range of spill locations (3 and 12 miles frum shore) and varying spill sizes (2,700 gal, 270,000 gal, and 6,750,000 gal). Criteria for evaluation of systems under the above parameter situations, formulated for presently available equipment and materials, included: completeness of oil removal; rate of removal; hazard and pollution; use in limited access areas; sensitivity to expected environmental factors; sensitivity to temperature extremes; toxicity to marine life, and system availability. Cost effectiveness was determined using the 3 spill sizes and checked for spill frequency sensitivity. The three most cost effective systems for the range of spill sizes were found to be burning, dispersing, and mechanical skimming. Considering system applicability to various products and the requirements of rate of removal for massive spills, the mos" practical universal system with a favorable cost effectiveness ratio was found to be dispersing. This is followed by dispersing plus a containment boom. Burning agents applied directly to the spill were judged to be the third best system based on its favorable cost effectiveness but limited applicability to oil types and permissible burning circumstances.