摘要:

Acid production in sulphidic tailings can cause severe degradation of water quality in both subsurface and surface systems. The availability of gaseous oxygen and the rate of diffusion of oxygen through the open pore spaces in the upper zone of the tailings are the critical factors controlling the rate of acid generation. Acid generation can be reduced by applying a fine-grained, nonreactive cover layer to the tailings surface. The key process involves moisture retention by capillary forces so that near-saturated conditions can be maintained even when the cover layer occurs at several metres above the water table. Textured layering of fine over coarse materials improves moisture retention in the fine layer when infiltration exceeds evapotranspiration. The application of such a cover layer can theoretically reduce oxygen diffusion coefficients and rates of acid generation by up to four orders of magnitude. This can represent a substantial difference in the potential treatment costs of tailings seepage. Simplified calculations based on Fick's first law can be applied to preliminary laboratory measurements of diffusion characteristics of potential cover materials to evaluate their effectiveness in decreasing acidification. These concepts and methods provide an initial evaluation before field-scale testing of cover performance.Key words: pyrite oxidation, tailings, remediation, covers, acid generation, oxygen diffusion.

ISSN:0008-3674    

DOI:10.1139/t89-001

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Laboratory freezing tests were performed on a saturated clayey silt at various overconsolidation ratios (OCR) to establish the relationship between initial void ratio and stress history, and the amount of moisture transfer during freezing. The frost heave tests were analysed in terms of the segregation potential as well as a function of the temperature of ice lens formation and the overall hydraulic conductivity of the frozen fringe. All other factors being the same, the segregation potential was found to increase with increasing values of OCR (decreasing initial void ratios). However, the combined effects of decreasing void ratio and increasing suction at the frost line, all other factors being identical in all freezing tests, resulted in decreasing segregation potentials. This trend was the result of a decrease in the temperature of ice lens formation and the concomitant decrease in overall hydraulic conductivity of the frozen fringe. A simple model showed that the capillary unfrozen water between clay particles increases when the particles pack closer together, as overconsolidation increases, allowing the migratory water to freeze within the frozen soil at a colder temperature.Key words: frost heave, clayey silt, overconsolidation, void ratio.

ISSN:0008-3674    

DOI:10.1139/t89-002

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The construction of the Skydome Stadium will provide Toronto with the first multipurpose stadium in the world with a retractable roof. The foundation for the structure, with a diameter of about 210 m and a height of about 86 m, will be supported by several hundred columns, about 100 of which will have loadings up to 50 000 kN. The foundation rock is a shale with numerous highly weathered zones and clay seams. Laboratory tests to investigate the strength and deformation properties of these weak layers were performed. Field plate loading tests at two locations with three different size plates were also carried out to study the size effect on the mass modulus of the rock. This paper presents the results of detailed geological mapping and field and laboratory tests together with design considerations for the foundations. The field acceptance criteria, developed to ensure that the differential settlements between foundations are within specified limits, are also discussed.Key words: Skydome, shale, clay seams, plate loading tests, rock-mass modulus, size effect, layered rocks.

ISSN:0008-3674    

DOI:10.1139/t89-003

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The ultimate bearing capacity of flexible single model piles and small pile groups of timber and nylon in loose sand and soft clay has been determined under various combinations of eccentricity and inclination of the load varying in direction from vertical to horizontal. The results of the load tests are presented in the form of polar bearing capacity diagrams and they are compared with the theoretical estimates based on the concept of an effective embedment depth in terms of the behaviour of equivalent rigid piles. Reasonable agreement has been found between the observed and predicted ultimate bearing capacity of flexible piles under any combination of eccentricity and inclination of loads.Key words: flexible piles, pile groups, ultimate bearing capacity, ultimate moment, model test, eccentric load, inclined load, sand, clay.

ISSN:0008-3674    

DOI:10.1139/t89-004

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The Sarnia area of southwestern Ontario is underlain by thick deposits of clay-rich glacial till. From ground surface to between 4 and 6 m depth the clay till is fractured, oxidized, and penetrated by root holes. The water table fluctuates seasonally between the ground surface and the bottom of the weathered zone. Water-level response tests in conventional piezometers installed in augered holes in the weathered zone typically provide very low values of hydraulic conductivity (10−7–10−9 cm/s), which are similar to values obtained from the deeper unweathered and unfractured till. The augering process creates a smeared clay zone along the borehole walls that significantly reduces measured hydraulic conductivity values. In this study, the weathered-zone hydraulic conductivity was measured using unconventional piezometers, a large-diameter well, and a tracer experiment between two test pits. The smeared zone was removed or reduced around these installations, and the measured weathered-zone hydraulic conductivity was 10−5–10−7 cm/s, much higher than in the deep unweathered clay. These results, together with depth profiles of groundwater tritium and monitored water-level fluctuations, indicate that the weathered zone has hydraulic conductivity governed by fractures and has significant hydrologic activity in the fractures.Key words: clay, fractures, hydraulic conductivity, permeability, piezometer, tritium, tracer experiment, weathered zone.

ISSN:0008-3674    

DOI:10.1139/t89-005

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The interactions of clay particles with alcohol–water mixtures are investigated with hydraulic conductivity measurements, the electrophoretic mobilities of the suspended particles are measured, particle settling tests are carried out, and Atterberg limits are determined. Organic liquids frequently interact with clay particles in the clay liners of surface impoundments. Such fluids can cause changes in hydraulic conductivity of the liner material. This study looks at the effects of dilution of a liquid hydrocarbon with water on the properties of a clay soil. Tests with 20, 40, 60, 80, and 100% (by volume) methanol concentrations are used to investigate the changes in hydraulic conductivity of water-compacted clay samples. Particle settling tests, Atterberg limits, and electrophoretic mobility studies are used with the same concentrations to determine the effects of changing methanol concentration on clay particle behavior. The results indicate that higher concentrations of methanol cause an increase in the attraction between the clay particles, and the same concentrations also cause an increase in hydraulic conductivity.Key words: Atterberg limits, clay, electrophoresis, hydraulic conductivity, methanol, settling tests, zeta potential.

ISSN:0008-3674    

DOI:10.1139/t89-006

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Setbacks from the crests of slopes along the North Saskatchewan River valley between Edmonton and Fort Saskatchewan can be estimated from the ultimate angle of the slope and the rate of lateral river erosion. The ultimate slope angle depends on the slope stratigraphy and the position of the water table in the slope. Three slopes, in overburden, with a bedrock base and dominantly in bedrock, typically having groundwater tables at respectively the toe of the slope, halfway up the slope, and at the lower quarter of the slope height, are studied. Theoretical estimates of the ultimate slope angle in each type, from infinite slope analysis and from charts, agree with observations of the inclinations of abandoned slopes along the river valley. The procedure recommended presents a rational estimation of setback distances without extensive site investigations.Key words: setback, slope, ultimate angle, abandoned slopes, river erosion.

ISSN:0008-3674    

DOI:10.1139/t89-007

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The standard test method used to determine the hydraulic conductivity of a clean granular soil (rigid-wall permeameter –constant head difference) requires that the specimen be saturated with an air-vacuum pump. However, no method is provided to verify whether the sample is fully (100%) saturated. This paper proposes such a method and establishes its accuracy. The method allows for quality control of the rigid-wall permeameter itself: it can detect if it is watertight but not airtight, according to the achieved degree of saturation. A detailed example is given on a proposed data sheet. The reasons for partial saturation and the problems related to air bubbles are examined. The result of this examination is a simplified test to check a permeameter, based on the fact that for unsaturated conditions the hydraulic conductivity depends on which of two ways the water seeps in a given direction. A few modifications in the preparation of the specimen and the test procedure are suggested so as to improve the quality of test results.Key words: permeability, laboratory, granular soils, rigid-wall permeameter, saturation.

ISSN:0008-3674    

DOI:10.1139/t89-008

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

At a site near Montréal, piezometers and core samples were used to assess the origin, age, and rate of groundwater movement in a 28 m thick deposit of Champlain Sea clay.3H occurs only within the upper 3–4 m, which indicates that groundwater below this surficial weathered zone originated prior to 1952. Concentrations of18O, Na+, and Cl−in water from the deepest piezometer suggest that the deep clay was deposited in a mixture of about 33% seawater and 67% freshwater. Profiles of several major ions show a gradual increase in concentration with depth. Mathematical simulations of vertical migration of Ca2+, Mg2+, K+, Na+, and Cl−provide close matches to the field profiles when only upward diffusion of these ions into the surficial freshwater zone is included in the model with a diffusion time of approximately 10 000 a. When the downward advection rate of 0.13 cm ∙ a−1obtained from field measurements of hydraulic gradient and hydraulic conductivity is included in the model, the simulated major-ion profiles deviate markedly from the field profiles. This suggests that the hydraulic gradient in the clay is less than the threshold gradient necessary to cause Darcian flow. This study suggests that, in areas where clayey Champlain Sea deposits are thick, opportunities exist for locating waste disposal facilities that would have no significant potential for causing contamination of groundwater resources beneath the clay.Key words: groundwater, permeability, diffusion, environmental isotopes, threshold gradient, geochemistry, subsurface waste disposa

ISSN:0008-3674    

DOI:10.1139/t89-009

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

This paper describes geotechnical and construction aspects of a water supply tunnel upgrading project, in the Coquitlam River valley, northeast of Vancouver, British Columbia. This tunnel conveys potable water from Coquitlam Lake, a major source of water for the Vancouver area, to below Coquitlam dam, into large-diameter supply mains. This project involved the enlargement of the existing tunnel in rock, and sand and gravel, and the construction of a new tunnel through a wide variety of ground conditions, including stiff silt and clay, sand and gravel with up to 12 m of groundwater head at the tunnel horizon, and granodiorite rock. These difficult ground conditions required careful evaluation of numerous costly excavation methods.The entire project was on a very tight construction schedule, as Coquitlam Lake is an essential source of water during the warm summer months. In total, 786 m of tunnel or decline was driven. To facilitate timely project completion, a decline was driven to intersect the existing tunnel about halfway between the intake and south portal outlet, providing the contractor with two additional faces to work from. Numerous types of ground support were used, including rock bolts, steel sets, and fibre-reinforced shotcrete. Construction was started in July 1986 and completed in May 1987.Key words: tunnel, soft ground, shoring, ground load, rock bolts, shotcrete, blasting.

ISSN:0008-3674    

DOI:10.1139/t89-010

出版商:NRC Research Press    

年代:1989

数据来源: NRC