摘要:

This paper presents results of centrifugal modelling of physical nonequilibrium transport of nonsorbing solute in a locally inhomogeneous soil. Mathematical modelling of this class of transport process is restricted by the difficulties in determining the model parameters. The modelling results suggest that physical modelling on a geotechnical centrifuge may offer another approach to tackle this problem under certain conditions.Key words: tracer transport, centrifuge, physical modelling, heterogeneous soil, two-region model, scaling.

ISSN:0008-3674    

DOI:10.1139/t94-056

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Compacted bentonites are attracting greater attention as back-filling (buffer) materials for repositories of high-level nuclear waste. However, since there are few studies about the swelling characteristics of compacted bentonites, it is first necessary to clarify the fundamental swelling characteristics in detail. For this purpose, various laboratory tests on the swelling deformation and swelling pressure of compacted bentonites were performed and the results analyzed. The following conclusions were drawn from the study. (i) The curve of swelling deformation versus time is strongly dependent on the initial dry density, vertical pressure, and initial water content. The maximum swelling deformation, however, is almost independent of initial water content, and the maximum swelling deformation increases in proportion to the initial dry density, (ii) The maximum swelling pressure increases exponentially with increasing initial dry density, whereas the maximum swelling pressure is almost independent of initial water content. (iii) The swelling mechanism of compacted bentonite was considered on the basis of the swelling behavior of swelling clay particles such as montmorillonite. Furthermore, a model of the swelling characteristics and a new parameter (swelling volumetric strain of montmorillonite), which were able to evaluate the swelling characteristics of compacted bentonite, were proposed.Key words: bentonite, laboratory test, nuclear waste disposal, swelling deformation, swelling pressure.

ISSN:0008-3674    

DOI:10.1139/t94-057

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Although desirable for many reasons, controlled low-strength material – controlled density fill (nonshrinkable fill) has the potential to promote rapid frost penetration within the trench when used as a backfill material in waterworks construction and repair projects. This paper describes results of a two-dimensional finite-element heat-transfer model study carried out to investigate the effectiveness of various insulation systems for frost and frost-heave protection of buried waterlines. Combinations of nonshrinkable fill with horizontal insulation boards, cylindrical pipe insulation, and inverted U-shaped insulations were investigated. It was shown that, while moderate thicknesses of insulation could be found to protect the pipe from freezing, thermal-bridging effects make the location of the maximum frost penetration depth sensitive to details of the insulation geometry. The use of different combinations of insulating backfills was also investigated, and it was shown that a backfill layer of moderate insulating value placed high in the trench may be most advantageous.Key words: frost, frost protection, insulation, waterlines, nonshrinkable fill, numerical analysis.

ISSN:0008-3674    

DOI:10.1139/t94-058

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Since 1985 natrojarosite residue (NaFe3(SO4)2(OH)6) from the zinc refinery at Kidd Creek near Timmins, Ontario, has been disposed of with mine tailings containing up to 25 wt.% pyrite. Pore-water geochemical data have been collected from depth profiles through the vadose and saturated zones in the tailings. Three zones are defined by the concentrations of metals, SO4, and HCO3. In the deepest zone the concentrations of most metals and anions are below detection and the concentrations of Fe, Mg, Na, K, Zn, Mn, HCO3, and SO4are low, similar to those in the mill discharge water. Higher concentrations of Na, K, Fe, Mg, Mn, Zn, Pb, As, SO4, and HCO3occur within an intermediate zone. These increased concentrations are attributed to natrojarosite dissolution. A surficial zone affected by sulphide oxidation contains high concentrations of metals and SO4. High concentrations of Cd, Co, Cu, Ni, Cr, and Al in this zone characterize the effects of sulphide oxidation on pore-water composition as distinct from the effects of natrojarosite dissolution. The H+released by Fe3+hydrolysis following natrojarosite dissolution is neutralized by carbonate-mineral dissolution that reduces the acid-neutralization capacity of the tailings and releases HCO3. Natrojarosite codisposal with tailings also causes deterioration of the pore-water quality because the dissolution of natrojarosite releases Na, K, Fe, Pb, and SO4to the pore water.Key words: mine tailings, natrojarosite, jarosite, tailings geochemistry, sulphide oxidation.

ISSN:0008-3674    

DOI:10.1139/t94-059

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The lateral soil pressures, bending moments, pile displacements at ground surface, and bearing capacity of instrumented vertical single flexible model piles in layered sands consisting of loose sand overlying compact sand under vertical eccentric and central inclined loads have been investigated. The results of these load tests are compared with theoretical estimates based on the concept of an effective embedment depth of equivalent rigid piles. Reasonable agreement has been found between the observed and predicted behaviour of flexible piles. The analyses are also compared with the results of some field case records.Key words: bearing capacity, instrumentation, model test, layered soil, pile, sand.

ISSN:0008-3674    

DOI:10.1139/t94-060

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The soil-water characteristic curve can be used to estimate various parameters used to describe unsaturated soil behaviour. A general equation for the soil-water characteristic curve is proposed. A nonlinear, least-squares computer program is used to determine the best-fit parameters for experimental data presented in the literature. The equation is based on the assumption that the shape of the soil-water characteristic curve is dependent upon the pore-size distribution of the soil (i.e., the desaturation is a function of the pore-size distribution). The equation has the form of an integrated frequency distribution curve. The equation provides a good fit for sand, silt, and clay soils over the entire suction range from 0 to 106 kPa.Key words: soil-water characteristic curve, pore-size distribution, nonlinear curve fitting, soil suction, water content.

ISSN:0008-3674    

DOI:10.1139/t94-061

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 106 kPa), was proposed by the first two authors in another paper. This equation is used to predict the coefficient of permeability for unsaturated soils. By using this equation, an evaluation of the residual water content is no longer required in the prediction of the coefficient of permeability. The proposed permeability function is an integration form of the suction versus water content relationship. The proposed equation has been best fit with example data from the literature where both the soil-water characteristic curve and the coefficient of permeability were measured. The fit between the data and the theory was excellent. It was found that the integration can be done from zero water content to the saturated water content. Therefore, it is possible to use the normalized water content (volumetric or gravimetric) or the degree of saturation data versus suction in the prediction of the permeability function.Key words: coefficient of permeability, soil-water characteristic curve, unsaturated soil, water content, soil suction.

ISSN:0008-3674    

DOI:10.1139/t94-062

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Track quality rating systems are briefly introduced as a background for undertaking a study of the repeated-load response of ballast aggregates. The results from a number of different laboratory investigations are reviewed and this data interpreted in terms of track quality behaviour. The paper reviews selected results from repeated-load triaxial tests used to investigate the repeated-loading response of different granular railway ballasts at stress levels comparable with those below North America heavy freight axle loads. These results are used to establish an aggregate index to predict deformation and breakdown of ballast under repeated loading. Large-scale test programs are reviewed that relate aggregate quality to simulated ballasted track formation response using a 0.9 m long by 250 mm wide tie to represent a typical loaded rail seat. The large-scale testing was restricted to one aggregate that was subjected to a range of load levels and artificial subgrade stiffness. Similar related work on coarse, single-sized aggregates recommended for drainage layers in highway pavements is reviewed to illustrate the trade-offs between support compressibility and quality of aggregate defined by the aggregate index value. The laboratory tests and model performance are compared with published data to establish a laboratory performance rating in the form of an aggregate index for prediction of those track quality indices that relate to deformation as a function of aggregate type.Key words: ballast, aggregate, hardness, toughness, railway, track quality.

ISSN:0008-3674    

DOI:10.1139/t94-063

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Criteria for soil retention and permeability are important in the proper selection of a geotextile in filtration design. Gradient-ratio tests have been performed to assess the compatibility of nonwoven geotextiles with soils exhibiting a range of gradations. Observations of any soil piping through a geotextile were used to evaluate soil-retention criteria. The American Society for Testing and Materials test apparatus includes additional ports that were used to define a modified gradient ratio, which is a better indicator of flow condition. Measurements of the distribution of water head through the soil sample and geotextile specimen, and its variation with imposed hydraulic gradient and time, are used to establish the permeability of the soil and soil–geotextile composite. The composite layer is relatively thin. A unified interpretation of the results is presented that shows a gradient ratio greater than one means the permeability of the composite is less than that of the protected soil: the condition is acceptable if it can be demonstrated that no impediment of seepage flow will result.Key words: filtration, geotextile, soil retention, gradient ratio, permeability.

ISSN:0008-3674    

DOI:10.1139/t94-064

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Field data are reported that describe the load–strain–time relationship of geogrid reinforcement in a reinforced soil structure. The data are for a period exceeding 5 years and reveal a continued strain in the reinforcement, which occurs at nearly constant load. The response to loading is attributed to creep of the polymeric material. A comparison of the field data with laboratory isochronous load–strain curves, from rapid loading creep tests performed at a temperature similar to the mean annual temperature in the backfill soil, shows the curves describe very well the magnitude of creep strains observed in the field. Implications of the load–strain–time performance data are assessed with reference to the use in design of a tensile strength established from the rapid-loading creep test and wide-width strip test. The need to clarify, in design of polymeric reinforced soil structures, between a safe and allowable tensile strength is emphasized.Key words: reinforced soil, geogrid, creep, tensile strength, strain.

ISSN:0008-3674    

DOI:10.1139/t94-065

出版商:NRC Research Press    

年代:1994

数据来源: NRC