摘要:

An experimental study on electrokinetic sedimentation of contaminated sediment is conducted. The sediment dredged from the Welland River in Ontario is heavily contaminated by metals, oil, and grease as a result of industrial activities over past decades. Characterization of the sediment is presented, followed by descriptions of the sedimentation columns used in the experiments and testing procedure. The application of electrokinetics on the Welland River sediment suspensions significantly increases the free settling velocity (up to 110%) and final solid concentration (up to 33%) and reduces the coefficient of sedimentation (up to 111%) and overall sedimentation time (up to 50%). These changes are functions of the initial solid concentration and applied electric field intensity. Based on the evaluation of all influencing factors, it is concluded that a continuous dc current generates better performance than intermittent current and electrokinetic sedimentation is more effective than chemical coagulation. All other conditions being equal, the combined application of electrokinetics and FeCl3generated the best dewatering effect. The electrokinetic treatment generates pH changes ranging from pH 6.0 at the anode to pH 9.4 at the cathode which will generate a negligible environmental impact, as most metal contaminants will not be released to water in this pH range.Key words: electrophoresis, electrokinetics, sedimentation, contaminated sediment, waste management.

ISSN:0008-3674    

DOI:10.1139/t00-017

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper reports the experimental study and modelling of the mechanical response of a silty sand used in the core of the Metramo dam, Italy. Specimens were prepared by compacting the soil at optimum water content conditions using the modified Proctor technique. Tests were performed under suction-controlled conditions by a stress path triaxial cell and an oedometer. The experimental program consists of 23 tests carried out in the suction range of 0-400 kPa. The findings indicate the strong influence of suction on compressibility, stiffness, and shear strength. The mechanical properties of the soil improve with suction following an exponential law with decreasing gradient. Furthermore, the soil exhibited collapsible behaviour upon wetting even at low stress levels. Interesting results were also achieved in elastoplastic modelling as well. The results led to characterization of soil behaviour with reference to widely accepted modelling criteria for unsaturated soils, providing noteworthy suggestions about their applicability for granular materials with a non-negligible fine component. Finally, some remarks are made for the extension under unsaturated conditions of the "Nor sand" model for saturated granular soils. The proposed approach yields improved predictions of deviator soil response of the tested soil when Cambridge-type frameworks prove invalid.Key words: unsaturated soils, stress state variables, triaxial tests, oedometer tests, constitutive model.

ISSN:0008-3674    

DOI:10.1139/t00-004

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper presents the findings of a laboratory investigation of the thermomechanical behaviour of clayey soils. The tests were performed on reconstituted and natural clayey soils using triaxial cells modified to control temperature. The range of temperatures that were investigated is from 20° to 60°C. The thermal behaviour of the clays and the influence of temperature on their mechanical behaviour were investigated separately. The analysis of the experimental results obtained in drained and undrained nonisothermal tests and during thermal consolidation made it possible to identify a link between the thermal and the time-dependent behaviour of the soil skeleton. Therefore, as for creep processes, the response of the soil to thermal loading is not unique but among other factors depends strongly on the overall and recent stress history experienced by the soil. In the range of temperatures investigated, the deformability and strength of the soil were found to be relatively independent of temperature. Stiffening of the soil results from thermal cycles.Key words: clay, temperature, creep, stress history, recent stress histor

ISSN:0008-3674    

DOI:10.1139/t00-010

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The paper describes a mechanics-based methodology for prediction of landslide hazard on hillside slopes. The principal components are estimation of infiltration and groundwater response, and estimation of safety factor and failure probability. Predictions with the models are made by using the best estimates of the input parameters and the associated uncertainties. The uncertainties about the inputs and the sensitivities of the model outputs to uncertainties about the inputs are evaluated and translated into failure probability. Our objective was to provide a method that can be used to estimate landslide hazard over a large area prior to making detailed site investigations. The method was applied to slopes along the South Fork of Tilton River, in the Cascade Mountains of Washington State. Predicted hazards were compared with results of a landslide inventory. The data used in the examples were derived from published sources. However, the procedures developed are not limited to this condition and can readily incorporate additional information derived from more detailed investigations.Key words: failure probability, groundwater, hazard, landslides, mapping, slope stability.

ISSN:0008-3674    

DOI:10.1139/t00-006

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper presents the analyses of the results of the site investigation programme carried out at the Kowloon Bay site in Hong Kong. The tests consisted of self-boring pressuremeter (SBPM), Marchetti dilatometer (DMT), and laboratory tests carried out in a granite saprolite, which can be described as a lightly cemented sand. The purpose of this research project is to stimulate the development of methods to interpret data obtained from tests in residual soils. In particular, the work aims to evaluate the analyses of the SBPM data through a curve-fitting technique. Both the loading and unloading portions of the SBPM curve were analysed and the results compared with those from other tests. The advantage of this analysis technique is the possibility of constructing a theoretical curve that reproduces a pressuremeter test from which a set of fundamental parameters can be derived, namely the friction angle, cohesion intercept, lateral stress, and shear modulus. The DMT proved to be a reliable tool that yielded good soil parameters at a small fraction of the cost of the other in situ tests.Key words: residual soil, in situ tests, pressuremeter, Marchetti dilatometer.

ISSN:0008-3674    

DOI:10.1139/t00-005

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The constitutive models on viscoelastoplasticity and the damage to frozen soil presented in this paper can be used to analyze the relationship of stress and strain, under complicated stress states, and damage development and the failure process of the internal structure of frozen soil. The models successfully predict the whole process of creep, including the failure stage. Both strengthening and weakening effects of confining pressure, namely increasing the friction force between soil particles and decreasing the frozen force between ice and the soil particles due to pressure melting of ice, are considered in the constitutive models.Key words: viscoelastoplasticity, damage development, constitutive model, frozen soil.

ISSN:0008-3674    

DOI:10.1139/t00-014

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

The grain-size distribution is commonly used for soil classification; however, there is also potential to use the grain-size distribution as a basis for estimating soil behaviour. For example, much emphasis has recently been placed on the estimation of the soil-water characteristic curve. Many methods proposed in the literature use the grain-size distribution as a starting point to estimate the soil-water characteristic curve. Two mathematical forms are presented to represent grain-size distribution curves, namely, a unimodal form and a bimodal form. The proposed equations provide methods for accurately representing uniform, well-graded soils, and gap-graded soils. The five-parameter unimodal equation provides a closer fit than previous two-parameter, log-normal equations used to fit uniform and well-graded soils. The unimodal equation also improves representation of the silt- and clay-sized portions of the grain-size distribution curve.Key words: grain-size distribution, sieve analysis, hydrometer analysis, soil classification, probability density function.

ISSN:0008-3674    

DOI:10.1139/t00-015

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

This paper presents the results of a series of plane strain model tests carried out on both reinforced and unreinforced sand slopes loaded with a rigid strip footing. The objectives of this study are to (i) determine the influence of geosynthetic reinforcement on the bearing-capacity characteristics of the footing on slope, (ii) understand the failure mechanism of reinforced slopes, and (iii) suggest an optimum geometry of reinforcement placement. The investigations were carried out by varying the edge distance of the footing for three different slope angles and three different types of geosynthetic. It is shown that the load-settlement behaviour and ultimate bearing capacity of the footing can be considerably improved by the inclusion of a reinforcing layer at the appropriate location in the fill slope. The optimum depth of the reinforcement layer, which resulted in maximum bearing capacity ratio (BCR), is found to be 0.5 times the width of the footing. It is also shown that for both reinforced and unreinforced slopes, the bearing capacity decreases with an increase in slope angle and a decrease in edge distance. At an edge distance of five times the width of the footing, bearing capacity becomes independent of the slope angle. The effectiveness of the geosynthetic in improving the bearing capacity of the footing is attributed to its primary properties such as aperture size and axial stiffness. A numerical study using finite element analyses was carried out to verify the model test results. The agreement between observed and computed results is found to be reasonably good in terms of load-settlement behaviour and optimum geometry of georeinforcement placement.Key words: model tests, footing, bearing capacity, fill slope, finite element method, geosynthetic.

ISSN:0008-3674    

DOI:10.1139/t00-016

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Gas can be found in many soils, but none more common than in seabed soils. Gas-charged sediments are known to be widely distributed throughout the world's oceans. Numerous research programs have studied saturated soil response to cyclic loading; however, little is known about the behavior of gassy soils subjected to cyclic loading. The response of loose gassy specimens subjected to cyclic loading was studied in a laboratory program. Triaxial tests were performed on specimens of reconstituted Ottawa sand prepared to various gas contents and densities. The specimens were consolidated and then sheared under undrained cyclic loading. Gas content was measured at the beginning and end of each test using time domain reflectometry. The response of the gassy specimens has been shown to be influenced by the soil state and grain characteristics and the intensity, duration, and frequency of the cyclic loading. The propensity of a soil to liquefy is represented by a cyclic resistance ratio, defined as the cyclic stress ratio to cause liquefaction, or to cause a specified amount of strain. The results of this laboratory program show that the cyclic resistance ratio increases as gas content and density increase. The laboratory study demonstrates that the cyclic liquefaction potential of a soil is reduced by the addition of gas; however, soils containing some gas may still experience cyclic liquefaction provided they are sufficiently loose.Key words: triaxial testing, cyclic liquefaction, Ottawa sand, gassy, unsaturated.

ISSN:0008-3674    

DOI:10.1139/t00-008

出版商:NRC Research Press    

年代:2000

数据来源: NRC

摘要:

Kaolinite-silt mixtures at different clay contents were subjected to closed-system freezing and thaw consolidation to obtain data on the hydraulic conductivity of thawed samples. A simplified void ratio model was developed based on the compressibility characteristics of the clay aggregates and the freezing-induced suctions. The close agreement between predictions and observations suggests that the assumptions of the model are reasonable, especially that maximum freezing-induced suctions developed in the clay aggregates are related to the temperature at which no significant change in unfrozen water content occurs rather than the actual freezing temperature. Furthermore, the compression characteristics of thawed mixtures is essentially controlled by the recompression of the clay aggregates in the overconsolidated domain. The void ratio model is linked to a permeability model that suggests that the hydraulic conductivity of thawed mixtures can be defined by a reference value of the unfrozen soil and a parameter specific to each mixture.Key words: freeze-thaw, laboratory, hydraulic conductivity, conceptual model, silt, kaolin.

ISSN:0008-3674    

DOI:10.1139/t00-003

出版商:NRC Research Press    

年代:2000

数据来源: NRC