摘要:

This paper describes the application of a simplified Winkler model to simulate the observed time-dependent responses of a pipeline at Caen, France, subjected to differential frost heave. The numerical Winkler model developed for a semi-infinite beam embedded in a creeping medium was used to evaluate the response of the Caen pipeline. Despite its simplicity, the Winkler model is able to predict the overall response of deflections and stresses which compares satisfactorily with observed data. In a previous study, the same Winkler analysis was applied to small-scale model steel pipelines embedded in polycrystalline ice, and satisfactory comparisons between the predicted and observed responses were obtained. Consequently, the analyses presented in this paper serve to reconfirm that the Winkler model can also be applied to analyze large-diameter pipelines subjected to differential frost heave.Key words: chilled pipelines, creeping foundation, frozen soils, frost heave.

ISSN:0008-3674    

DOI:10.1139/t94-098

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

For offshore drilling, and in particular when drilling from fixed platforms in deep waters, the mud pressure will be high compared with the hydraulic fracture pressure (i.e., the formation strength) close to the sea floor. The first casing (the conductor) should therefore be installed to a depth where the formation strength is sufficient to prevent hydraulic fracturing of the soil. The consequences of hydraulic fracture could be mud flowing into the formation and loss of mud circulation. This slows down the drilling and, in cases where large quantities of mud flow into the formations beneath the platform, may even threaten the integrity of the foundation soils and create a safety problem. A conservative approach with too deep conductor setting depths will, on the other hand, lead to high unnecessary costs. This paper presents a new approach for calculating hydraulic fracture pressures. The new calculation approach considers two important factors that are generally not covered by theories found in the literature: nonlinearity of the stress–strain properties of the soil, and pore-pressure changes in the soil due to changes in total normal stress and shearing of the soil. The stress–strain properties and the shear-induced pore pressure are determined from laboratory tests. The proposed calculation approach has been verified against a series of laboratory model hydraulic fracture tests and in situ hydraulic fracture tests carried out at numerous offshore sites. The paper also presents a rational approach to establish the maximum allowable drilling mud pressure in clay formations and recommends partial safety coefficients that depend upon the consequences of hydraulic fracture and the quality of the soil data.Key words: hydraulic fracture, boreholes, clay, conductor setting depth, model tests, in situ tests, calculations.

ISSN:0008-3674    

DOI:10.1139/t94-099

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

To optimize the design of erosion-control filters a transport model is presented for moving base material in horizontally loaded filters that are not geometrically stable. Supporting experimental work is used to obtain the parameters in a descriptive quantitative mathematical model. A set of three fixed parameters describes most experiments. Exceptions are where the filter to base grain-size ratio is so small that geometrical obstruction takes place and where this ratio is so large that the turbulences in the flow cause the sand surface under the filter to ripple. The latter case is described with a slightly amended parameter to allow for the amount of fluctuation in the problem.Key words: filtration, transport, experiments, theory, granular material, barriers.

ISSN:0008-3674    

DOI:10.1139/t94-100

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Long-term, drained triaxial creep and direct simple shear creep tests were conducted on undisturbed marine specimens from the Gulf of Mexico and the north-central Pacific. Results indicated that time-dependent deformations can be represented by a power law equation, and the creep strain rate can be represented by an equation similar to that suggested earlier by other researchers. However, it was found that themparameter suggested by these scientists was not a constant but dependent on stress level and sediment plasticity. Ageing effects were evidenced in triaxial specimens by the increase of shear strength with both test duration and stress level. The results provided a guide for the development of mathematical stress–strain–time relationships that will be developed in a separate paper.Key words: drained triaxial creep, simple shear creep, stress–strain–time behavior.

ISSN:0008-3674    

DOI:10.1139/t94-101

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

When a pile is driven into clay, horizontal and vertical movements are developed in the soil surrounding the pile. These movements will tend to develop axial forces and bending moments in adjacent piles that have already been installed. Possible consequences for these piles are (i) structural damage or cracking (of concrete piles) arising from the induced bending moments, (ii) tensile failure of the piles due to the induced axial forces, and (iii) lifting-off of the pile tip from the bearing stratum due to the axial induced movements. This paper describes the results of a theoretical analysis of the bending moments and axial forces developed in a pile due to driving of an adjacent pile in clay. The analysis uses approximate distributions of horizontal and vertical soil movements caused by pile driving, developed from a "strain-path" analysis, together with inferences from model pile test data. An examination is made of various factors that may influence the induced bending moments and forces, including pile spacing, depth of penetration of the adjacent pile, and number of piles driven. For a number of published case histories comparisons are made between theoretical and measured axial and lateral pile movements. In general, satisfactory agreement is found.Key words: foundations, lateral movements, pile driving, settlement, soil displacement.

ISSN:0008-3674    

DOI:10.1139/t94-102

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The paper presents the results obtained in the finite element simulation of 8 years of construction of a section of Syncrude's tailings dyke, which is located in northern Alberta and has been used to store oil sand mining waste. The site investigation for the construction of this dyke indicated that a region of the foundation contained a presheared, overconsolidated clay shale lying practically horizontal at about 20 m depth. Significant horizontal displacements have occurred along this layer. The section analyzed in this work is the one which showed the largest horizontal movements in the foundation. High pore pressures have been measured along this section, and the lateral displacements measured in the foundation have reached values over 25 cm. The major purposes of the finite element analyses were to identify the factors that have significantly influenced the deformation mechanisms and to determine a combination of parameters, within the acceptable range of values for each material, that would reproduce satisfactorily the field observations. Linear, nonlinear, and effective stresses analyses were carried out. The total stress analyses underestimated the displacements measured in the field very significantly. The displacements calculated by the effective stress analyses are in very good agreement with the measured values, and the combination of parameters necessary to reach those results are within the acceptable range of variability for each material involved, based on laboratory test results. The interpolation of the pore pressures based on the piezometer measurements and their incorporation into the analyses as known quantities at each stage of the loading process was found to be relatively simple and efficient, causing a substantial improvement of the results compared with the total stress analyses.Key words: tailing dyke, deformation analysis, shear zone, effective stress modelling, history matching.

ISSN:0008-3674    

DOI:10.1139/t94-103

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Hydrogeological and geochemical investigations were conducted on four fractured Champlain Sea clay deposits in Eastern Ontario. The results from water level monitoring, maximum seasonal variations, and hydraulic head profiles revealed a hydraulically active fractured zone existing at all four sites. The depth of this fractured zone varies from site to site, ranging from 3.2 to 6.0 m. Slug test analysis indicated that bulk hydraulic conductivity values in the upper fractured zone range from 1.8 × 10−8to 2.0 × 10−5 m/s. In contrast, the measured hydraulic conductivity values from the deepest piezometers range from 8.2 × 10−10to 1.4 × 10−9 m/s. The geochemical analysis indicated the presence of three hydrochemical facies: a shallow "active" facies, a deep "inactive" facies, and an intermediate "transition" facies. The presence of tritiated groundwater well below the groundwater table indicates that the upper fractured zone at all four sites is hydraulically active.Key words: fractures, Champlain Sea clay, in situ testing, hydrogeology, geochemistry, hydraulic conductivity.

ISSN:0008-3674    

DOI:10.1139/t94-104

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Contaminant-migration characteristics of fractured Champlain Sea clay were evaluated through laboratory studies and parametric simulations. Two different laboratory diffusion experiments were performed on five unfractured Champlain Sea clay samples. One test involved the placement of a single salt solution (NaCl) in contact with a fully saturated undisturbed clay sample, thus allowing downward chemical migration throughout the sample by diffusion only. The second test involved the placement of deionized water in contact with the undisturbed saturated clay, thus allowing an upward chemical migration by diffusion only. At the termination of the test, the soil samples were sectioned to determine the pore-water and adsorbed concentrations as a function of depth. Diffusion coefficients and retardation factors were determined from plotted data.Simulated profiles were fitted to the field data by using one-dimensional analytical models that represented solute transport in both fractured and unfractured porous media. The fractured simulations using laboratory measured effective diffusion coefficients and retardation factors with advective parameters measured during field investigations provided the best fit. The effectiveness of fractured Champlain Sea clay to retard contaminants migration is significantly reduced when dealing with low- and non-reactive contaminants. Parametric analyses of four hypothetical cases indicate that landfill sites on these clays should be designed with an engineered liner and a leachate collection system.Key words: adsorption, diffusion, laboratory study, contaminant transport, fractured clay.

ISSN:0008-3674    

DOI:10.1139/t94-105

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This overview introduces a series of six papers describing the approach taken in a recent dam safety study to evaluate the liquefaction potential and deformation behaviour for the current seismic setting of Duncan Dam. The dam was originally designed and built in the mid-1960s and is an embankment structure founded on a thick sequence of glacial sediments. The papers were initially presented by a team of B.C. Hydro and their consultants at a specialty session held at the 46th Annual Canadian Conference in Saskatoon in September 1993. The papers provide an excellent summary of the current state of practice in evaluating liquefaction and post-liquefaction behaviour.Key words: embankment, liquefaction, seismic, specialty session.

ISSN:0008-3674    

DOI:10.1139/t94-106

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Duncan Dam is a B.C. Hydro facility constructed on the Duncan River in southeastern British Columbia, Canada, between 1965 and 1967. The dam was founded on a complex sequence of more than 380 m of glacial drift and glaciofluvial sediments, some of which are pervious and compressible. Some sandy units are potentially liquefiable, in particular a sand layer (unit 3c) up to 23 m thick. Current B.C. Hydro seismic guidelines for dams require that Duncan Dam should be able to withstand the Maximum Credible Earthquake (MCE) without catastrophic release of the reservoir. This paper describes the geologic and seismic setting of the region around the dam and the selection of seismic ground motion parameters. Probabilistic methods were applied to develop MCE ground motions, which were estimated to consist of a firm ground peak horizontal acceleration of 0.12 g, which could be caused by aM 6.5 earthquake at a distance of about 50 km. Several time histories with characteristics similar to this design earthquake were selected for dynamic soil analyses.Key words: dam safety, embankment dam, liquefaction, sand, seismicity, seismic ground motion.

ISSN:0008-3674    

DOI:10.1139/t94-107

出版商:NRC Research Press    

年代:1994

数据来源: NRC