摘要:

An empirical model for predicting deposition of coarse-textured debris flows in confined mountain channels is developed based on field measurements of 14 debris flows in the Pacific Northwest, U.S.A. The model uses two criteria for deposition: channel slope (less than 3.5°) and tributary junction angle (greater than 70°). The model is tested by predicting travel distances of 15 debris flows in the Oregon Coast Range and six debris flows in the Washington Cascades, U.S.A. The model is further tested on 44 debris flows in two lithological types in the Oregon Coast Range using aerial photos and topographic maps; on these flows only the approximate travel distance is known. The model can be used by resource professionals to identify the potential for impacts from debris flows.Key words: debris flow, deposition, travel, erosion.

ISSN:0008-3674    

DOI:10.1139/t90-057

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Piezocone data from 83 clay sites are reviewed to investigate first-order trends between measured penetration pore-water stresses (utandubt) and corrected cone-tip resistance (qT). It is shown that the presence of fissures in clay deposits and of fissured crusts significantly affects the pore water stress response. Commercially available piezocones primarily favor the location of the porous element either (1) on the cone tip or face (ut) or (2) just behind the tip (ubt). The former (ut) provides optimal profiling while the latter (ubt) is required for correcting measured cone-tip resistances for pore-water stress effects acting on unequal areas of the cone. The available data indicate thatqTpredominantly reflects penetration pore-water stresses (ut) with measured ratios ofut/qTon the cone face averaging in the order of 0.73 for most intact clays, 0.64 specifically for Leda clays, and 0.46 for fissured clays. Behind the cone tip, the ratio ofubt/qTaverages about 0.53 for intact clays, 0.58 specifically for Leda clays, and near zero or slightly negative for heavily overconsolidated fissured clays.Key words: clays, cone penetrometers, field tests, fissuring,in situtests, penetration tests, piezocones, pore-water stresses.

ISSN:0008-3674    

DOI:10.1139/t90-058

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

During installation of open-pipe piles, soil enters the pile until the inner-soil cylinder develops sufficient resistance to prevent further soil intrusion and the pile becomes "plugged." In spite of its frequent occurrence, only limited attention has thus far been given to this phenomenon and its consequences. The effects of plugging on pile performance and design are examined in reference to the following aspects: ultimate static capacity, time-dependent pile capacity, and dynamic behavior. Pile plugging is shown to have the following effects: marked contribution to the capacity of piles driven in sand; delay in capacity gain with time for piles driven in clay; and change in behavior of piles during installation, causing it to differ from that described by the models commonly used to predict and analyze pile driving.Key words: pipe piles, pile plugging, open-ended piles, static capacity, time-dependent capacity, dynamic analysis, pile driving, pile performance.

ISSN:0008-3674    

DOI:10.1139/t90-059

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A method of simulating downhole and crosshole seismic shear-wave tests in a model under controlled stress conditionsis described. The downhole and shear wave in horizontal plane (SH) crosshole shear waves are generated and received along the principal stress axes using piezoceramic bender elements. TheK0in situstress conditions, including loading and unloading stress paths, are simulated by the hydraulic gradient similitude method, which allows high stresses simulating field conditions to be obtained. The horizontal stress during the tests is directly measured by a lateral total-stress transducer. The test data are used to evaluate various published empirical equations that relate shear-wave velocity and soil stress state. It is found that although the various empirical equations can predict thein situshear-wave velocity profile reasonably well, only the equation that relates the shear-wave velocity to the individual principal stresses in the directions of wave propagation and particle motion can predict the variation of the velocity ratio between the downhole and SH crosshole tests. It was also found that the stress ratio has some effects on the downhole (or shear wave in vertical plane (SV) crosshole) shear-wave velocity, but not on the SH crosshole shear-wave velocity. This indicates that it is only the stress ratio in the plane of wave propagation that is important to the shear-wave velocity. Comparison between the downhole and SH crosshole shows that structure anisotropy is in the order of 10%. In addjtion,K0values are predicted from shear-wave measurement and compared with measured ones. The difficulties in obtainingK0values from shear-wave measurement are also discussed.Key words: hydraulic gradient, model tests, downhole and crosshole shear-wave tests, sand.

ISSN:0008-3674    

DOI:10.1139/t90-060

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

New methods for simultaneous measurement of three orthogonal strains in time-dependent deformation under several stress systems are described. Results of an extensive series of tests on oriented specimens of Queenston shale, with known magnitude and direction ofin situstress, are reported, together with tests on other shales from southern Ontario. It is found that over the stress range expected in field problems, the swelling behaviour is orthotropic and highly stress dependent. The application of stress in one principal direction not only suppresses the swelling in that direction but also reduces the swelling in the orthogonal directions. A method for representing this strongly nonlinear behaviour is described.Key words: shales, Queenston shale, time-dependent deformation, stress dependency, three-dimensional swelling.

ISSN:0008-3674    

DOI:10.1139/t90-061

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Constant strain-rate (0.01/s) uniaxial compression-strength tests were conducted on more than 200 saturated samples of six fine-grained frozen soils at temperatures between −5 and −17 °C. Saturated soil samples containing total water contents between 15% and 105% were prepared using a consolidation apparatus specially designed for this purpose. The effect of dry unit weight, total water content, temperature, and soil type on the behavior of peak compressive strength was studied. Test results indicate the peak compressive strength of fine-grained soils is sensitive to changes in the dry unit weight and the total water content. The temperature dependence of the peak compressive strength is represented by a simple power law. An empirical formula has been developed to predict the peak compressive strength of fine-grained frozen soils at a particular temperature using index properties, specific surface area, particle-size distribution, and dry unit weight. A linear relationship exists between the peak compressive stress and the yield stress.Key words: peak compressive strength, yield stress, frozen soils, fine-grained soils, dry unit weight, failure strain, temperature, total water content, slurry consolidation.

ISSN:0008-3674    

DOI:10.1139/t90-062

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

This paper examines the potential impact on groundwater quality of contaminant migration from a landfill site, through a fractured till, and into an underlying aquifer. The paper describes a simple, semi-analytic technique for modelling contaminant transport through the fractured till, including consideration of diffusion of contaminants from the fractures into the till matrix, sorption, and radioactive decay. The model also considers the finite mass of contaminant and dilution due to the flow of groundwater in the aquifer. The model can be readily implemented on a microcomputer. The model allows examination of variations in fracture spacing, fracture opening size, thickness of the fractured zone, diffusion coefficient, dispersivity, effective porosity of the matrix, radioactive decay, Darcy velocity, thickness of the aquifer, distribution coefficient, and mass of contaminant. The paper describes the results of a limited parametric study that,inter alia, examines the effects of uncertainty in fracture spacing, the thickness of the fractured till, and the effective porosity of the till matrix. Some of the practical implications are discussed.Key words: contaminant migration, fractures, till, groundwater, pollution, landfill, waste disposal.

ISSN:0008-3674    

DOI:10.1139/t90-063

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Unsatisfactory performance of earth and rock-fill dams involving excessive seepage, piping or failure has been attributed to hydrofracture of the core. Although the phenomenon has been reported for some time, important factors influencing hydraulic fracturing pressure, such as saturation and consolidation, have received relatively little attention; nor have results of laboratory tests or theoretical study been directly related to field performance. In this paper, laboratory hydrofracturing tests under well-defined conditions were performed. A simple theoretical expression for fracture pressure is developed involving only conventional soil strength parameters. Case histories involving hydraulic fracturing of the earthcore are reviewed, and "field" hydraulic fracture pressure and crack closure pressure are defined. The results of the laboratory tests show that hydraulic fracture pressure is not a unique soil property; its value depends on the degree of saturation and consolidation. A comparison of the data deduced from case records with test results and theoretical predictions indicates general consistency. The field hydraulic fracturing pressures are bounded in the upper limit by results from saturated-consolidated tests and in the lower limit by results of saturated–unconsolidated hydraulic fracturing tests. It is suggested that the methodology presented may be useful in the assessment of risk of hydraulic fracturing of dams.Key words: earth and rock-fill dams, hydraulic fracture, tensile strength, seepage, Teton Dam.

ISSN:0008-3674    

DOI:10.1139/t90-064

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The impact of leachate on the hydraulic conductivity,k, of a glacial till used in the contraction of a liner for a landfill near Saskatoon, Saskatchewan, is evaluated. Low-gradient triaxial permeability testing of the water-moulded till over a 7-month period with six pore volumes of test leachate at a hydraulic gradient of approximately 100 gave a hydraulic conductivity of 3.0 × 10−9 cm/s, compared with 6.0 × 10−9 cm/s for the water-permeated sample at the same gradient. Thekwas also evaluated at gradients of 20 and 50 during water permeation and found to be 8.0 × 10−9and 6.8 × 10−9 cm/s, respectively. The slight decrease inkwith increase in gradient was attributed to a decrease in void ratio, resulting from a net increase in applied effective stress at the outflow end of the specimen. An assessment of the clay mineral composition of the till at the end of permeability testing did not show collapse of the smectite peak. Instead, the leachate appeared to have actually enhanced the smectite peak relative to the illite peak. It was concluded that the leachate did not have any detrimental impact on the till and that the hydraulic conductivity "of the 0.3-m-thick liner underlying the landfill may not be expected to increase as a result of interaction with leachate.Key words: leachate, soil liners, hydraulic conductivity, smectitic till, X-ray diffraction, triaxial permeability testing.

ISSN:0008-3674    

DOI:10.1139/t90-065

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The shear deformation behaviour along soil–geotextile interfaces has been investigated and is compared with that of the respective soils. Six soils (two sands, two clays, and two peats) in combination with eight different geotextiles (woven and nonwoven) were tested at various conditions in direct shear. It was found that the stiffnesses during shearing for the sand-geotextile interfaces were less than those for the actual sand, by a factor that was largely independent of the normal stress level. The same behaviour was found for the clays and for one of the peats in contact with non-woven geotextiles. For woven geotextile interfaces in contact with the clays and the peats, the load deformation behaviour was generally stiffer than for the actual soils.Key words: geotextiles, differential shear, soil–geotextile interfaces, load transfer during shear.

ISSN:0008-3674    

DOI:10.1139/t90-066

出版商:NRC Research Press    

年代:1990

数据来源: NRC