摘要:

A mechanism is proposed by which debris flows can be triggered through impulsive loading. Momentum transferred from hillslope failures to steep stream bed materials may be sufficient to initiate a debris flow where one may not otherwise occur. An important parameter in the momentum transfer is the planimetric angle between the slide path axis and the stream channel axis. Preliminary stability equations for both drained and undrained loading are developed from formulae commonly used to assess stream channel stability. Case studies from two basins in the southern Coast Mountains of British Columbia are used to illustrate the mechanisms.Key words: debris flow, triggering, mechanisms, rock slide, debris slide, Coast Mountains.

ISSN:0008-3674    

DOI:10.1139/t92-040

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The Highvale mine, west of Edmonton, Alta., is a strip-mining operation with Upper Cretaceous soft sandstone and mudstone overlying the coal deposit. Highwalls cut in the soft rock experienced numerous failures from 1983 to 1985 that disrupted stripping and mining operations and posed a threat to safety. The performance of a 20–23 m highwall at Highvale was studied in 1987 and 1988 to gain insight to the mechanisms of failure. The study utilized surveying, slope indicators, and piezometers to determine the deformation and seepage pattern behind the highwall as it rebounded into the pit upon excavation. Translational movements were found to extend over 250 m behind the highwall along weak, probably presheared bentonitic mudstones. The sandstone and mudstone overburden was observed to extend toward the open pit. This affected the pore-pressure regime and led to a reduction in the mass strength of the sandstone and mudstone. The findings of this study contributed to a better understanding of the mechanisms of highwall failure in soft sedimentary rocks.Key words: highwall, deformations, failure, seepage, loosening, softening.

ISSN:0008-3674    

DOI:10.1139/t92-041

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

In the absence of impervious natural soils, compacted mixtures of bentonite and sand have been used to form barriers to fluids, and the focus of this paper is on the hydraulic conductivity behaviour of these compacted mixtures. Results of laboratory investigations are presented to show the influences of bentonite–sand content, compaction water content, system chemistry, and changes of system chemistry. Some of the findings are as follows: (i) low hydraulic conductivity requires continuity of the bentonite matrix within the mixture, and this in turn requires both adequate bentonite content and adequate bentonite distribution (i.e., mixing); (ii) in well-compacted mixtures containing up to 20% bentonite in dry mass, sand forms the load-supporting framework and gives the mixtures dimensional stability at the macro level (crack resistance); and (iii) the hydraulic conductivity of mixtures containing freshwater, high-swell bentonite, when permeated with a strong saline solution, increased by only small amounts, suggesting that the fabric of bentonite enclosed within the sand framework was little influenced by this change of system chemistry.Key words: mixture, bentonite, sand, permeability, laboratory study.

ISSN:0008-3674    

DOI:10.1139/t92-042

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The hydraulic structures of the proposed site C hydroelectric project in northeastern British Columbia would require deep excavations in Lower Cretaceous Shaftesbury shales. A significant stress relief would occur over most of the area to be occupied by the structures. Concerns about the magnitude and rate of time-dependent rebound and their impacts on project design, construction, and operation have been addressed. A review was made of several important case histories of other major projects constructed on Prairie shales. The properties of those shales were compared with the Shaftesbury shales. Long-term testing to establish the shale swelling characteristics was performed. Analyses were then made to evaluate potential elastic and time-dependent rebounds of the project area. A procedure for computing stress changes and time-dependent deformations due to the unloading effect of excavation followed by structural loading was developed. The procedure is useful in determining differential rebound that would occur in areas of steep topography or significant variations in the distribution of structural loads.Key words: rebound, shales, dam, swelling properties, swelling pressure, stress relief, deep excavations.

ISSN:0008-3674    

DOI:10.1139/t92-043

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

This paper describes the results of short-term pullout tests and long-term full-scale measurements of negative skin friction on driven piles in Bangkok subsoils. Two instrumented cylindrical (hollow) prestressed concrete piles were fully equipped with two independent load-measurement systems, load cells, and telltale rods. Pore pressures and ground movements in the vicinity of the piles were monitored throughout the period of investigation. The effect of bitumen coating on negative skin friction was also studied. The long-term behaviour of driven piles was compared with the estimated values obtained from short-term pullout tests and soil strength data. It was found that the negative skin friction can be predicted well by the effective stress approach using values of β between 0.1 and 0.2. The load–settlement and load–transfer behaviour were numerically modelled to acquire a more comprehensive understanding of negative skin friction developed on driven piles. A settlement-controlled concept is also introduced for piles subjected to negative skin friction, on the basis of these findings.Key words: consolidation, downdrag, driven pile, embankment, finite elements, pore pressures, pullout, settlements, soft clay.

ISSN:0008-3674    

DOI:10.1139/t92-044

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Laboratory flume deposition tests were carried out to study the physical phenomena associated with the deposition of a sand slurry to form a hydraulic fill. The experimental apparatus was carefully designed to minimize flume-wall effects on the flow and to allow discharge of slurry of constant composition for an indefinite period of time. Slurry concentration and flow rate were varied independently to study their effects on characteristics of the fill such as geometry, grain-size distribution, and density. Three different sands were used to evaluate the influence of the mean grain size.Key words: hydraulic fill, flume tests, sand, profile, slope, density.

ISSN:0008-3674    

DOI:10.1139/t92-045

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Several flume deposition tests carried out in different parts of the world to study hydraulic fills are compared and discussed. The results of all test programs are coherent and consistent with field observations of hydraulic fills and natural alluvial deposits, which suggests that, at least qualitatively, flume tests are adequate to simulate the physical phenomena associated with hydraulic deposition.Key words: hydraulic fill, flume tests, sand, grain size, profile, slope, density.

ISSN:0008-3674    

DOI:10.1139/t92-046

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

A probabilistic method is used in this study to investigate the safety of an anchored sheet-pile wall embedded in a cohesionless soil. Two different definitions of the structure's limit state are given for reference. Failure probability is estimated in terms of overall stability, specifically with reference to the upper soil anchor. The probabilistic analysis is based on a second level approximate computation method (Rosenblueth point estimate method). The friction angle and the soil unit weight are the assumed independent and uncorrelated stochastic variables.Key words: probability, sheet-pile wall, active and passive pressure, friction angle, safety factor, safety margin, reliability index.

ISSN:0008-3674    

DOI:10.1139/t92-047

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The paper discusses approaches for interpreting nonlinear stiffness data from undrained pressuremeter tests. An approximate simplified method is proposed for transforming curves of pressuremeter modulus (against cavity strain) into equivalent single element plots. The new approach is illustrated using field data obtained in two quite different clays, with generally good agreement being found between pressuremeter-derived data and high-quality laboratory experiments. However, the results indicate a tendency for the laboratory stiffness curves to plot above the pressuremeter characteristics in clays with a low overconsolidation ratio and vice versa for heavily overconsolidated deposits. The reasons for these discrepancies are explored, and it is concluded that disturbance during installation and initial cavity expansion is the most important factor for the observed differences.Key words: shear stiffness, nonlinearity, pressuremeter, clay.

ISSN:0008-3674    

DOI:10.1139/t92-048

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Cone penetration testing (CPT) in Canada is usually performed using locally available drilling rigs. The limited pushing capacity of most drilling rigs coupled with the risk of damage to expensive cone penetrometers has tended to restrict the CPT to generally loose or soft soils. Therefore, in regions dominated by stiff glacial soils the more rugged standard penetration test (SPT) is still the most commonly usedin situtest during geotechnical investigations. However, there are many limitations with the SPT with respect to interpretation and repeatability, especially the uncertainty with the energy delivered from various SPT hammer anvil systems. A downhole cone penetration test (DCPT) has been developed by modifying the equipment and procedure of the standard electric CPT. The DCPT consists of a simple, inexpensive electric cone penetrometer attached to a 1.5 m (5 ft) length of AW drill rod. The test is performed by pushing the cone 1.5 m into the base of an open borehole to produce a continuous profile of penetration resistanceQc, over the 1.5-m interval or whatever interval penetration is possible. The test incorporates the simplicity, ruggedness, and depth capability of the SPT but is able to define a near-continuous, accurate, and repeatable cone penetration resistance profile. The equipment and procedure of the DCPT is described in detail, and results from a near-continuous DCPT and an adjacent continuous CPT are presented and compared with the results obtained from an adjacent borehole with SPT. Excellent agreement was found between the results of the DCPT and the CPT.Key words:in situ, cone penetration testing, stiff soils.

ISSN:0008-3674    

DOI:10.1139/t92-049

出版商:NRC Research Press    

年代:1992

数据来源: NRC