摘要:

Soft, fine-grained soils were exposed to cyclic one-dimensional, open-system freezing and thawing, resulting in maximum volume changes of up to 30%, depending on the initial moisture content and plasticity of the clay as well as on the rate of freezing. A linear relationship between the net volume changes subsequent to freezing and thawing and the liquidity index prior to freezing and thawing was obtained. This correlation is not unique, but depends on rate and mode of freezing. Thus, settlements from freeze–thaw consolidation in the field can be predicted from such tests if the rate and mode of freezing are the same as in the field. During cyclic freezing and thawing the soils became fissured and jointed, resulting for most clays in large increases in their bulk permeabilities, which increased with an increasing number of freeze–thaw cycles, often by more than two orders of magnitude. For some materials, however, little change in permeability occured.Key words:cyclic freeze–thaw, clays, freeze–thaw consolidation, permeability, volume chan

ISSN:0008-3674    

DOI:10.1139/t96-079-301

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The Northern till is a thick (~50 m) Late Winsconsinan diamict unit that occurs throughout south-central Ontario. The till has generally been regarded as massive and uniform, with a very low vertical hydraulic conductivity. It is similar to many other till units of mid-continental North American glaciated terrain in that it is believed to inhibit recharge to underlying aquifers and afford a high degree of protection to these aquifers from surface and near-surface sources of contamination. Standard methods of estimating hydraulic conductivity (K) for the Northern till, such as laboratory testing of core samples (other studies) and rising–falling head field piezometer tests (this study and other studies), characteristically yield values on the order of 10–11to 10–9m/s. Typically, these values indicate advective traveltimes through the till on the order of hundreds to thousands of years. In contrast, isotopic evidence (2H,18O, and3H) from till pore waters indicates the presence of modern (post-1952) waters at depths of up to 50 m, suggesting either that certain facies of the till are considerably more permeable or that minor sand lenses or hydrogeologically active secondary permeability structures are locally important. In some areas, vertical flow velocities may approach 1 m/year. By comparing pore-water isotopic data from cores acquired using mud (sodium bentonite) and dry rotary methods, this study further demonstrates that representative pore-water samples can be obtained using a drilling fluid providing care is taken in preparing core samples for analysis.Key words:till, aquitard, permeability, recharge, contaminant transport, isotop

ISSN:0008-3674    

DOI:10.1139/t96-080-302

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

There are two sampling operations for field quality control of an earth dam: the random and the purposive. Both have been well established by their long use in engineering projects, but are fundamentally different in their basic assumptions, approach, and interpretation of results. They are analyzed herein and their basic similarities and differences are compared. The intent is to provide the proper perspective for an objective selection and subsequent implementation of one or the other operation. It is concluded that both operations can be implemented, singly or jointly, on a project, provided that inherent potentialities and limitations are clearly recognized and evaluated throughout design and construction.Key words:earth dam, rockfill, sampling, statistical analysis, quality control, quality assurance.

ISSN:0008-3674    

DOI:10.1139/t96-081-303

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The Brasília underground transportation system comprises 6.5 km of shallow tunnel excavated in a soft red soil known as porous clay that overlies harder residual soils. The tunnel diameter is 9.6 m. Settlement observations indicated that surface settlements were two to three fold the initially predicted value, although no indication of excavation instability was observed. Settlements reached, at one section, 500 mm without failure. Another striking feature was settlement amplification between the top of the excavation and the surface by a factor that averaged 1.2 but reached up to 4. This occured because of the collapsible nature of the porous clay, which presented a considerable reduction of volume as the tunnel face advanced. This paper describes tunnel design, construction, and instrumentation; and summarizes geology and soil properties from in situ and laboratory tests. Field measurements of settlements and horizontal displacements are described and analysed. The main cause of the large settlements was collapse of the porous clay structure.Key words:tunnelling, porous clay, settlements, collapse.

ISSN:0008-3674    

DOI:10.1139/t96-082-304

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

This paper examines the static equilibrium of drag anchors during embedment in sand. A limit equilibrium method is developed to allow the anchor holding capacity to be predicted given a specific anchor geometry and position relative to the free surface of the sand. The method is based on the earlier approach of Le Lievre and Tabatabaee, but is extended to include a three-dimensional soil wedge, which is consistent with experimental observation. The solution procedure is also extended to be more applicable for anchors at a preultimate stage by incorporating a force behind the anchor fluke. To calibrate the method, a series of centrifuge model anchor tests has been performed in silica and calcareous sands. The static capacity of the anchor during embedment is compared with the static limit equilibrium solution and good agreement is demonstrated.Key words:drag anchor, statics, sand, limit equilibrium, ultimate holding capacity.

ISSN:0008-3674    

DOI:10.1139/t96-083-305

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The kinematic behaviour of drag achors during embedment in sand is examined in this paper. A series of centrifuge model anchor tests has been performed in silica and calcareous sands in which both force and kinematic data were obtained during the course of anchor embedment. In this paper, the kinematic data have been examined to determine general rules for the kinematic behaviour of a drag anchor during embedment. These rules provide an essential step towards a theoretical simulation of a complete anchor embedment history and hence a predictive tool for the ultimate holding capacity of a drag anchor.Key words:drag anchor, kinematics, sand, limit equilibrium, ultimate holding capacity.

ISSN:0008-3674    

DOI:10.1139/t96-084-306

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The saturated and unsaturated shear strength behavior of an undisturbed, completely decomposed fine ash tuff and an undisturbed, completely decomposed granite from Hong Kong were studied using direct shear and triaxial tests. The completely decomposed fine ash tuff is a fine- to medium-grained saprolite. The completely decomposed granite is a coarse-grained saprolite. Results show that matric suction increases the shear strength of both soils. The extent of the increase is the shear strength with matric suction is related to the soil-water characteristic curve for the soil and to the amount of dilation during shear. The effect of matric suction on the shear strength was more pronounced for the fine- to medium-grained completely decomposed fine ash tuff than for the coarse-grained completely decomposed granite. These studies on the saprolitic soils provide insight into the understanding of the shear strength of unsaturated, coarse-grained soils.Key words:saprolites, shear strength, matric suction, triaxial, direct shear, coarse-grained soils.

ISSN:0008-3674    

DOI:10.1139/t96-085-307

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Cavern of up to 10 m in diameter were mined in oil sand and shale formations at depths of 500 m in Cold Lake, Alberta. The cavens were subjected to high-pressure water jetting, pumping bitumen–sand slurry to the surface, cyclic water pressurization and depressurization, and gas exsolution. Roof and wall shapes were monitored by sonar logs. Numerical models are proposed to explain the roof and wall sloughing mechanisms in oil sand and shale.Key words:oil sand, shale, cavern, water jetting, collapse mechanism

ISSN:0008-3674    

DOI:10.1139/t96-086-308

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

A slope stability study involving shallow slip surfaces should include the effect of negative pore-water pressures in a slope. A field instrumentation program was carried out to monitor negative pore-water pressure (i.e., in situ matric suction) in a residual soil slope in Singapore. Variations in matric suction and the matric suction profiles under (1) a canvas-convered grassed surface, (2) a grassed surface, and (3) a bare ground surface, in response to rainfalls were investigated. Changes in matric suction due to changes in climatic conditions decrease rapidly with depth. The change was found to be most significant in the bare slope and least significant under the canvas-covered slope. The amount of decrease in matric suction after a rainstorm was observed to be a function of the initial matric suction just prior to the rainstorm. Positive pore-water pressures were observed above the groundwater table, suggesting the development of a perched water table within the slope. These observations are also typical of other regions experiencing high seasonal rainfalls. The field monitoring program presented can be adopted for investigating rainfall-induced landslides in other parts of the world.Key words:matric suction, negative pore-water pressure, field instrumentation, rainfall, residual soil, slope stability.

ISSN:0008-3674    

DOI:10.1139/t96-087

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Frost load is an important loading condition to consider for the design of buried pipes. Though frost loads can be much greater than earth loads, it is not presently possible to estimate frost loads except using heuristic arguments. This paper describes the development of simplified methods to estimate frost load. Important variables are identified that can explain how the effects of frost loading can be mitigated. Sensitivity analyses are presented to highlight the importance of the different variables involved in the simplified methods. Frost loads measured in a field case study are compared with calculated frost loads in trenches with clay and sand backfills.Key words:frost load, frost depth, buried pipe, trench backfills, trench width.

ISSN:0008-3674    

DOI:10.1139/t96-088-309

出版商:NRC Research Press    

年代:1996

数据来源: NRC