摘要:

A numerical solution of a spherical and cylindrical cavity expansion problem in sand is presented herein. The underlying theory is unbiased in that it is based directly on experimentally determined stress-strain curves. The solution makes it possible to follow the continuous variation of strains, stresses, and volume changes produced by cavity expansion. It essentially uses the "strain path" approach to determine the state of stress around the cavity, taking into account large strains and the effect of spherical stress variation on the mobilized shear resistance and the associated volume strains. A limited comparison with experimental data shows a reasonable agreement between theory and measurements.Key words: cavities, expansion, sand, stress-strain curves, numerical solution.

ISSN:0008-3674    

DOI:10.1139/t98-028

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Attempts have been made to simulate hillslope creep observations at a site near the village of Tuktoyaktuk, Northwest Territories. Unlike other creep studies in permafrost, this site was unique in that the deformations occurred within a massive ice body, forming the core of a 30 m high concentric hill approximately 1200 m long and 700 m wide. The described simulation model of slope creep is based on both an extension of a closed-form solution originally proposed for two- and three-dimensional ice caps and a finite element creep analysis. The solution covers cyclic temperature fluctuations and incorporates spatial variations of the temperature-dependent creep parameters. Results of simulations are compared with in situ measurements of creep displacements in the hill.Key words: permafrost, slope, creep, in situ measurements, numerical simulation.

ISSN:0008-3674    

DOI:10.1139/t98-024

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

In situ shear tests were performed on soil blocks that contained roots to study the contribution of roots to the shear strength in a case where the shear deformation is not constrained to a thin zone. The shearing resistance of the soil-root system, the tensile force in selected roots, and the deformation of the soil block were measured. The roots were exposed after the test and their positions were determined and used to estimate the initial positions. The root force and the shearing resistance of the soil-root system were estimated with known solutions and compared with measured root force and shearing resistance. None of the roots that passed through the shear zone failed in tension at the maximum displacement. As a consequence, the root resistance is much less than that found in a case where the failure surface is restricted to the boundary between a weak soil and a firm base and where roots are anchored in the firm base and fail in tension. Simplified procedures for estimating root forces are suggested for the case of a thick shear zone.Key words: in situ test, roots, shear strength, slope stability, soil reinforcement, soil–root interaction

ISSN:0008-3674    

DOI:10.1139/t98-027

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The generalized method of slices, commonly used in slope stability analysis, can be extended to determine active earth pressures applied to various types of supports. The governing force and moment equlibrium equations are given. In a similar manner to slope stability analysis, the methods of optimization are used to define the critical slip surface that is associated with the maximum wall pressure. Examples show that the approaches give active earth pressures identical to the Rankine solution for gravity walls. For other types of support, such as anchored or strutted walls, the earth pressure is determined by assigning appropriate locations of the point of application on the wall. It has been found that applying the restrictions of physical admissibility is more vital in earth pressure problems than in slope stability assessments.Key words: earth pressure, limit equilibrium method, the method of slices, retaining walls.

ISSN:0008-3674    

DOI:10.1139/t98-022

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Geotechnical, physical, chemical, and mineralogical properties of the sediments of Ramón López Velarde Park were examined. The site is located in the ancient lacustrine zone of Mexico City. In situ tests included a resistivity survey, soundings with an electric cone, and cross-hole seismic tests. In addition, a continuous core was obtained for the upper 40 m. This core was extensively studied in the laboratory to determine the variation of mineralogy, pH, organic matter, cation exchange capacity (CEC), and structural features with depth. The information is unique with respect to previous studies which focused on specimens at a single depth. Results facilitate the interpretation of the deposit evolution, leading to the current properties of this unique lacustrine sequence.Key words: Mexico City, geotechnical properties, lacustrine sediments, physical properties, mineralogy, chemical propertie

ISSN:0008-3674    

DOI:10.1139/t98-026

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Extensive centrifuge model tests were carried out to investigate optimum compaction density zones within loess embankments 30 and 63.8 m high. In these tests, water infiltration into the slopes and upstream storm water ponds were modelled to simulate the most unfavourable working conditions. Displacement contours in the cross sections were measured and crest settlements were monitored during the tests. Finally, the optimum compaction zoning was analysed based on the comprehensive evaluation of the total crest settlement, the postconstruction settlement, and the slope stability of the embankments. It was indicated that a properly designed high loess embankment could perform satisfactorily with the lower part compacted looser than the conventional code requirements. In terms of total crest settlement and embankment cracking, the degree of compactionKof loess fills should not be less than 0.85 for 30 m high embankments and not less than 0.90 for 63.8 m high embankments. In terms of the postconstruction settlement (<0.2-0.3 m) and construction feasibility, it is expedient to compact the lower one third toK= 0.85, and the top two thirds toK= 0.90 for 63.8 m high embankments. For 30 m high embankments, the bottom zone withK= 0.85 can make up two thirds of the height.Key words: Key words: embankment, centrifuge test, compaction, settlement, stability, loess.

ISSN:0008-3674    

DOI:10.1139/t98-035

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The adsorption and desorption of contaminants on soil and sediment are key mechanisms governing the fate and transport of aqueous-phase hydrocarbons in groundwater. A diffusion batch method for measuring the adsorption coefficient was developed in this study. This method provides a simple and reliable procedure for assessing the adsorption of organic compounds by soil. The method relies on diffusion, rather than shaking and agitation, to bring the solid and solution into chemical equilibrium. Samples of Regina clay, prepared by a variety of methods, were tested for benzene adsorption using this test. Initial testing indicated that equilibrium was attained within 10 days from the start of the adsorption test. The measured adsorption coefficient (Kd) for samples of benzene on Regina clay prepared at various initial water contents (air-dried, liquid limit, slurried, or statically compacted) were in the range of 3.2-7.2 mL/g. A comparison of the diffusion batch method and the conventional ASTM batch method showed that the diffusion batch method has lower variability, particularly over low concentration ranges.Key words: adsorption, diffusion, batch test, adsorption coefficient, organic, benzene, clay.

ISSN:0008-3674    

DOI:10.1139/t98-023

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Geotechnical practitioners and educators may correctly regard the major contributions of centrifuge modelling as relatively substantive and expensive research enterprises. There are, however, many everyday applications of centrifugation that could be made available to both practitioners and educators at a modest cost. Centrifuge modelling and testing at relatively low gravitational levels are particularly relevant to geoenvironmental practice and education; the following applications are typical: (1) centrifuge modelling to produce realistic data on the movement and fate of contaminants in ground water for the validation or further development of numerical simulations; (2) centrifuge testing for the determination of geoenvironmental properties such as hydraulic conductivities and diffusion coefficients in fine-grained soils; (3) centrifuge model design using dimensional similitude for continued education and a better understanding of geoenvironmental concepts. Large commercial modelling centrifuges are beyond the budget of most soils laboratories but smaller dedicated centrifuges, with limited modelling capabilities, can be economically constructed for educational purposes and to produce independent design information that is cost competitive with bench testing.Key words: centrifugal modelling, geoenvironmental practice, education, laboratory centrifuges.

ISSN:0008-3674    

DOI:10.1139/t98-029

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Tapered piles, which have greater top cross sections than bottom ones, have the potential for substantial cost advantages for static loading conditions. However, tapered piles have not often been considered a design option because of the lack of design tools and knowledge about the behaviour of these piles. The objectives of this study are to explore and better understand the operating characteristics of the axial response of tapered piles. A large laboratory facility for testing model piles was developed. In this facility, the soil was contained in a steel soil chamber and pressurized using an air bladder to model the confining pressure. Three instrumented steel piles with different degrees of taper were used in this study. As expected, it was found that as the taper angle increased, the shaft resistance increased. It was found that the shaft resistance of the tapered pile was up to 40% larger than that of the cylindrical pile. The difference in the shaft resistance of the two types decreased for higher values of confining pressure. It was also found that the load distribution along the pile shaft for both pile types had the same pattern. However, this pattern varied as the confining pressure increased. Furthermore, the unit load transfer was significantly affected by the initial sand density for both pile types at low confining pressure, but as the confining pressure increased, this effect diminished. It is concluded that the tapered piles offer a larger resistance than the cylindrical piles. However, for longer piles, it is suggested that the taper be limited to the top length corresponding to 20 diameters.Key words: tapered piles, shaft friction, axial response, load transfer, model testing.

ISSN:0008-3674    

DOI:10.1139/t98-033

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The experiments for modeling soil freeze-thaw and ice action on canal banks were conducted in a laboratory. In addition to the frost heave that was observed during the period of soil freezing, there was an abrupt increase in frost heave that occurred at the beginning of soil thawing. This phenomenon lasted for over approximately 100 hours, and the frost heave induced during this period reached as much as 22.62 mm. At the same time, peak ice pressures also occurred as the soil was thawing. It has been suggested that the frost heave during initial soil thawing may be associated with the change in energy status at the water-ice interface resulting from the buildup of internal stress in the soil during the formation of ice lenses.Key words: frozen soil, freeze-thaw cycle, frost heave, thawing settlement, canal protection.

ISSN:0008-3674    

DOI:10.1139/t98-032

出版商:NRC Research Press    

年代:1998

数据来源: NRC