摘要:

An investigation of the elastic and viscoelastic properties of Nova Scotia coal was carried out over a wide range of strain rates (quasi-static to impact). High resolution stress–strain diagrams for the coal were obtained from compression tests for the lower and medium strain rates up toand with the split Hopkinson bar technique for the high strain rate region up to.The elastic properties of the coal showed a moderate rate sensitivity at low and moderate strain rates.Above the strain rateboth Young's modulus and the stress level of microcracking initiation σf0isplayed extreme rate sensitivity and was found to be a linear function of strain rate. The associated coefficient of viscosity perpendicular to the bedding plane was η* = 3.08 × 104 Pa∙s.The viscoelastic model so determined can be used to assess the elastic properties of coal at even higher strain rates, a situation that is similar to an explosive loading.Keywords: coal, strain rates, dynamic, viscoelastic propertie

ISSN:0008-3674    

DOI:10.1139/t84-024

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The LG 4 dam, the second largest structure on the La Grande Complex of the James Bay hydroelectric development, is 125 m high, about 4 km long, and is composed of 19 × 106 m3of fill materials.The design of the dam is characterised by (i) a zoned earth–rockfill section based on a judicious use of the limited quantities of various materials available, (ii) a 70 m high abutment in the river valley with a steep inclination of about 55°, and (iii) a 50 m high section of the dam with its axis curved in the downstream direction.Detailed stress-deformation analyses were carried out in the critical sections of the dam using finite element methods to verify any presence of arching and hydraulic fracturing potentials in the nonplastic till core. An interesting aspect of these analyses was the fact that the material properties were established based on laboratory testing as well as the observed deformation behaviour of the already completed 156 m high LG 2 main dam.The analyses have indicated that the design has adequate reserve of safety against hydraulic fracturing and arching. Nevertheless, the design sections and material placement requirements were optimised, where necessary, to ensure a satisfactory behaviour of the dam. The instrumentation design was also adapted to the findings of this study.Keywords: earth dam, steep abutment, stress-strain, hydraulic fracturing, arching.

ISSN:0008-3674    

DOI:10.1139/t84-025

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Detailed and regular measurements of the components of the radiation and energy balances and of the thermal and water regimes of the soil to a depth of 5 m were conducted from August 1979 to August 1980 in an open pine forest near lac Hélène, Baie James. The results deriving from these measurements indicate that temperature conditions and thus seasonal frost in the ground are explainable in terms of radiative and heat energy exchanges near the surface, of the physical properties of the soil, of snow accumulation, and of water concentrations and movements in the soil.Keywords: surface energy exchanges, ground temperature, seasonal frost penetration.

ISSN:0008-3674    

DOI:10.1139/t84-026

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Five horizontal drains were installed in a natural clay slope and the piezometric heads in the slope were monitored with piezometers. Decreases of piezometric head in the vicinity of the drains were measured and indicated that horizontal drains can be used to improve the stability of clay slopes.Based on the theory of consolidation, estimates were made of the changes of piezometric head within the test slope due to the installation of drains. Good comparisons were obtained between the predicted and the measured values, demonstrating that the method of prediction can be used with confidence for design purposes. The three-dimensional pattern of piezometric levels was averaged to give an equivalent two-dimensional pattern, and this was used in slope stability calculations to determine the improvement in safety factor of the slope.The effectiveness of horizontal drains depends on the spacing and diameter of the drains, and on their location relative to the critical slip zone.The study has shown that installation of horizontal drains is a viable method of improving the stability of certain clay slopes.Keywords: slope, clay, stability, drains, field test, theory.

ISSN:0008-3674    

DOI:10.1139/t84-027

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Measurements of snow creep pressures from the centre section of a 3.4 m high and 15 m long avalanche-defence supporting structure located on a mountain in western Norway are presented. The site has a deep snow cover and an average slope angle of 25°. The measurement configuration corresponds to plane-strain conditions and the data, along with measured snowpack parameters, allow comparison with simple theoretical predictions. The analysis shows that the average pressure on the structure may be calculated fairly accurately using linear, viscous modelling for the snow deformation. The maximum pressures proved to be higher than that provided by a linear model and this is considered characteristic of nonlinear material. The implications of these results for estimates of design loads are discussed.Keywords: snow pressure, creep, measurements, viscous, plane-strain, finite element.

ISSN:0008-3674    

DOI:10.1139/t84-028

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Research has been conducted over the last several years on the use of geotextiles for mainline heavy tonnage railroad tracks. A wide range of geotextiles was observed to provide improvements in many short-term applications. However, many of these improvements were not long lasting. For longevity of the application a much greater discrimination between geotextile types, geotextile weight, polymer types, and fiber denier was found to be desirable. Also found important was the necessity to match the geotextile properties with the soils engineering properties and to follow correct construction procedures.Drainage was found to be the most critical aspect for achieving long-term stability in the track structure. Excess moisture within the roadbed was found to reduce the subgrade strength and provide easy access for fine grain soils to foul the open ballast. Proper drainage techniques combined with geotextiles are given special consideration.Conclusions are drawn regarding the desirable attributes that should be specified in preparing quality requirements for geotextiles to be obtained under conditions of competitive tendering.Keywords: geotextiles, synthetic fabric, fabric, railroad, tracks, track support, rehabilitation, soil mechanics.

ISSN:0008-3674    

DOI:10.1139/t84-029

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The pore pressure response of a semi-infinite, fully saturated soil mass of finite thickness eroded at a constant rate is examined. Using Terzaghi's classical consolidation theory, an expression is derived for the deficient pore pressure as a function of depth and time. The resulting equation is mildly nonlinear with a moving top boundary. Closed form analytical solutions are obtained for various bottom boundary conditions and are presented in nondimensional quantities. The results indicate that the development of deficient pore pressures is dependent on (i) the rate of soil removal; (ii) the swelling potential of the soil mass; (iii) the ratio of the thickness of soil layer(s) removed to its original thickness; and (iv) the nature of the bottom boundary. Substantial negative pore pressures are likely to persist in the residual mass, even close to the eroded surface, although free water is made available at the top. The plots presented in this paper will be helpful for ascertaining the erosion–swelling characteristics of a soil mass that has been or is being eroded. Examples are presented to illustrate the development and dissipation of deficient pore pressures due to swelling.Keywords: constant rate, deficient pore pressures, depth factor, dredging, erosion–swelling ratio, isochrones, Laplace transform, moving boundary, swelling.

ISSN:0008-3674    

DOI:10.1139/t84-030

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The design, instrumentation, and field performance of two instrumented sections of a geotextile-reinforced embankment are described. The 1–1.5 m high embankment was constructed in three stages on top of a peat deposit that extended to depths of up to 7.6 m. The peat was highly compressible with average water contents of 445% and 785% at the two instrumented sections.A polypropylene, monofilament woven fabric (Permealiner 1195) was used to reinforce the embankment over the less compressible section of the deposit. At stage I, 1.37 m of fill resulted in settlements of approximately 1 m but only 1% transverse strain in the geotextile. At stage II, a total of 3.87 m of fill had been added with total settlements of approximately 3 m and transverse geotextile strain of 21%. Stage III construction involved bringing the embankment to final grade, with a total fill and pavement thickness of 4.2 m. Settlements at stage III were relatively small.A strong, twisted, slit film, polypropylene woven fabric (Geolon 1250) was used to reinforce the more compressible section of the deposit. At stage I, 2.74 m of fill resulted in settlements of approximately 3.1 m and transverse geotextile strains of 3%. At stage II, a total of 6.1 m of fill had been added resulting in settlements of approximately 4.6 m. At stage III, the embankment was brought to grade by reducing the fill thickness and constructing the pavement. The final fill and pavement thickness was 5.7 m.It is concluded that the use of a single layer of even a very strong geotextile was insufficient to prevent large shear deformations in these deep, compressible, peat deposits. The procedures used in the design represented the state-of-the-art at that time; however, they did not provide a good indication of how the embankment would perform in the field. It is recommended that simplified limit equilibrium design procedures should be viewed with considerable caution when designing geotextile-reinforced embankments on peat.Keywords: embankment, muskeg, peat, geotextile, settlement, pore pressures, field observation, instrumentation, soil reinforcement.

ISSN:0008-3674    

DOI:10.1139/t84-031

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

The Jebba Hydroelectric Development, Nigeria, presently under construction, features a 42 m high zoned rockfill embankment founded on river alluvium up to 70 m in depth. The riverbed alluvium comprises fine- to medium- to coarse-grained, quartzitic sands with traces of gravel. The relative densities of the sands vary appreciably in both the vertical and horizontal directions. During the dam design it was found that it would be necessary to densify the loose to medium dense portion of the river sands to maintain settlements within acceptable limits and to withstand design earthquake forces. The top 25 m of the river alluvium is densified by the vibrocompaction method, and below this level down to depths of 40 m the alluvium is densified by blasting. There is no precedent found in the literature for densification by blasting at such depth. This paper presents details of a test program and the production work. Test results conclusively show increases in static cone penetration resistance in loose sand layers several months after blasting.Keywords: cohesionless soils, compaction, dam foundation, deep blasting, densification (soil), penetration tests, sands.

ISSN:0008-3674    

DOI:10.1139/t84-032

出版商:NRC Research Press    

年代:1984

数据来源: NRC

摘要:

Intact block samples of fibrous peat have been obtained using special equipment from two different sites in the James Bay territory in Quebec. Instrumented test fills were subsequently built at those two sites and the observed behaviour was used to check the laboratory data. The laboratory testing program has included standard 24 h incremental tests and stage creep tests where constant loads were applied for periods of about 30 d. Pore pressure and direct permeability measurements were conducted in most of the tests.The tests have been interpreted using the classicale − logpcurves or the tangent modulus approach. The evaluation of compression with time under a constant load has allowed the distinction between primary and secondary consolidation. A certain lag in pore pressure response has been observed and related to incomplete saturation. The coefficient of permeability decreases rapidly with compression as indicated by direct measurements and pore pressure dissipation.The comparison with field observation shows that the 24 h incremental oedometric compression test permits a reasonable prediction of the average settlements at the end of primary consolidation provided the lateral displacement during construction is small. It also shows that the secondary compression observed in the field is about twice what was observed in the laboratory but both show a linear relation with the logarithm of time.Keywords: peat, sampling, compressibility, consolidation, secondary consolidation, permeability, laboratory tests, field behaviour.

ISSN:0008-3674    

DOI:10.1139/t84-033

出版商:NRC Research Press    

年代:1984

数据来源: NRC