摘要:

To assess benefits to be gained from increasing compaction specifications for subgrades, a laboratory program was performed to determine the effect of closed-system freeze–thaw cycling on resilient and residual strains, resilient moduli, and volume changes of till specimens that had been compacted to various densities and water contents and subjected to repetitive loading in a constant triaxial stress system.The study showed that if compaction of this soil was increased to a higher density at a lower water content, strains, modulus, and freeze–thaw effects would be improved to such an extent that a significant reduction in pavement structure would be possible. It also showed that the extent to which a reduction could be made was dependent on the ability of the subgrade to maintain the compaction density and water content throughout its design life.

ISSN:0008-3674    

DOI:10.1139/t71-038

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Using the stress dilatancy relationR = DK, the drained strength of granular material is separated into its dilatant and frictional components. The factors influencing the value of 1 ≤ D ≤ 2 and Kμ ≤ K ≤ Kevare assessed theoretically, and experimental confirmation is provided from tests mainly on River Welland sand. These tests include five different sample geometries, and cell pressures up to 1000 p.s.i. (70.3 kg/cm2). The failure criterion is seen to be contained between two limiting types of behavior relevant to dense and loose assemblies. The main ambiguity exists in the case of axisymmetric extension when the strength is seen to be influenced by the sample boundary conditions.

ISSN:0008-3674    

DOI:10.1139/t71-039

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Twenty-five rockslides in sedimentary strata of the Skeena Mountains in north-central British Columbia are concentrated along a distinct belt approximately 30 km wide. Four slides belong to a "shallow" type, 21 to a "deep" slide type. Regional structural trend, deformation, and lithological heterogeneity seem to control distribution and direction of slip of these rockslides. Slopes oriented parallel to the structural trend and made up of heterogeneous conglomerate, sandstone, shale successions are more likely to fail than others.

ISSN:0008-3674    

DOI:10.1139/t71-040

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Samples of kaolinite, illite, and montmorillonite were consolidated from slurries containing chemical dispersant and flocculating agents. The resulting microstructures of the six clays so produced have been studied in the scanning electron microscope, following a preliminary investigation of the problems of sample disturbance during preparation for electron microscopy. It was seen that dispersed and salt-flocculated structures were formed in the illite clays as a result of their high colloidal activity, but that the inactive kaolinite was relatively insensitive to structural effects. The structures of these artificial clays are compatible with the limited results published on undisturbed natural clays. The small size of the montmorillonite particles led to difficulties in the preparation and scanning operations and no conclusions can be drawn for this clay.

ISSN:0008-3674    

DOI:10.1139/t71-041

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

During the construction of an important foundation with high-capacity bored piles anchored in a shale of variable quality, a technique new to Canada has been used to control the quality of the rock and to determine the necessary depth of embedment of the piles. This technique consists of carrying outin situshearing tests in boreholes below the presumed base of the piles with mean of a "Ménard pressuremeter". These tests allow a direct measurement of an elastic modulus and of a particular shearing resistance of the rock, as well as a semiempirical estimate of the point bearing capacity of the piles. A description of the project, the geological features of the site, and the testing technique is given in this paper, along with the results obtained in a number of typical borings. These results, as well as the validity of the technique, are confirmed by the results of a loading test on a small-diameter pile anchored in the rock.

ISSN:0008-3674    

DOI:10.1139/t71-042

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

Swelling clay minerals present in stiff to hard glacio-lacustrine soils along part of the Don Valley Parkway, Toronto, are believed to have accelerated soil softening and subsequent failure of several slopes only 4 to 8 years after construction. Fairly low residual friction angles of 16° give some indication of the presence of these swelling minerals, whereas low activity values of 0.4 to 0.5 give no indication of their presence.Mineralogic analyses show the soils to consist of abundant illite, chlorite, and carbonate, and moderate amounts of quartz, feldspar, and swelling clay. The swelling clays (10–15% of soils) are an unusual pseudo-montmorillonite formed from soil-vermiculite by adsorption of complex aluminum and iron hydroxide cations in an ancient, acid, weathering environment. Since the clay beds studied have not themselves been weathered, then they must be erosion products from earlier geologic formations in the Toronto area which have not yet been identified.

ISSN:0008-3674    

DOI:10.1139/t71-043

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

A bubbler–manometer water level sensing and recording system for observation wells and stream stage hydrometric stations has produced continuous hydrographs (continuity >90%) throughout winter and summer seasons on an observation well and a hydrometric station. The system utilizes a conventional float-type recorder which operates unattended for a 30-day period. No external energy source is required and the system functions over 100 days on a 224 ft3(6.34 m3) bottle of nitrogen. A protective housing is an integral part of the installation so that the instrument can be safely installed wherever required and will operate throughout the winter without requiring any heating. These features, combined with simplicity of construction and functional durability, makes this design economically attractive for many locations where it is not possible to sense water level changes directly with a float-operated recorder.

ISSN:0008-3674    

DOI:10.1139/t71-044

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

The deposit of marine clays in Lake St. Peter, Quebec, is as much as 300 ft (91 m) deep. Construction of lightpiers was started shortly after the turn of the century but settlement, tilting, and even failures of the structures occurred and construction of the new piers was not continued. As the navigation season is being extended into winter, the need for lightpiers becomes greater. Apart from the sensitive and very compressible clays, the heavy ice forces made a design very difficult. Introducing novel design features and applying the present knowledge of soil mechanics, two piers were designed and built in 1966 on 157 friction piles each, and two more in 1969. An advance field test of pilesin situwas impractical as the structures were in the middle of the lake. Extensive boring and laboratory testing program preceded construction, and the shear strength data of the clay was used for the pile foundation design. Field pile testing confirmed the design assumptions.

ISSN:0008-3674    

DOI:10.1139/t71-045

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

This brief account lists the dimensions, and the soil and climatic conditions concerned in a large landslide which occurred along the South Nation River in Eastern Ontario.

ISSN:0008-3674    

DOI:10.1139/t71-046

出版商:NRC Research Press    

年代:1971

数据来源: NRC

摘要:

The ultimate uplift capacity of augered footings in relatively insensitive and intact clays is computed on the basis of the undrained shear strength of clay. Fissured clays, which may be the result of surface desiccation or preconsolidation, give different values of strength according to the type of test and size of specimen used. The actual strength mobilized in this type of clay under uplift loads was determined by a number of full-scale tests performed on both belled and straight-sided footings. These tests showed that the uplift strength mobilized in fissured clay was only one-third of its intact strength and very nearly equal to its undrained residual or fissured strength. Soil strains adjacent to the belled footings indicated a complex failure mechanism which varied with depth of the foundation. The uplift resistance of straight-sided footings was found to be largely the result of adhesion between the soil and the footing.

ISSN:0008-3674    

DOI:10.1139/t71-047

出版商:NRC Research Press    

年代:1971

数据来源: NRC